mirror of
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e5137b50a0
Since the introduction of PREEMPT_NEED_RESCHED in:
f27dde8dee ("sched: Add NEED_RESCHED to the preempt_count")
we need to be able to look at both TIF_NEED_RESCHED and
PREEMPT_NEED_RESCHED to understand the full preemption behaviour.
Add it to the trace output.
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Fengguang Wu <fengguang.wu@intel.com>
Cc: Huang Ying <ying.huang@intel.com>
Cc: Yuanhan Liu <yuanhan.liu@linux.intel.com>
Link: http://lkml.kernel.org/r/20131004152826.GP3081@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2812 lines
104 KiB
Plaintext
2812 lines
104 KiB
Plaintext
ftrace - Function Tracer
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========================
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Copyright 2008 Red Hat Inc.
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Author: Steven Rostedt <srostedt@redhat.com>
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License: The GNU Free Documentation License, Version 1.2
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(dual licensed under the GPL v2)
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Reviewers: Elias Oltmanns, Randy Dunlap, Andrew Morton,
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John Kacur, and David Teigland.
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Written for: 2.6.28-rc2
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Updated for: 3.10
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Introduction
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------------
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Ftrace is an internal tracer designed to help out developers and
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designers of systems to find what is going on inside the kernel.
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It can be used for debugging or analyzing latencies and
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performance issues that take place outside of user-space.
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Although ftrace is typically considered the function tracer, it
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is really a frame work of several assorted tracing utilities.
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There's latency tracing to examine what occurs between interrupts
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disabled and enabled, as well as for preemption and from a time
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a task is woken to the task is actually scheduled in.
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One of the most common uses of ftrace is the event tracing.
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Through out the kernel is hundreds of static event points that
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can be enabled via the debugfs file system to see what is
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going on in certain parts of the kernel.
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Implementation Details
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----------------------
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See ftrace-design.txt for details for arch porters and such.
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The File System
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---------------
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Ftrace uses the debugfs file system to hold the control files as
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well as the files to display output.
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When debugfs is configured into the kernel (which selecting any ftrace
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option will do) the directory /sys/kernel/debug will be created. To mount
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this directory, you can add to your /etc/fstab file:
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debugfs /sys/kernel/debug debugfs defaults 0 0
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Or you can mount it at run time with:
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mount -t debugfs nodev /sys/kernel/debug
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For quicker access to that directory you may want to make a soft link to
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it:
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ln -s /sys/kernel/debug /debug
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Any selected ftrace option will also create a directory called tracing
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within the debugfs. The rest of the document will assume that you are in
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the ftrace directory (cd /sys/kernel/debug/tracing) and will only concentrate
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on the files within that directory and not distract from the content with
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the extended "/sys/kernel/debug/tracing" path name.
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That's it! (assuming that you have ftrace configured into your kernel)
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After mounting debugfs, you can see a directory called
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"tracing". This directory contains the control and output files
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of ftrace. Here is a list of some of the key files:
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Note: all time values are in microseconds.
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current_tracer:
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This is used to set or display the current tracer
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that is configured.
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available_tracers:
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This holds the different types of tracers that
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have been compiled into the kernel. The
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tracers listed here can be configured by
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echoing their name into current_tracer.
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tracing_on:
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This sets or displays whether writing to the trace
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ring buffer is enabled. Echo 0 into this file to disable
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the tracer or 1 to enable it. Note, this only disables
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writing to the ring buffer, the tracing overhead may
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still be occurring.
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trace:
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This file holds the output of the trace in a human
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readable format (described below).
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trace_pipe:
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The output is the same as the "trace" file but this
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file is meant to be streamed with live tracing.
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Reads from this file will block until new data is
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retrieved. Unlike the "trace" file, this file is a
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consumer. This means reading from this file causes
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sequential reads to display more current data. Once
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data is read from this file, it is consumed, and
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will not be read again with a sequential read. The
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"trace" file is static, and if the tracer is not
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adding more data,they will display the same
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information every time they are read.
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trace_options:
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This file lets the user control the amount of data
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that is displayed in one of the above output
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files. Options also exist to modify how a tracer
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or events work (stack traces, timestamps, etc).
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options:
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This is a directory that has a file for every available
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trace option (also in trace_options). Options may also be set
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or cleared by writing a "1" or "0" respectively into the
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corresponding file with the option name.
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tracing_max_latency:
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Some of the tracers record the max latency.
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For example, the time interrupts are disabled.
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This time is saved in this file. The max trace
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will also be stored, and displayed by "trace".
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A new max trace will only be recorded if the
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latency is greater than the value in this
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file. (in microseconds)
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tracing_thresh:
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Some latency tracers will record a trace whenever the
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latency is greater than the number in this file.
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Only active when the file contains a number greater than 0.
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(in microseconds)
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buffer_size_kb:
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This sets or displays the number of kilobytes each CPU
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buffer holds. By default, the trace buffers are the same size
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for each CPU. The displayed number is the size of the
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CPU buffer and not total size of all buffers. The
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trace buffers are allocated in pages (blocks of memory
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that the kernel uses for allocation, usually 4 KB in size).
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If the last page allocated has room for more bytes
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than requested, the rest of the page will be used,
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making the actual allocation bigger than requested.
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( Note, the size may not be a multiple of the page size
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due to buffer management meta-data. )
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buffer_total_size_kb:
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This displays the total combined size of all the trace buffers.
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free_buffer:
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If a process is performing the tracing, and the ring buffer
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should be shrunk "freed" when the process is finished, even
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if it were to be killed by a signal, this file can be used
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for that purpose. On close of this file, the ring buffer will
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be resized to its minimum size. Having a process that is tracing
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also open this file, when the process exits its file descriptor
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for this file will be closed, and in doing so, the ring buffer
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will be "freed".
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It may also stop tracing if disable_on_free option is set.
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tracing_cpumask:
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This is a mask that lets the user only trace
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on specified CPUs. The format is a hex string
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representing the CPUs.
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set_ftrace_filter:
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When dynamic ftrace is configured in (see the
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section below "dynamic ftrace"), the code is dynamically
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modified (code text rewrite) to disable calling of the
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function profiler (mcount). This lets tracing be configured
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in with practically no overhead in performance. This also
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has a side effect of enabling or disabling specific functions
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to be traced. Echoing names of functions into this file
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will limit the trace to only those functions.
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This interface also allows for commands to be used. See the
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"Filter commands" section for more details.
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set_ftrace_notrace:
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This has an effect opposite to that of
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set_ftrace_filter. Any function that is added here will not
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be traced. If a function exists in both set_ftrace_filter
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and set_ftrace_notrace, the function will _not_ be traced.
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set_ftrace_pid:
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Have the function tracer only trace a single thread.
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set_graph_function:
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Set a "trigger" function where tracing should start
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with the function graph tracer (See the section
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"dynamic ftrace" for more details).
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available_filter_functions:
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This lists the functions that ftrace
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has processed and can trace. These are the function
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names that you can pass to "set_ftrace_filter" or
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"set_ftrace_notrace". (See the section "dynamic ftrace"
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below for more details.)
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enabled_functions:
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This file is more for debugging ftrace, but can also be useful
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in seeing if any function has a callback attached to it.
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Not only does the trace infrastructure use ftrace function
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trace utility, but other subsystems might too. This file
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displays all functions that have a callback attached to them
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as well as the number of callbacks that have been attached.
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Note, a callback may also call multiple functions which will
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not be listed in this count.
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If the callback registered to be traced by a function with
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the "save regs" attribute (thus even more overhead), a 'R'
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will be displayed on the same line as the function that
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is returning registers.
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function_profile_enabled:
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When set it will enable all functions with either the function
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tracer, or if enabled, the function graph tracer. It will
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keep a histogram of the number of functions that were called
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and if run with the function graph tracer, it will also keep
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track of the time spent in those functions. The histogram
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content can be displayed in the files:
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trace_stats/function<cpu> ( function0, function1, etc).
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trace_stats:
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A directory that holds different tracing stats.
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kprobe_events:
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Enable dynamic trace points. See kprobetrace.txt.
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kprobe_profile:
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Dynamic trace points stats. See kprobetrace.txt.
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max_graph_depth:
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Used with the function graph tracer. This is the max depth
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it will trace into a function. Setting this to a value of
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one will show only the first kernel function that is called
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from user space.
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printk_formats:
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This is for tools that read the raw format files. If an event in
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the ring buffer references a string (currently only trace_printk()
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does this), only a pointer to the string is recorded into the buffer
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and not the string itself. This prevents tools from knowing what
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that string was. This file displays the string and address for
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the string allowing tools to map the pointers to what the
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strings were.
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saved_cmdlines:
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Only the pid of the task is recorded in a trace event unless
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the event specifically saves the task comm as well. Ftrace
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makes a cache of pid mappings to comms to try to display
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comms for events. If a pid for a comm is not listed, then
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"<...>" is displayed in the output.
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snapshot:
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This displays the "snapshot" buffer and also lets the user
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take a snapshot of the current running trace.
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See the "Snapshot" section below for more details.
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stack_max_size:
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When the stack tracer is activated, this will display the
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maximum stack size it has encountered.
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See the "Stack Trace" section below.
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stack_trace:
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This displays the stack back trace of the largest stack
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that was encountered when the stack tracer is activated.
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See the "Stack Trace" section below.
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stack_trace_filter:
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This is similar to "set_ftrace_filter" but it limits what
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functions the stack tracer will check.
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trace_clock:
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Whenever an event is recorded into the ring buffer, a
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"timestamp" is added. This stamp comes from a specified
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clock. By default, ftrace uses the "local" clock. This
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clock is very fast and strictly per cpu, but on some
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systems it may not be monotonic with respect to other
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CPUs. In other words, the local clocks may not be in sync
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with local clocks on other CPUs.
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Usual clocks for tracing:
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# cat trace_clock
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[local] global counter x86-tsc
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local: Default clock, but may not be in sync across CPUs
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global: This clock is in sync with all CPUs but may
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be a bit slower than the local clock.
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counter: This is not a clock at all, but literally an atomic
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counter. It counts up one by one, but is in sync
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with all CPUs. This is useful when you need to
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know exactly the order events occurred with respect to
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each other on different CPUs.
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uptime: This uses the jiffies counter and the time stamp
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is relative to the time since boot up.
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perf: This makes ftrace use the same clock that perf uses.
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Eventually perf will be able to read ftrace buffers
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and this will help out in interleaving the data.
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x86-tsc: Architectures may define their own clocks. For
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example, x86 uses its own TSC cycle clock here.
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To set a clock, simply echo the clock name into this file.
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echo global > trace_clock
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trace_marker:
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This is a very useful file for synchronizing user space
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with events happening in the kernel. Writing strings into
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this file will be written into the ftrace buffer.
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It is useful in applications to open this file at the start
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of the application and just reference the file descriptor
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for the file.
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void trace_write(const char *fmt, ...)
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{
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va_list ap;
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char buf[256];
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int n;
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if (trace_fd < 0)
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return;
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va_start(ap, fmt);
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n = vsnprintf(buf, 256, fmt, ap);
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va_end(ap);
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write(trace_fd, buf, n);
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}
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start:
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trace_fd = open("trace_marker", WR_ONLY);
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uprobe_events:
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Add dynamic tracepoints in programs.
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See uprobetracer.txt
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uprobe_profile:
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Uprobe statistics. See uprobetrace.txt
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instances:
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This is a way to make multiple trace buffers where different
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events can be recorded in different buffers.
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See "Instances" section below.
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events:
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This is the trace event directory. It holds event tracepoints
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(also known as static tracepoints) that have been compiled
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into the kernel. It shows what event tracepoints exist
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and how they are grouped by system. There are "enable"
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files at various levels that can enable the tracepoints
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when a "1" is written to them.
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See events.txt for more information.
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per_cpu:
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This is a directory that contains the trace per_cpu information.
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per_cpu/cpu0/buffer_size_kb:
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The ftrace buffer is defined per_cpu. That is, there's a separate
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buffer for each CPU to allow writes to be done atomically,
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and free from cache bouncing. These buffers may have different
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size buffers. This file is similar to the buffer_size_kb
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file, but it only displays or sets the buffer size for the
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specific CPU. (here cpu0).
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per_cpu/cpu0/trace:
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This is similar to the "trace" file, but it will only display
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the data specific for the CPU. If written to, it only clears
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the specific CPU buffer.
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per_cpu/cpu0/trace_pipe
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This is similar to the "trace_pipe" file, and is a consuming
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read, but it will only display (and consume) the data specific
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for the CPU.
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per_cpu/cpu0/trace_pipe_raw
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For tools that can parse the ftrace ring buffer binary format,
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the trace_pipe_raw file can be used to extract the data
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from the ring buffer directly. With the use of the splice()
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system call, the buffer data can be quickly transferred to
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a file or to the network where a server is collecting the
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data.
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Like trace_pipe, this is a consuming reader, where multiple
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reads will always produce different data.
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per_cpu/cpu0/snapshot:
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This is similar to the main "snapshot" file, but will only
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snapshot the current CPU (if supported). It only displays
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the content of the snapshot for a given CPU, and if
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written to, only clears this CPU buffer.
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per_cpu/cpu0/snapshot_raw:
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Similar to the trace_pipe_raw, but will read the binary format
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from the snapshot buffer for the given CPU.
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per_cpu/cpu0/stats:
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This displays certain stats about the ring buffer:
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entries: The number of events that are still in the buffer.
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overrun: The number of lost events due to overwriting when
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the buffer was full.
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commit overrun: Should always be zero.
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This gets set if so many events happened within a nested
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event (ring buffer is re-entrant), that it fills the
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buffer and starts dropping events.
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bytes: Bytes actually read (not overwritten).
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oldest event ts: The oldest timestamp in the buffer
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now ts: The current timestamp
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dropped events: Events lost due to overwrite option being off.
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read events: The number of events read.
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The Tracers
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-----------
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Here is the list of current tracers that may be configured.
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"function"
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Function call tracer to trace all kernel functions.
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"function_graph"
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Similar to the function tracer except that the
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function tracer probes the functions on their entry
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whereas the function graph tracer traces on both entry
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and exit of the functions. It then provides the ability
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to draw a graph of function calls similar to C code
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source.
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"irqsoff"
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Traces the areas that disable interrupts and saves
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the trace with the longest max latency.
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See tracing_max_latency. When a new max is recorded,
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it replaces the old trace. It is best to view this
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trace with the latency-format option enabled.
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"preemptoff"
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Similar to irqsoff but traces and records the amount of
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time for which preemption is disabled.
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"preemptirqsoff"
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Similar to irqsoff and preemptoff, but traces and
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records the largest time for which irqs and/or preemption
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is disabled.
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"wakeup"
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Traces and records the max latency that it takes for
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the highest priority task to get scheduled after
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it has been woken up.
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Traces all tasks as an average developer would expect.
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"wakeup_rt"
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Traces and records the max latency that it takes for just
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RT tasks (as the current "wakeup" does). This is useful
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for those interested in wake up timings of RT tasks.
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"nop"
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This is the "trace nothing" tracer. To remove all
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tracers from tracing simply echo "nop" into
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current_tracer.
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Examples of using the tracer
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----------------------------
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Here are typical examples of using the tracers when controlling
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them only with the debugfs interface (without using any
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user-land utilities).
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Output format:
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--------------
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Here is an example of the output format of the file "trace"
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--------
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# tracer: function
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#
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# entries-in-buffer/entries-written: 140080/250280 #P:4
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#
|
|
# _-----=> irqs-off
|
|
# / _----=> need-resched
|
|
# | / _---=> hardirq/softirq
|
|
# || / _--=> preempt-depth
|
|
# ||| / delay
|
|
# TASK-PID CPU# |||| TIMESTAMP FUNCTION
|
|
# | | | |||| | |
|
|
bash-1977 [000] .... 17284.993652: sys_close <-system_call_fastpath
|
|
bash-1977 [000] .... 17284.993653: __close_fd <-sys_close
|
|
bash-1977 [000] .... 17284.993653: _raw_spin_lock <-__close_fd
|
|
sshd-1974 [003] .... 17284.993653: __srcu_read_unlock <-fsnotify
|
|
bash-1977 [000] .... 17284.993654: add_preempt_count <-_raw_spin_lock
|
|
bash-1977 [000] ...1 17284.993655: _raw_spin_unlock <-__close_fd
|
|
bash-1977 [000] ...1 17284.993656: sub_preempt_count <-_raw_spin_unlock
|
|
bash-1977 [000] .... 17284.993657: filp_close <-__close_fd
|
|
bash-1977 [000] .... 17284.993657: dnotify_flush <-filp_close
|
|
sshd-1974 [003] .... 17284.993658: sys_select <-system_call_fastpath
|
|
--------
|
|
|
|
A header is printed with the tracer name that is represented by
|
|
the trace. In this case the tracer is "function". Then it shows the
|
|
number of events in the buffer as well as the total number of entries
|
|
that were written. The difference is the number of entries that were
|
|
lost due to the buffer filling up (250280 - 140080 = 110200 events
|
|
lost).
|
|
|
|
The header explains the content of the events. Task name "bash", the task
|
|
PID "1977", the CPU that it was running on "000", the latency format
|
|
(explained below), the timestamp in <secs>.<usecs> format, the
|
|
function name that was traced "sys_close" and the parent function that
|
|
called this function "system_call_fastpath". The timestamp is the time
|
|
at which the function was entered.
|
|
|
|
Latency trace format
|
|
--------------------
|
|
|
|
When the latency-format option is enabled or when one of the latency
|
|
tracers is set, the trace file gives somewhat more information to see
|
|
why a latency happened. Here is a typical trace.
|
|
|
|
# tracer: irqsoff
|
|
#
|
|
# irqsoff latency trace v1.1.5 on 3.8.0-test+
|
|
# --------------------------------------------------------------------
|
|
# latency: 259 us, #4/4, CPU#2 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
|
|
# -----------------
|
|
# | task: ps-6143 (uid:0 nice:0 policy:0 rt_prio:0)
|
|
# -----------------
|
|
# => started at: __lock_task_sighand
|
|
# => ended at: _raw_spin_unlock_irqrestore
|
|
#
|
|
#
|
|
# _------=> CPU#
|
|
# / _-----=> irqs-off
|
|
# | / _----=> need-resched
|
|
# || / _---=> hardirq/softirq
|
|
# ||| / _--=> preempt-depth
|
|
# |||| / delay
|
|
# cmd pid ||||| time | caller
|
|
# \ / ||||| \ | /
|
|
ps-6143 2d... 0us!: trace_hardirqs_off <-__lock_task_sighand
|
|
ps-6143 2d..1 259us+: trace_hardirqs_on <-_raw_spin_unlock_irqrestore
|
|
ps-6143 2d..1 263us+: time_hardirqs_on <-_raw_spin_unlock_irqrestore
|
|
ps-6143 2d..1 306us : <stack trace>
|
|
=> trace_hardirqs_on_caller
|
|
=> trace_hardirqs_on
|
|
=> _raw_spin_unlock_irqrestore
|
|
=> do_task_stat
|
|
=> proc_tgid_stat
|
|
=> proc_single_show
|
|
=> seq_read
|
|
=> vfs_read
|
|
=> sys_read
|
|
=> system_call_fastpath
|
|
|
|
|
|
This shows that the current tracer is "irqsoff" tracing the time
|
|
for which interrupts were disabled. It gives the trace version (which
|
|
never changes) and the version of the kernel upon which this was executed on
|
|
(3.10). Then it displays the max latency in microseconds (259 us). The number
|
|
of trace entries displayed and the total number (both are four: #4/4).
|
|
VP, KP, SP, and HP are always zero and are reserved for later use.
|
|
#P is the number of online CPUs (#P:4).
|
|
|
|
The task is the process that was running when the latency
|
|
occurred. (ps pid: 6143).
|
|
|
|
The start and stop (the functions in which the interrupts were
|
|
disabled and enabled respectively) that caused the latencies:
|
|
|
|
__lock_task_sighand is where the interrupts were disabled.
|
|
_raw_spin_unlock_irqrestore is where they were enabled again.
|
|
|
|
The next lines after the header are the trace itself. The header
|
|
explains which is which.
|
|
|
|
cmd: The name of the process in the trace.
|
|
|
|
pid: The PID of that process.
|
|
|
|
CPU#: The CPU which the process was running on.
|
|
|
|
irqs-off: 'd' interrupts are disabled. '.' otherwise.
|
|
Note: If the architecture does not support a way to
|
|
read the irq flags variable, an 'X' will always
|
|
be printed here.
|
|
|
|
need-resched:
|
|
'N' both TIF_NEED_RESCHED and PREEMPT_NEED_RESCHED is set,
|
|
'n' only TIF_NEED_RESCHED is set,
|
|
'p' only PREEMPT_NEED_RESCHED is set,
|
|
'.' otherwise.
|
|
|
|
hardirq/softirq:
|
|
'H' - hard irq occurred inside a softirq.
|
|
'h' - hard irq is running
|
|
's' - soft irq is running
|
|
'.' - normal context.
|
|
|
|
preempt-depth: The level of preempt_disabled
|
|
|
|
The above is mostly meaningful for kernel developers.
|
|
|
|
time: When the latency-format option is enabled, the trace file
|
|
output includes a timestamp relative to the start of the
|
|
trace. This differs from the output when latency-format
|
|
is disabled, which includes an absolute timestamp.
|
|
|
|
delay: This is just to help catch your eye a bit better. And
|
|
needs to be fixed to be only relative to the same CPU.
|
|
The marks are determined by the difference between this
|
|
current trace and the next trace.
|
|
'!' - greater than preempt_mark_thresh (default 100)
|
|
'+' - greater than 1 microsecond
|
|
' ' - less than or equal to 1 microsecond.
|
|
|
|
The rest is the same as the 'trace' file.
|
|
|
|
Note, the latency tracers will usually end with a back trace
|
|
to easily find where the latency occurred.
|
|
|
|
trace_options
|
|
-------------
|
|
|
|
The trace_options file (or the options directory) is used to control
|
|
what gets printed in the trace output, or manipulate the tracers.
|
|
To see what is available, simply cat the file:
|
|
|
|
cat trace_options
|
|
print-parent
|
|
nosym-offset
|
|
nosym-addr
|
|
noverbose
|
|
noraw
|
|
nohex
|
|
nobin
|
|
noblock
|
|
nostacktrace
|
|
trace_printk
|
|
noftrace_preempt
|
|
nobranch
|
|
annotate
|
|
nouserstacktrace
|
|
nosym-userobj
|
|
noprintk-msg-only
|
|
context-info
|
|
latency-format
|
|
sleep-time
|
|
graph-time
|
|
record-cmd
|
|
overwrite
|
|
nodisable_on_free
|
|
irq-info
|
|
markers
|
|
function-trace
|
|
|
|
To disable one of the options, echo in the option prepended with
|
|
"no".
|
|
|
|
echo noprint-parent > trace_options
|
|
|
|
To enable an option, leave off the "no".
|
|
|
|
echo sym-offset > trace_options
|
|
|
|
Here are the available options:
|
|
|
|
print-parent - On function traces, display the calling (parent)
|
|
function as well as the function being traced.
|
|
|
|
print-parent:
|
|
bash-4000 [01] 1477.606694: simple_strtoul <-kstrtoul
|
|
|
|
noprint-parent:
|
|
bash-4000 [01] 1477.606694: simple_strtoul
|
|
|
|
|
|
sym-offset - Display not only the function name, but also the
|
|
offset in the function. For example, instead of
|
|
seeing just "ktime_get", you will see
|
|
"ktime_get+0xb/0x20".
|
|
|
|
sym-offset:
|
|
bash-4000 [01] 1477.606694: simple_strtoul+0x6/0xa0
|
|
|
|
sym-addr - this will also display the function address as well
|
|
as the function name.
|
|
|
|
sym-addr:
|
|
bash-4000 [01] 1477.606694: simple_strtoul <c0339346>
|
|
|
|
verbose - This deals with the trace file when the
|
|
latency-format option is enabled.
|
|
|
|
bash 4000 1 0 00000000 00010a95 [58127d26] 1720.415ms \
|
|
(+0.000ms): simple_strtoul (kstrtoul)
|
|
|
|
raw - This will display raw numbers. This option is best for
|
|
use with user applications that can translate the raw
|
|
numbers better than having it done in the kernel.
|
|
|
|
hex - Similar to raw, but the numbers will be in a hexadecimal
|
|
format.
|
|
|
|
bin - This will print out the formats in raw binary.
|
|
|
|
block - When set, reading trace_pipe will not block when polled.
|
|
|
|
stacktrace - This is one of the options that changes the trace
|
|
itself. When a trace is recorded, so is the stack
|
|
of functions. This allows for back traces of
|
|
trace sites.
|
|
|
|
trace_printk - Can disable trace_printk() from writing into the buffer.
|
|
|
|
branch - Enable branch tracing with the tracer.
|
|
|
|
annotate - It is sometimes confusing when the CPU buffers are full
|
|
and one CPU buffer had a lot of events recently, thus
|
|
a shorter time frame, were another CPU may have only had
|
|
a few events, which lets it have older events. When
|
|
the trace is reported, it shows the oldest events first,
|
|
and it may look like only one CPU ran (the one with the
|
|
oldest events). When the annotate option is set, it will
|
|
display when a new CPU buffer started:
|
|
|
|
<idle>-0 [001] dNs4 21169.031481: wake_up_idle_cpu <-add_timer_on
|
|
<idle>-0 [001] dNs4 21169.031482: _raw_spin_unlock_irqrestore <-add_timer_on
|
|
<idle>-0 [001] .Ns4 21169.031484: sub_preempt_count <-_raw_spin_unlock_irqrestore
|
|
##### CPU 2 buffer started ####
|
|
<idle>-0 [002] .N.1 21169.031484: rcu_idle_exit <-cpu_idle
|
|
<idle>-0 [001] .Ns3 21169.031484: _raw_spin_unlock <-clocksource_watchdog
|
|
<idle>-0 [001] .Ns3 21169.031485: sub_preempt_count <-_raw_spin_unlock
|
|
|
|
userstacktrace - This option changes the trace. It records a
|
|
stacktrace of the current userspace thread.
|
|
|
|
sym-userobj - when user stacktrace are enabled, look up which
|
|
object the address belongs to, and print a
|
|
relative address. This is especially useful when
|
|
ASLR is on, otherwise you don't get a chance to
|
|
resolve the address to object/file/line after
|
|
the app is no longer running
|
|
|
|
The lookup is performed when you read
|
|
trace,trace_pipe. Example:
|
|
|
|
a.out-1623 [000] 40874.465068: /root/a.out[+0x480] <-/root/a.out[+0
|
|
x494] <- /root/a.out[+0x4a8] <- /lib/libc-2.7.so[+0x1e1a6]
|
|
|
|
|
|
printk-msg-only - When set, trace_printk()s will only show the format
|
|
and not their parameters (if trace_bprintk() or
|
|
trace_bputs() was used to save the trace_printk()).
|
|
|
|
context-info - Show only the event data. Hides the comm, PID,
|
|
timestamp, CPU, and other useful data.
|
|
|
|
latency-format - This option changes the trace. When
|
|
it is enabled, the trace displays
|
|
additional information about the
|
|
latencies, as described in "Latency
|
|
trace format".
|
|
|
|
sleep-time - When running function graph tracer, to include
|
|
the time a task schedules out in its function.
|
|
When enabled, it will account time the task has been
|
|
scheduled out as part of the function call.
|
|
|
|
graph-time - When running function graph tracer, to include the
|
|
time to call nested functions. When this is not set,
|
|
the time reported for the function will only include
|
|
the time the function itself executed for, not the time
|
|
for functions that it called.
|
|
|
|
record-cmd - When any event or tracer is enabled, a hook is enabled
|
|
in the sched_switch trace point to fill comm cache
|
|
with mapped pids and comms. But this may cause some
|
|
overhead, and if you only care about pids, and not the
|
|
name of the task, disabling this option can lower the
|
|
impact of tracing.
|
|
|
|
overwrite - This controls what happens when the trace buffer is
|
|
full. If "1" (default), the oldest events are
|
|
discarded and overwritten. If "0", then the newest
|
|
events are discarded.
|
|
(see per_cpu/cpu0/stats for overrun and dropped)
|
|
|
|
disable_on_free - When the free_buffer is closed, tracing will
|
|
stop (tracing_on set to 0).
|
|
|
|
irq-info - Shows the interrupt, preempt count, need resched data.
|
|
When disabled, the trace looks like:
|
|
|
|
# tracer: function
|
|
#
|
|
# entries-in-buffer/entries-written: 144405/9452052 #P:4
|
|
#
|
|
# TASK-PID CPU# TIMESTAMP FUNCTION
|
|
# | | | | |
|
|
<idle>-0 [002] 23636.756054: ttwu_do_activate.constprop.89 <-try_to_wake_up
|
|
<idle>-0 [002] 23636.756054: activate_task <-ttwu_do_activate.constprop.89
|
|
<idle>-0 [002] 23636.756055: enqueue_task <-activate_task
|
|
|
|
|
|
markers - When set, the trace_marker is writable (only by root).
|
|
When disabled, the trace_marker will error with EINVAL
|
|
on write.
|
|
|
|
|
|
function-trace - The latency tracers will enable function tracing
|
|
if this option is enabled (default it is). When
|
|
it is disabled, the latency tracers do not trace
|
|
functions. This keeps the overhead of the tracer down
|
|
when performing latency tests.
|
|
|
|
Note: Some tracers have their own options. They only appear
|
|
when the tracer is active.
|
|
|
|
|
|
|
|
irqsoff
|
|
-------
|
|
|
|
When interrupts are disabled, the CPU can not react to any other
|
|
external event (besides NMIs and SMIs). This prevents the timer
|
|
interrupt from triggering or the mouse interrupt from letting
|
|
the kernel know of a new mouse event. The result is a latency
|
|
with the reaction time.
|
|
|
|
The irqsoff tracer tracks the time for which interrupts are
|
|
disabled. When a new maximum latency is hit, the tracer saves
|
|
the trace leading up to that latency point so that every time a
|
|
new maximum is reached, the old saved trace is discarded and the
|
|
new trace is saved.
|
|
|
|
To reset the maximum, echo 0 into tracing_max_latency. Here is
|
|
an example:
|
|
|
|
# echo 0 > options/function-trace
|
|
# echo irqsoff > current_tracer
|
|
# echo 1 > tracing_on
|
|
# echo 0 > tracing_max_latency
|
|
# ls -ltr
|
|
[...]
|
|
# echo 0 > tracing_on
|
|
# cat trace
|
|
# tracer: irqsoff
|
|
#
|
|
# irqsoff latency trace v1.1.5 on 3.8.0-test+
|
|
# --------------------------------------------------------------------
|
|
# latency: 16 us, #4/4, CPU#0 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
|
|
# -----------------
|
|
# | task: swapper/0-0 (uid:0 nice:0 policy:0 rt_prio:0)
|
|
# -----------------
|
|
# => started at: run_timer_softirq
|
|
# => ended at: run_timer_softirq
|
|
#
|
|
#
|
|
# _------=> CPU#
|
|
# / _-----=> irqs-off
|
|
# | / _----=> need-resched
|
|
# || / _---=> hardirq/softirq
|
|
# ||| / _--=> preempt-depth
|
|
# |||| / delay
|
|
# cmd pid ||||| time | caller
|
|
# \ / ||||| \ | /
|
|
<idle>-0 0d.s2 0us+: _raw_spin_lock_irq <-run_timer_softirq
|
|
<idle>-0 0dNs3 17us : _raw_spin_unlock_irq <-run_timer_softirq
|
|
<idle>-0 0dNs3 17us+: trace_hardirqs_on <-run_timer_softirq
|
|
<idle>-0 0dNs3 25us : <stack trace>
|
|
=> _raw_spin_unlock_irq
|
|
=> run_timer_softirq
|
|
=> __do_softirq
|
|
=> call_softirq
|
|
=> do_softirq
|
|
=> irq_exit
|
|
=> smp_apic_timer_interrupt
|
|
=> apic_timer_interrupt
|
|
=> rcu_idle_exit
|
|
=> cpu_idle
|
|
=> rest_init
|
|
=> start_kernel
|
|
=> x86_64_start_reservations
|
|
=> x86_64_start_kernel
|
|
|
|
Here we see that that we had a latency of 16 microseconds (which is
|
|
very good). The _raw_spin_lock_irq in run_timer_softirq disabled
|
|
interrupts. The difference between the 16 and the displayed
|
|
timestamp 25us occurred because the clock was incremented
|
|
between the time of recording the max latency and the time of
|
|
recording the function that had that latency.
|
|
|
|
Note the above example had function-trace not set. If we set
|
|
function-trace, we get a much larger output:
|
|
|
|
with echo 1 > options/function-trace
|
|
|
|
# tracer: irqsoff
|
|
#
|
|
# irqsoff latency trace v1.1.5 on 3.8.0-test+
|
|
# --------------------------------------------------------------------
|
|
# latency: 71 us, #168/168, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
|
|
# -----------------
|
|
# | task: bash-2042 (uid:0 nice:0 policy:0 rt_prio:0)
|
|
# -----------------
|
|
# => started at: ata_scsi_queuecmd
|
|
# => ended at: ata_scsi_queuecmd
|
|
#
|
|
#
|
|
# _------=> CPU#
|
|
# / _-----=> irqs-off
|
|
# | / _----=> need-resched
|
|
# || / _---=> hardirq/softirq
|
|
# ||| / _--=> preempt-depth
|
|
# |||| / delay
|
|
# cmd pid ||||| time | caller
|
|
# \ / ||||| \ | /
|
|
bash-2042 3d... 0us : _raw_spin_lock_irqsave <-ata_scsi_queuecmd
|
|
bash-2042 3d... 0us : add_preempt_count <-_raw_spin_lock_irqsave
|
|
bash-2042 3d..1 1us : ata_scsi_find_dev <-ata_scsi_queuecmd
|
|
bash-2042 3d..1 1us : __ata_scsi_find_dev <-ata_scsi_find_dev
|
|
bash-2042 3d..1 2us : ata_find_dev.part.14 <-__ata_scsi_find_dev
|
|
bash-2042 3d..1 2us : ata_qc_new_init <-__ata_scsi_queuecmd
|
|
bash-2042 3d..1 3us : ata_sg_init <-__ata_scsi_queuecmd
|
|
bash-2042 3d..1 4us : ata_scsi_rw_xlat <-__ata_scsi_queuecmd
|
|
bash-2042 3d..1 4us : ata_build_rw_tf <-ata_scsi_rw_xlat
|
|
[...]
|
|
bash-2042 3d..1 67us : delay_tsc <-__delay
|
|
bash-2042 3d..1 67us : add_preempt_count <-delay_tsc
|
|
bash-2042 3d..2 67us : sub_preempt_count <-delay_tsc
|
|
bash-2042 3d..1 67us : add_preempt_count <-delay_tsc
|
|
bash-2042 3d..2 68us : sub_preempt_count <-delay_tsc
|
|
bash-2042 3d..1 68us+: ata_bmdma_start <-ata_bmdma_qc_issue
|
|
bash-2042 3d..1 71us : _raw_spin_unlock_irqrestore <-ata_scsi_queuecmd
|
|
bash-2042 3d..1 71us : _raw_spin_unlock_irqrestore <-ata_scsi_queuecmd
|
|
bash-2042 3d..1 72us+: trace_hardirqs_on <-ata_scsi_queuecmd
|
|
bash-2042 3d..1 120us : <stack trace>
|
|
=> _raw_spin_unlock_irqrestore
|
|
=> ata_scsi_queuecmd
|
|
=> scsi_dispatch_cmd
|
|
=> scsi_request_fn
|
|
=> __blk_run_queue_uncond
|
|
=> __blk_run_queue
|
|
=> blk_queue_bio
|
|
=> generic_make_request
|
|
=> submit_bio
|
|
=> submit_bh
|
|
=> __ext3_get_inode_loc
|
|
=> ext3_iget
|
|
=> ext3_lookup
|
|
=> lookup_real
|
|
=> __lookup_hash
|
|
=> walk_component
|
|
=> lookup_last
|
|
=> path_lookupat
|
|
=> filename_lookup
|
|
=> user_path_at_empty
|
|
=> user_path_at
|
|
=> vfs_fstatat
|
|
=> vfs_stat
|
|
=> sys_newstat
|
|
=> system_call_fastpath
|
|
|
|
|
|
Here we traced a 71 microsecond latency. But we also see all the
|
|
functions that were called during that time. Note that by
|
|
enabling function tracing, we incur an added overhead. This
|
|
overhead may extend the latency times. But nevertheless, this
|
|
trace has provided some very helpful debugging information.
|
|
|
|
|
|
preemptoff
|
|
----------
|
|
|
|
When preemption is disabled, we may be able to receive
|
|
interrupts but the task cannot be preempted and a higher
|
|
priority task must wait for preemption to be enabled again
|
|
before it can preempt a lower priority task.
|
|
|
|
The preemptoff tracer traces the places that disable preemption.
|
|
Like the irqsoff tracer, it records the maximum latency for
|
|
which preemption was disabled. The control of preemptoff tracer
|
|
is much like the irqsoff tracer.
|
|
|
|
# echo 0 > options/function-trace
|
|
# echo preemptoff > current_tracer
|
|
# echo 1 > tracing_on
|
|
# echo 0 > tracing_max_latency
|
|
# ls -ltr
|
|
[...]
|
|
# echo 0 > tracing_on
|
|
# cat trace
|
|
# tracer: preemptoff
|
|
#
|
|
# preemptoff latency trace v1.1.5 on 3.8.0-test+
|
|
# --------------------------------------------------------------------
|
|
# latency: 46 us, #4/4, CPU#1 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
|
|
# -----------------
|
|
# | task: sshd-1991 (uid:0 nice:0 policy:0 rt_prio:0)
|
|
# -----------------
|
|
# => started at: do_IRQ
|
|
# => ended at: do_IRQ
|
|
#
|
|
#
|
|
# _------=> CPU#
|
|
# / _-----=> irqs-off
|
|
# | / _----=> need-resched
|
|
# || / _---=> hardirq/softirq
|
|
# ||| / _--=> preempt-depth
|
|
# |||| / delay
|
|
# cmd pid ||||| time | caller
|
|
# \ / ||||| \ | /
|
|
sshd-1991 1d.h. 0us+: irq_enter <-do_IRQ
|
|
sshd-1991 1d..1 46us : irq_exit <-do_IRQ
|
|
sshd-1991 1d..1 47us+: trace_preempt_on <-do_IRQ
|
|
sshd-1991 1d..1 52us : <stack trace>
|
|
=> sub_preempt_count
|
|
=> irq_exit
|
|
=> do_IRQ
|
|
=> ret_from_intr
|
|
|
|
|
|
This has some more changes. Preemption was disabled when an
|
|
interrupt came in (notice the 'h'), and was enabled on exit.
|
|
But we also see that interrupts have been disabled when entering
|
|
the preempt off section and leaving it (the 'd'). We do not know if
|
|
interrupts were enabled in the mean time or shortly after this
|
|
was over.
|
|
|
|
# tracer: preemptoff
|
|
#
|
|
# preemptoff latency trace v1.1.5 on 3.8.0-test+
|
|
# --------------------------------------------------------------------
|
|
# latency: 83 us, #241/241, CPU#1 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
|
|
# -----------------
|
|
# | task: bash-1994 (uid:0 nice:0 policy:0 rt_prio:0)
|
|
# -----------------
|
|
# => started at: wake_up_new_task
|
|
# => ended at: task_rq_unlock
|
|
#
|
|
#
|
|
# _------=> CPU#
|
|
# / _-----=> irqs-off
|
|
# | / _----=> need-resched
|
|
# || / _---=> hardirq/softirq
|
|
# ||| / _--=> preempt-depth
|
|
# |||| / delay
|
|
# cmd pid ||||| time | caller
|
|
# \ / ||||| \ | /
|
|
bash-1994 1d..1 0us : _raw_spin_lock_irqsave <-wake_up_new_task
|
|
bash-1994 1d..1 0us : select_task_rq_fair <-select_task_rq
|
|
bash-1994 1d..1 1us : __rcu_read_lock <-select_task_rq_fair
|
|
bash-1994 1d..1 1us : source_load <-select_task_rq_fair
|
|
bash-1994 1d..1 1us : source_load <-select_task_rq_fair
|
|
[...]
|
|
bash-1994 1d..1 12us : irq_enter <-smp_apic_timer_interrupt
|
|
bash-1994 1d..1 12us : rcu_irq_enter <-irq_enter
|
|
bash-1994 1d..1 13us : add_preempt_count <-irq_enter
|
|
bash-1994 1d.h1 13us : exit_idle <-smp_apic_timer_interrupt
|
|
bash-1994 1d.h1 13us : hrtimer_interrupt <-smp_apic_timer_interrupt
|
|
bash-1994 1d.h1 13us : _raw_spin_lock <-hrtimer_interrupt
|
|
bash-1994 1d.h1 14us : add_preempt_count <-_raw_spin_lock
|
|
bash-1994 1d.h2 14us : ktime_get_update_offsets <-hrtimer_interrupt
|
|
[...]
|
|
bash-1994 1d.h1 35us : lapic_next_event <-clockevents_program_event
|
|
bash-1994 1d.h1 35us : irq_exit <-smp_apic_timer_interrupt
|
|
bash-1994 1d.h1 36us : sub_preempt_count <-irq_exit
|
|
bash-1994 1d..2 36us : do_softirq <-irq_exit
|
|
bash-1994 1d..2 36us : __do_softirq <-call_softirq
|
|
bash-1994 1d..2 36us : __local_bh_disable <-__do_softirq
|
|
bash-1994 1d.s2 37us : add_preempt_count <-_raw_spin_lock_irq
|
|
bash-1994 1d.s3 38us : _raw_spin_unlock <-run_timer_softirq
|
|
bash-1994 1d.s3 39us : sub_preempt_count <-_raw_spin_unlock
|
|
bash-1994 1d.s2 39us : call_timer_fn <-run_timer_softirq
|
|
[...]
|
|
bash-1994 1dNs2 81us : cpu_needs_another_gp <-rcu_process_callbacks
|
|
bash-1994 1dNs2 82us : __local_bh_enable <-__do_softirq
|
|
bash-1994 1dNs2 82us : sub_preempt_count <-__local_bh_enable
|
|
bash-1994 1dN.2 82us : idle_cpu <-irq_exit
|
|
bash-1994 1dN.2 83us : rcu_irq_exit <-irq_exit
|
|
bash-1994 1dN.2 83us : sub_preempt_count <-irq_exit
|
|
bash-1994 1.N.1 84us : _raw_spin_unlock_irqrestore <-task_rq_unlock
|
|
bash-1994 1.N.1 84us+: trace_preempt_on <-task_rq_unlock
|
|
bash-1994 1.N.1 104us : <stack trace>
|
|
=> sub_preempt_count
|
|
=> _raw_spin_unlock_irqrestore
|
|
=> task_rq_unlock
|
|
=> wake_up_new_task
|
|
=> do_fork
|
|
=> sys_clone
|
|
=> stub_clone
|
|
|
|
|
|
The above is an example of the preemptoff trace with
|
|
function-trace set. Here we see that interrupts were not disabled
|
|
the entire time. The irq_enter code lets us know that we entered
|
|
an interrupt 'h'. Before that, the functions being traced still
|
|
show that it is not in an interrupt, but we can see from the
|
|
functions themselves that this is not the case.
|
|
|
|
preemptirqsoff
|
|
--------------
|
|
|
|
Knowing the locations that have interrupts disabled or
|
|
preemption disabled for the longest times is helpful. But
|
|
sometimes we would like to know when either preemption and/or
|
|
interrupts are disabled.
|
|
|
|
Consider the following code:
|
|
|
|
local_irq_disable();
|
|
call_function_with_irqs_off();
|
|
preempt_disable();
|
|
call_function_with_irqs_and_preemption_off();
|
|
local_irq_enable();
|
|
call_function_with_preemption_off();
|
|
preempt_enable();
|
|
|
|
The irqsoff tracer will record the total length of
|
|
call_function_with_irqs_off() and
|
|
call_function_with_irqs_and_preemption_off().
|
|
|
|
The preemptoff tracer will record the total length of
|
|
call_function_with_irqs_and_preemption_off() and
|
|
call_function_with_preemption_off().
|
|
|
|
But neither will trace the time that interrupts and/or
|
|
preemption is disabled. This total time is the time that we can
|
|
not schedule. To record this time, use the preemptirqsoff
|
|
tracer.
|
|
|
|
Again, using this trace is much like the irqsoff and preemptoff
|
|
tracers.
|
|
|
|
# echo 0 > options/function-trace
|
|
# echo preemptirqsoff > current_tracer
|
|
# echo 1 > tracing_on
|
|
# echo 0 > tracing_max_latency
|
|
# ls -ltr
|
|
[...]
|
|
# echo 0 > tracing_on
|
|
# cat trace
|
|
# tracer: preemptirqsoff
|
|
#
|
|
# preemptirqsoff latency trace v1.1.5 on 3.8.0-test+
|
|
# --------------------------------------------------------------------
|
|
# latency: 100 us, #4/4, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
|
|
# -----------------
|
|
# | task: ls-2230 (uid:0 nice:0 policy:0 rt_prio:0)
|
|
# -----------------
|
|
# => started at: ata_scsi_queuecmd
|
|
# => ended at: ata_scsi_queuecmd
|
|
#
|
|
#
|
|
# _------=> CPU#
|
|
# / _-----=> irqs-off
|
|
# | / _----=> need-resched
|
|
# || / _---=> hardirq/softirq
|
|
# ||| / _--=> preempt-depth
|
|
# |||| / delay
|
|
# cmd pid ||||| time | caller
|
|
# \ / ||||| \ | /
|
|
ls-2230 3d... 0us+: _raw_spin_lock_irqsave <-ata_scsi_queuecmd
|
|
ls-2230 3...1 100us : _raw_spin_unlock_irqrestore <-ata_scsi_queuecmd
|
|
ls-2230 3...1 101us+: trace_preempt_on <-ata_scsi_queuecmd
|
|
ls-2230 3...1 111us : <stack trace>
|
|
=> sub_preempt_count
|
|
=> _raw_spin_unlock_irqrestore
|
|
=> ata_scsi_queuecmd
|
|
=> scsi_dispatch_cmd
|
|
=> scsi_request_fn
|
|
=> __blk_run_queue_uncond
|
|
=> __blk_run_queue
|
|
=> blk_queue_bio
|
|
=> generic_make_request
|
|
=> submit_bio
|
|
=> submit_bh
|
|
=> ext3_bread
|
|
=> ext3_dir_bread
|
|
=> htree_dirblock_to_tree
|
|
=> ext3_htree_fill_tree
|
|
=> ext3_readdir
|
|
=> vfs_readdir
|
|
=> sys_getdents
|
|
=> system_call_fastpath
|
|
|
|
|
|
The trace_hardirqs_off_thunk is called from assembly on x86 when
|
|
interrupts are disabled in the assembly code. Without the
|
|
function tracing, we do not know if interrupts were enabled
|
|
within the preemption points. We do see that it started with
|
|
preemption enabled.
|
|
|
|
Here is a trace with function-trace set:
|
|
|
|
# tracer: preemptirqsoff
|
|
#
|
|
# preemptirqsoff latency trace v1.1.5 on 3.8.0-test+
|
|
# --------------------------------------------------------------------
|
|
# latency: 161 us, #339/339, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
|
|
# -----------------
|
|
# | task: ls-2269 (uid:0 nice:0 policy:0 rt_prio:0)
|
|
# -----------------
|
|
# => started at: schedule
|
|
# => ended at: mutex_unlock
|
|
#
|
|
#
|
|
# _------=> CPU#
|
|
# / _-----=> irqs-off
|
|
# | / _----=> need-resched
|
|
# || / _---=> hardirq/softirq
|
|
# ||| / _--=> preempt-depth
|
|
# |||| / delay
|
|
# cmd pid ||||| time | caller
|
|
# \ / ||||| \ | /
|
|
kworker/-59 3...1 0us : __schedule <-schedule
|
|
kworker/-59 3d..1 0us : rcu_preempt_qs <-rcu_note_context_switch
|
|
kworker/-59 3d..1 1us : add_preempt_count <-_raw_spin_lock_irq
|
|
kworker/-59 3d..2 1us : deactivate_task <-__schedule
|
|
kworker/-59 3d..2 1us : dequeue_task <-deactivate_task
|
|
kworker/-59 3d..2 2us : update_rq_clock <-dequeue_task
|
|
kworker/-59 3d..2 2us : dequeue_task_fair <-dequeue_task
|
|
kworker/-59 3d..2 2us : update_curr <-dequeue_task_fair
|
|
kworker/-59 3d..2 2us : update_min_vruntime <-update_curr
|
|
kworker/-59 3d..2 3us : cpuacct_charge <-update_curr
|
|
kworker/-59 3d..2 3us : __rcu_read_lock <-cpuacct_charge
|
|
kworker/-59 3d..2 3us : __rcu_read_unlock <-cpuacct_charge
|
|
kworker/-59 3d..2 3us : update_cfs_rq_blocked_load <-dequeue_task_fair
|
|
kworker/-59 3d..2 4us : clear_buddies <-dequeue_task_fair
|
|
kworker/-59 3d..2 4us : account_entity_dequeue <-dequeue_task_fair
|
|
kworker/-59 3d..2 4us : update_min_vruntime <-dequeue_task_fair
|
|
kworker/-59 3d..2 4us : update_cfs_shares <-dequeue_task_fair
|
|
kworker/-59 3d..2 5us : hrtick_update <-dequeue_task_fair
|
|
kworker/-59 3d..2 5us : wq_worker_sleeping <-__schedule
|
|
kworker/-59 3d..2 5us : kthread_data <-wq_worker_sleeping
|
|
kworker/-59 3d..2 5us : put_prev_task_fair <-__schedule
|
|
kworker/-59 3d..2 6us : pick_next_task_fair <-pick_next_task
|
|
kworker/-59 3d..2 6us : clear_buddies <-pick_next_task_fair
|
|
kworker/-59 3d..2 6us : set_next_entity <-pick_next_task_fair
|
|
kworker/-59 3d..2 6us : update_stats_wait_end <-set_next_entity
|
|
ls-2269 3d..2 7us : finish_task_switch <-__schedule
|
|
ls-2269 3d..2 7us : _raw_spin_unlock_irq <-finish_task_switch
|
|
ls-2269 3d..2 8us : do_IRQ <-ret_from_intr
|
|
ls-2269 3d..2 8us : irq_enter <-do_IRQ
|
|
ls-2269 3d..2 8us : rcu_irq_enter <-irq_enter
|
|
ls-2269 3d..2 9us : add_preempt_count <-irq_enter
|
|
ls-2269 3d.h2 9us : exit_idle <-do_IRQ
|
|
[...]
|
|
ls-2269 3d.h3 20us : sub_preempt_count <-_raw_spin_unlock
|
|
ls-2269 3d.h2 20us : irq_exit <-do_IRQ
|
|
ls-2269 3d.h2 21us : sub_preempt_count <-irq_exit
|
|
ls-2269 3d..3 21us : do_softirq <-irq_exit
|
|
ls-2269 3d..3 21us : __do_softirq <-call_softirq
|
|
ls-2269 3d..3 21us+: __local_bh_disable <-__do_softirq
|
|
ls-2269 3d.s4 29us : sub_preempt_count <-_local_bh_enable_ip
|
|
ls-2269 3d.s5 29us : sub_preempt_count <-_local_bh_enable_ip
|
|
ls-2269 3d.s5 31us : do_IRQ <-ret_from_intr
|
|
ls-2269 3d.s5 31us : irq_enter <-do_IRQ
|
|
ls-2269 3d.s5 31us : rcu_irq_enter <-irq_enter
|
|
[...]
|
|
ls-2269 3d.s5 31us : rcu_irq_enter <-irq_enter
|
|
ls-2269 3d.s5 32us : add_preempt_count <-irq_enter
|
|
ls-2269 3d.H5 32us : exit_idle <-do_IRQ
|
|
ls-2269 3d.H5 32us : handle_irq <-do_IRQ
|
|
ls-2269 3d.H5 32us : irq_to_desc <-handle_irq
|
|
ls-2269 3d.H5 33us : handle_fasteoi_irq <-handle_irq
|
|
[...]
|
|
ls-2269 3d.s5 158us : _raw_spin_unlock_irqrestore <-rtl8139_poll
|
|
ls-2269 3d.s3 158us : net_rps_action_and_irq_enable.isra.65 <-net_rx_action
|
|
ls-2269 3d.s3 159us : __local_bh_enable <-__do_softirq
|
|
ls-2269 3d.s3 159us : sub_preempt_count <-__local_bh_enable
|
|
ls-2269 3d..3 159us : idle_cpu <-irq_exit
|
|
ls-2269 3d..3 159us : rcu_irq_exit <-irq_exit
|
|
ls-2269 3d..3 160us : sub_preempt_count <-irq_exit
|
|
ls-2269 3d... 161us : __mutex_unlock_slowpath <-mutex_unlock
|
|
ls-2269 3d... 162us+: trace_hardirqs_on <-mutex_unlock
|
|
ls-2269 3d... 186us : <stack trace>
|
|
=> __mutex_unlock_slowpath
|
|
=> mutex_unlock
|
|
=> process_output
|
|
=> n_tty_write
|
|
=> tty_write
|
|
=> vfs_write
|
|
=> sys_write
|
|
=> system_call_fastpath
|
|
|
|
This is an interesting trace. It started with kworker running and
|
|
scheduling out and ls taking over. But as soon as ls released the
|
|
rq lock and enabled interrupts (but not preemption) an interrupt
|
|
triggered. When the interrupt finished, it started running softirqs.
|
|
But while the softirq was running, another interrupt triggered.
|
|
When an interrupt is running inside a softirq, the annotation is 'H'.
|
|
|
|
|
|
wakeup
|
|
------
|
|
|
|
One common case that people are interested in tracing is the
|
|
time it takes for a task that is woken to actually wake up.
|
|
Now for non Real-Time tasks, this can be arbitrary. But tracing
|
|
it none the less can be interesting.
|
|
|
|
Without function tracing:
|
|
|
|
# echo 0 > options/function-trace
|
|
# echo wakeup > current_tracer
|
|
# echo 1 > tracing_on
|
|
# echo 0 > tracing_max_latency
|
|
# chrt -f 5 sleep 1
|
|
# echo 0 > tracing_on
|
|
# cat trace
|
|
# tracer: wakeup
|
|
#
|
|
# wakeup latency trace v1.1.5 on 3.8.0-test+
|
|
# --------------------------------------------------------------------
|
|
# latency: 15 us, #4/4, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
|
|
# -----------------
|
|
# | task: kworker/3:1H-312 (uid:0 nice:-20 policy:0 rt_prio:0)
|
|
# -----------------
|
|
#
|
|
# _------=> CPU#
|
|
# / _-----=> irqs-off
|
|
# | / _----=> need-resched
|
|
# || / _---=> hardirq/softirq
|
|
# ||| / _--=> preempt-depth
|
|
# |||| / delay
|
|
# cmd pid ||||| time | caller
|
|
# \ / ||||| \ | /
|
|
<idle>-0 3dNs7 0us : 0:120:R + [003] 312:100:R kworker/3:1H
|
|
<idle>-0 3dNs7 1us+: ttwu_do_activate.constprop.87 <-try_to_wake_up
|
|
<idle>-0 3d..3 15us : __schedule <-schedule
|
|
<idle>-0 3d..3 15us : 0:120:R ==> [003] 312:100:R kworker/3:1H
|
|
|
|
The tracer only traces the highest priority task in the system
|
|
to avoid tracing the normal circumstances. Here we see that
|
|
the kworker with a nice priority of -20 (not very nice), took
|
|
just 15 microseconds from the time it woke up, to the time it
|
|
ran.
|
|
|
|
Non Real-Time tasks are not that interesting. A more interesting
|
|
trace is to concentrate only on Real-Time tasks.
|
|
|
|
wakeup_rt
|
|
---------
|
|
|
|
In a Real-Time environment it is very important to know the
|
|
wakeup time it takes for the highest priority task that is woken
|
|
up to the time that it executes. This is also known as "schedule
|
|
latency". I stress the point that this is about RT tasks. It is
|
|
also important to know the scheduling latency of non-RT tasks,
|
|
but the average schedule latency is better for non-RT tasks.
|
|
Tools like LatencyTop are more appropriate for such
|
|
measurements.
|
|
|
|
Real-Time environments are interested in the worst case latency.
|
|
That is the longest latency it takes for something to happen,
|
|
and not the average. We can have a very fast scheduler that may
|
|
only have a large latency once in a while, but that would not
|
|
work well with Real-Time tasks. The wakeup_rt tracer was designed
|
|
to record the worst case wakeups of RT tasks. Non-RT tasks are
|
|
not recorded because the tracer only records one worst case and
|
|
tracing non-RT tasks that are unpredictable will overwrite the
|
|
worst case latency of RT tasks (just run the normal wakeup
|
|
tracer for a while to see that effect).
|
|
|
|
Since this tracer only deals with RT tasks, we will run this
|
|
slightly differently than we did with the previous tracers.
|
|
Instead of performing an 'ls', we will run 'sleep 1' under
|
|
'chrt' which changes the priority of the task.
|
|
|
|
# echo 0 > options/function-trace
|
|
# echo wakeup_rt > current_tracer
|
|
# echo 1 > tracing_on
|
|
# echo 0 > tracing_max_latency
|
|
# chrt -f 5 sleep 1
|
|
# echo 0 > tracing_on
|
|
# cat trace
|
|
# tracer: wakeup
|
|
#
|
|
# tracer: wakeup_rt
|
|
#
|
|
# wakeup_rt latency trace v1.1.5 on 3.8.0-test+
|
|
# --------------------------------------------------------------------
|
|
# latency: 5 us, #4/4, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
|
|
# -----------------
|
|
# | task: sleep-2389 (uid:0 nice:0 policy:1 rt_prio:5)
|
|
# -----------------
|
|
#
|
|
# _------=> CPU#
|
|
# / _-----=> irqs-off
|
|
# | / _----=> need-resched
|
|
# || / _---=> hardirq/softirq
|
|
# ||| / _--=> preempt-depth
|
|
# |||| / delay
|
|
# cmd pid ||||| time | caller
|
|
# \ / ||||| \ | /
|
|
<idle>-0 3d.h4 0us : 0:120:R + [003] 2389: 94:R sleep
|
|
<idle>-0 3d.h4 1us+: ttwu_do_activate.constprop.87 <-try_to_wake_up
|
|
<idle>-0 3d..3 5us : __schedule <-schedule
|
|
<idle>-0 3d..3 5us : 0:120:R ==> [003] 2389: 94:R sleep
|
|
|
|
|
|
Running this on an idle system, we see that it only took 5 microseconds
|
|
to perform the task switch. Note, since the trace point in the schedule
|
|
is before the actual "switch", we stop the tracing when the recorded task
|
|
is about to schedule in. This may change if we add a new marker at the
|
|
end of the scheduler.
|
|
|
|
Notice that the recorded task is 'sleep' with the PID of 2389
|
|
and it has an rt_prio of 5. This priority is user-space priority
|
|
and not the internal kernel priority. The policy is 1 for
|
|
SCHED_FIFO and 2 for SCHED_RR.
|
|
|
|
Note, that the trace data shows the internal priority (99 - rtprio).
|
|
|
|
<idle>-0 3d..3 5us : 0:120:R ==> [003] 2389: 94:R sleep
|
|
|
|
The 0:120:R means idle was running with a nice priority of 0 (120 - 20)
|
|
and in the running state 'R'. The sleep task was scheduled in with
|
|
2389: 94:R. That is the priority is the kernel rtprio (99 - 5 = 94)
|
|
and it too is in the running state.
|
|
|
|
Doing the same with chrt -r 5 and function-trace set.
|
|
|
|
echo 1 > options/function-trace
|
|
|
|
# tracer: wakeup_rt
|
|
#
|
|
# wakeup_rt latency trace v1.1.5 on 3.8.0-test+
|
|
# --------------------------------------------------------------------
|
|
# latency: 29 us, #85/85, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
|
|
# -----------------
|
|
# | task: sleep-2448 (uid:0 nice:0 policy:1 rt_prio:5)
|
|
# -----------------
|
|
#
|
|
# _------=> CPU#
|
|
# / _-----=> irqs-off
|
|
# | / _----=> need-resched
|
|
# || / _---=> hardirq/softirq
|
|
# ||| / _--=> preempt-depth
|
|
# |||| / delay
|
|
# cmd pid ||||| time | caller
|
|
# \ / ||||| \ | /
|
|
<idle>-0 3d.h4 1us+: 0:120:R + [003] 2448: 94:R sleep
|
|
<idle>-0 3d.h4 2us : ttwu_do_activate.constprop.87 <-try_to_wake_up
|
|
<idle>-0 3d.h3 3us : check_preempt_curr <-ttwu_do_wakeup
|
|
<idle>-0 3d.h3 3us : resched_task <-check_preempt_curr
|
|
<idle>-0 3dNh3 4us : task_woken_rt <-ttwu_do_wakeup
|
|
<idle>-0 3dNh3 4us : _raw_spin_unlock <-try_to_wake_up
|
|
<idle>-0 3dNh3 4us : sub_preempt_count <-_raw_spin_unlock
|
|
<idle>-0 3dNh2 5us : ttwu_stat <-try_to_wake_up
|
|
<idle>-0 3dNh2 5us : _raw_spin_unlock_irqrestore <-try_to_wake_up
|
|
<idle>-0 3dNh2 6us : sub_preempt_count <-_raw_spin_unlock_irqrestore
|
|
<idle>-0 3dNh1 6us : _raw_spin_lock <-__run_hrtimer
|
|
<idle>-0 3dNh1 6us : add_preempt_count <-_raw_spin_lock
|
|
<idle>-0 3dNh2 7us : _raw_spin_unlock <-hrtimer_interrupt
|
|
<idle>-0 3dNh2 7us : sub_preempt_count <-_raw_spin_unlock
|
|
<idle>-0 3dNh1 7us : tick_program_event <-hrtimer_interrupt
|
|
<idle>-0 3dNh1 7us : clockevents_program_event <-tick_program_event
|
|
<idle>-0 3dNh1 8us : ktime_get <-clockevents_program_event
|
|
<idle>-0 3dNh1 8us : lapic_next_event <-clockevents_program_event
|
|
<idle>-0 3dNh1 8us : irq_exit <-smp_apic_timer_interrupt
|
|
<idle>-0 3dNh1 9us : sub_preempt_count <-irq_exit
|
|
<idle>-0 3dN.2 9us : idle_cpu <-irq_exit
|
|
<idle>-0 3dN.2 9us : rcu_irq_exit <-irq_exit
|
|
<idle>-0 3dN.2 10us : rcu_eqs_enter_common.isra.45 <-rcu_irq_exit
|
|
<idle>-0 3dN.2 10us : sub_preempt_count <-irq_exit
|
|
<idle>-0 3.N.1 11us : rcu_idle_exit <-cpu_idle
|
|
<idle>-0 3dN.1 11us : rcu_eqs_exit_common.isra.43 <-rcu_idle_exit
|
|
<idle>-0 3.N.1 11us : tick_nohz_idle_exit <-cpu_idle
|
|
<idle>-0 3dN.1 12us : menu_hrtimer_cancel <-tick_nohz_idle_exit
|
|
<idle>-0 3dN.1 12us : ktime_get <-tick_nohz_idle_exit
|
|
<idle>-0 3dN.1 12us : tick_do_update_jiffies64 <-tick_nohz_idle_exit
|
|
<idle>-0 3dN.1 13us : update_cpu_load_nohz <-tick_nohz_idle_exit
|
|
<idle>-0 3dN.1 13us : _raw_spin_lock <-update_cpu_load_nohz
|
|
<idle>-0 3dN.1 13us : add_preempt_count <-_raw_spin_lock
|
|
<idle>-0 3dN.2 13us : __update_cpu_load <-update_cpu_load_nohz
|
|
<idle>-0 3dN.2 14us : sched_avg_update <-__update_cpu_load
|
|
<idle>-0 3dN.2 14us : _raw_spin_unlock <-update_cpu_load_nohz
|
|
<idle>-0 3dN.2 14us : sub_preempt_count <-_raw_spin_unlock
|
|
<idle>-0 3dN.1 15us : calc_load_exit_idle <-tick_nohz_idle_exit
|
|
<idle>-0 3dN.1 15us : touch_softlockup_watchdog <-tick_nohz_idle_exit
|
|
<idle>-0 3dN.1 15us : hrtimer_cancel <-tick_nohz_idle_exit
|
|
<idle>-0 3dN.1 15us : hrtimer_try_to_cancel <-hrtimer_cancel
|
|
<idle>-0 3dN.1 16us : lock_hrtimer_base.isra.18 <-hrtimer_try_to_cancel
|
|
<idle>-0 3dN.1 16us : _raw_spin_lock_irqsave <-lock_hrtimer_base.isra.18
|
|
<idle>-0 3dN.1 16us : add_preempt_count <-_raw_spin_lock_irqsave
|
|
<idle>-0 3dN.2 17us : __remove_hrtimer <-remove_hrtimer.part.16
|
|
<idle>-0 3dN.2 17us : hrtimer_force_reprogram <-__remove_hrtimer
|
|
<idle>-0 3dN.2 17us : tick_program_event <-hrtimer_force_reprogram
|
|
<idle>-0 3dN.2 18us : clockevents_program_event <-tick_program_event
|
|
<idle>-0 3dN.2 18us : ktime_get <-clockevents_program_event
|
|
<idle>-0 3dN.2 18us : lapic_next_event <-clockevents_program_event
|
|
<idle>-0 3dN.2 19us : _raw_spin_unlock_irqrestore <-hrtimer_try_to_cancel
|
|
<idle>-0 3dN.2 19us : sub_preempt_count <-_raw_spin_unlock_irqrestore
|
|
<idle>-0 3dN.1 19us : hrtimer_forward <-tick_nohz_idle_exit
|
|
<idle>-0 3dN.1 20us : ktime_add_safe <-hrtimer_forward
|
|
<idle>-0 3dN.1 20us : ktime_add_safe <-hrtimer_forward
|
|
<idle>-0 3dN.1 20us : hrtimer_start_range_ns <-hrtimer_start_expires.constprop.11
|
|
<idle>-0 3dN.1 20us : __hrtimer_start_range_ns <-hrtimer_start_range_ns
|
|
<idle>-0 3dN.1 21us : lock_hrtimer_base.isra.18 <-__hrtimer_start_range_ns
|
|
<idle>-0 3dN.1 21us : _raw_spin_lock_irqsave <-lock_hrtimer_base.isra.18
|
|
<idle>-0 3dN.1 21us : add_preempt_count <-_raw_spin_lock_irqsave
|
|
<idle>-0 3dN.2 22us : ktime_add_safe <-__hrtimer_start_range_ns
|
|
<idle>-0 3dN.2 22us : enqueue_hrtimer <-__hrtimer_start_range_ns
|
|
<idle>-0 3dN.2 22us : tick_program_event <-__hrtimer_start_range_ns
|
|
<idle>-0 3dN.2 23us : clockevents_program_event <-tick_program_event
|
|
<idle>-0 3dN.2 23us : ktime_get <-clockevents_program_event
|
|
<idle>-0 3dN.2 23us : lapic_next_event <-clockevents_program_event
|
|
<idle>-0 3dN.2 24us : _raw_spin_unlock_irqrestore <-__hrtimer_start_range_ns
|
|
<idle>-0 3dN.2 24us : sub_preempt_count <-_raw_spin_unlock_irqrestore
|
|
<idle>-0 3dN.1 24us : account_idle_ticks <-tick_nohz_idle_exit
|
|
<idle>-0 3dN.1 24us : account_idle_time <-account_idle_ticks
|
|
<idle>-0 3.N.1 25us : sub_preempt_count <-cpu_idle
|
|
<idle>-0 3.N.. 25us : schedule <-cpu_idle
|
|
<idle>-0 3.N.. 25us : __schedule <-preempt_schedule
|
|
<idle>-0 3.N.. 26us : add_preempt_count <-__schedule
|
|
<idle>-0 3.N.1 26us : rcu_note_context_switch <-__schedule
|
|
<idle>-0 3.N.1 26us : rcu_sched_qs <-rcu_note_context_switch
|
|
<idle>-0 3dN.1 27us : rcu_preempt_qs <-rcu_note_context_switch
|
|
<idle>-0 3.N.1 27us : _raw_spin_lock_irq <-__schedule
|
|
<idle>-0 3dN.1 27us : add_preempt_count <-_raw_spin_lock_irq
|
|
<idle>-0 3dN.2 28us : put_prev_task_idle <-__schedule
|
|
<idle>-0 3dN.2 28us : pick_next_task_stop <-pick_next_task
|
|
<idle>-0 3dN.2 28us : pick_next_task_rt <-pick_next_task
|
|
<idle>-0 3dN.2 29us : dequeue_pushable_task <-pick_next_task_rt
|
|
<idle>-0 3d..3 29us : __schedule <-preempt_schedule
|
|
<idle>-0 3d..3 30us : 0:120:R ==> [003] 2448: 94:R sleep
|
|
|
|
This isn't that big of a trace, even with function tracing enabled,
|
|
so I included the entire trace.
|
|
|
|
The interrupt went off while when the system was idle. Somewhere
|
|
before task_woken_rt() was called, the NEED_RESCHED flag was set,
|
|
this is indicated by the first occurrence of the 'N' flag.
|
|
|
|
Latency tracing and events
|
|
--------------------------
|
|
As function tracing can induce a much larger latency, but without
|
|
seeing what happens within the latency it is hard to know what
|
|
caused it. There is a middle ground, and that is with enabling
|
|
events.
|
|
|
|
# echo 0 > options/function-trace
|
|
# echo wakeup_rt > current_tracer
|
|
# echo 1 > events/enable
|
|
# echo 1 > tracing_on
|
|
# echo 0 > tracing_max_latency
|
|
# chrt -f 5 sleep 1
|
|
# echo 0 > tracing_on
|
|
# cat trace
|
|
# tracer: wakeup_rt
|
|
#
|
|
# wakeup_rt latency trace v1.1.5 on 3.8.0-test+
|
|
# --------------------------------------------------------------------
|
|
# latency: 6 us, #12/12, CPU#2 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
|
|
# -----------------
|
|
# | task: sleep-5882 (uid:0 nice:0 policy:1 rt_prio:5)
|
|
# -----------------
|
|
#
|
|
# _------=> CPU#
|
|
# / _-----=> irqs-off
|
|
# | / _----=> need-resched
|
|
# || / _---=> hardirq/softirq
|
|
# ||| / _--=> preempt-depth
|
|
# |||| / delay
|
|
# cmd pid ||||| time | caller
|
|
# \ / ||||| \ | /
|
|
<idle>-0 2d.h4 0us : 0:120:R + [002] 5882: 94:R sleep
|
|
<idle>-0 2d.h4 0us : ttwu_do_activate.constprop.87 <-try_to_wake_up
|
|
<idle>-0 2d.h4 1us : sched_wakeup: comm=sleep pid=5882 prio=94 success=1 target_cpu=002
|
|
<idle>-0 2dNh2 1us : hrtimer_expire_exit: hrtimer=ffff88007796feb8
|
|
<idle>-0 2.N.2 2us : power_end: cpu_id=2
|
|
<idle>-0 2.N.2 3us : cpu_idle: state=4294967295 cpu_id=2
|
|
<idle>-0 2dN.3 4us : hrtimer_cancel: hrtimer=ffff88007d50d5e0
|
|
<idle>-0 2dN.3 4us : hrtimer_start: hrtimer=ffff88007d50d5e0 function=tick_sched_timer expires=34311211000000 softexpires=34311211000000
|
|
<idle>-0 2.N.2 5us : rcu_utilization: Start context switch
|
|
<idle>-0 2.N.2 5us : rcu_utilization: End context switch
|
|
<idle>-0 2d..3 6us : __schedule <-schedule
|
|
<idle>-0 2d..3 6us : 0:120:R ==> [002] 5882: 94:R sleep
|
|
|
|
|
|
function
|
|
--------
|
|
|
|
This tracer is the function tracer. Enabling the function tracer
|
|
can be done from the debug file system. Make sure the
|
|
ftrace_enabled is set; otherwise this tracer is a nop.
|
|
See the "ftrace_enabled" section below.
|
|
|
|
# sysctl kernel.ftrace_enabled=1
|
|
# echo function > current_tracer
|
|
# echo 1 > tracing_on
|
|
# usleep 1
|
|
# echo 0 > tracing_on
|
|
# cat trace
|
|
# tracer: function
|
|
#
|
|
# entries-in-buffer/entries-written: 24799/24799 #P:4
|
|
#
|
|
# _-----=> irqs-off
|
|
# / _----=> need-resched
|
|
# | / _---=> hardirq/softirq
|
|
# || / _--=> preempt-depth
|
|
# ||| / delay
|
|
# TASK-PID CPU# |||| TIMESTAMP FUNCTION
|
|
# | | | |||| | |
|
|
bash-1994 [002] .... 3082.063030: mutex_unlock <-rb_simple_write
|
|
bash-1994 [002] .... 3082.063031: __mutex_unlock_slowpath <-mutex_unlock
|
|
bash-1994 [002] .... 3082.063031: __fsnotify_parent <-fsnotify_modify
|
|
bash-1994 [002] .... 3082.063032: fsnotify <-fsnotify_modify
|
|
bash-1994 [002] .... 3082.063032: __srcu_read_lock <-fsnotify
|
|
bash-1994 [002] .... 3082.063032: add_preempt_count <-__srcu_read_lock
|
|
bash-1994 [002] ...1 3082.063032: sub_preempt_count <-__srcu_read_lock
|
|
bash-1994 [002] .... 3082.063033: __srcu_read_unlock <-fsnotify
|
|
[...]
|
|
|
|
|
|
Note: function tracer uses ring buffers to store the above
|
|
entries. The newest data may overwrite the oldest data.
|
|
Sometimes using echo to stop the trace is not sufficient because
|
|
the tracing could have overwritten the data that you wanted to
|
|
record. For this reason, it is sometimes better to disable
|
|
tracing directly from a program. This allows you to stop the
|
|
tracing at the point that you hit the part that you are
|
|
interested in. To disable the tracing directly from a C program,
|
|
something like following code snippet can be used:
|
|
|
|
int trace_fd;
|
|
[...]
|
|
int main(int argc, char *argv[]) {
|
|
[...]
|
|
trace_fd = open(tracing_file("tracing_on"), O_WRONLY);
|
|
[...]
|
|
if (condition_hit()) {
|
|
write(trace_fd, "0", 1);
|
|
}
|
|
[...]
|
|
}
|
|
|
|
|
|
Single thread tracing
|
|
---------------------
|
|
|
|
By writing into set_ftrace_pid you can trace a
|
|
single thread. For example:
|
|
|
|
# cat set_ftrace_pid
|
|
no pid
|
|
# echo 3111 > set_ftrace_pid
|
|
# cat set_ftrace_pid
|
|
3111
|
|
# echo function > current_tracer
|
|
# cat trace | head
|
|
# tracer: function
|
|
#
|
|
# TASK-PID CPU# TIMESTAMP FUNCTION
|
|
# | | | | |
|
|
yum-updatesd-3111 [003] 1637.254676: finish_task_switch <-thread_return
|
|
yum-updatesd-3111 [003] 1637.254681: hrtimer_cancel <-schedule_hrtimeout_range
|
|
yum-updatesd-3111 [003] 1637.254682: hrtimer_try_to_cancel <-hrtimer_cancel
|
|
yum-updatesd-3111 [003] 1637.254683: lock_hrtimer_base <-hrtimer_try_to_cancel
|
|
yum-updatesd-3111 [003] 1637.254685: fget_light <-do_sys_poll
|
|
yum-updatesd-3111 [003] 1637.254686: pipe_poll <-do_sys_poll
|
|
# echo -1 > set_ftrace_pid
|
|
# cat trace |head
|
|
# tracer: function
|
|
#
|
|
# TASK-PID CPU# TIMESTAMP FUNCTION
|
|
# | | | | |
|
|
##### CPU 3 buffer started ####
|
|
yum-updatesd-3111 [003] 1701.957688: free_poll_entry <-poll_freewait
|
|
yum-updatesd-3111 [003] 1701.957689: remove_wait_queue <-free_poll_entry
|
|
yum-updatesd-3111 [003] 1701.957691: fput <-free_poll_entry
|
|
yum-updatesd-3111 [003] 1701.957692: audit_syscall_exit <-sysret_audit
|
|
yum-updatesd-3111 [003] 1701.957693: path_put <-audit_syscall_exit
|
|
|
|
If you want to trace a function when executing, you could use
|
|
something like this simple program:
|
|
|
|
#include <stdio.h>
|
|
#include <stdlib.h>
|
|
#include <sys/types.h>
|
|
#include <sys/stat.h>
|
|
#include <fcntl.h>
|
|
#include <unistd.h>
|
|
#include <string.h>
|
|
|
|
#define _STR(x) #x
|
|
#define STR(x) _STR(x)
|
|
#define MAX_PATH 256
|
|
|
|
const char *find_debugfs(void)
|
|
{
|
|
static char debugfs[MAX_PATH+1];
|
|
static int debugfs_found;
|
|
char type[100];
|
|
FILE *fp;
|
|
|
|
if (debugfs_found)
|
|
return debugfs;
|
|
|
|
if ((fp = fopen("/proc/mounts","r")) == NULL) {
|
|
perror("/proc/mounts");
|
|
return NULL;
|
|
}
|
|
|
|
while (fscanf(fp, "%*s %"
|
|
STR(MAX_PATH)
|
|
"s %99s %*s %*d %*d\n",
|
|
debugfs, type) == 2) {
|
|
if (strcmp(type, "debugfs") == 0)
|
|
break;
|
|
}
|
|
fclose(fp);
|
|
|
|
if (strcmp(type, "debugfs") != 0) {
|
|
fprintf(stderr, "debugfs not mounted");
|
|
return NULL;
|
|
}
|
|
|
|
strcat(debugfs, "/tracing/");
|
|
debugfs_found = 1;
|
|
|
|
return debugfs;
|
|
}
|
|
|
|
const char *tracing_file(const char *file_name)
|
|
{
|
|
static char trace_file[MAX_PATH+1];
|
|
snprintf(trace_file, MAX_PATH, "%s/%s", find_debugfs(), file_name);
|
|
return trace_file;
|
|
}
|
|
|
|
int main (int argc, char **argv)
|
|
{
|
|
if (argc < 1)
|
|
exit(-1);
|
|
|
|
if (fork() > 0) {
|
|
int fd, ffd;
|
|
char line[64];
|
|
int s;
|
|
|
|
ffd = open(tracing_file("current_tracer"), O_WRONLY);
|
|
if (ffd < 0)
|
|
exit(-1);
|
|
write(ffd, "nop", 3);
|
|
|
|
fd = open(tracing_file("set_ftrace_pid"), O_WRONLY);
|
|
s = sprintf(line, "%d\n", getpid());
|
|
write(fd, line, s);
|
|
|
|
write(ffd, "function", 8);
|
|
|
|
close(fd);
|
|
close(ffd);
|
|
|
|
execvp(argv[1], argv+1);
|
|
}
|
|
|
|
return 0;
|
|
}
|
|
|
|
Or this simple script!
|
|
|
|
------
|
|
#!/bin/bash
|
|
|
|
debugfs=`sed -ne 's/^debugfs \(.*\) debugfs.*/\1/p' /proc/mounts`
|
|
echo nop > $debugfs/tracing/current_tracer
|
|
echo 0 > $debugfs/tracing/tracing_on
|
|
echo $$ > $debugfs/tracing/set_ftrace_pid
|
|
echo function > $debugfs/tracing/current_tracer
|
|
echo 1 > $debugfs/tracing/tracing_on
|
|
exec "$@"
|
|
------
|
|
|
|
|
|
function graph tracer
|
|
---------------------------
|
|
|
|
This tracer is similar to the function tracer except that it
|
|
probes a function on its entry and its exit. This is done by
|
|
using a dynamically allocated stack of return addresses in each
|
|
task_struct. On function entry the tracer overwrites the return
|
|
address of each function traced to set a custom probe. Thus the
|
|
original return address is stored on the stack of return address
|
|
in the task_struct.
|
|
|
|
Probing on both ends of a function leads to special features
|
|
such as:
|
|
|
|
- measure of a function's time execution
|
|
- having a reliable call stack to draw function calls graph
|
|
|
|
This tracer is useful in several situations:
|
|
|
|
- you want to find the reason of a strange kernel behavior and
|
|
need to see what happens in detail on any areas (or specific
|
|
ones).
|
|
|
|
- you are experiencing weird latencies but it's difficult to
|
|
find its origin.
|
|
|
|
- you want to find quickly which path is taken by a specific
|
|
function
|
|
|
|
- you just want to peek inside a working kernel and want to see
|
|
what happens there.
|
|
|
|
# tracer: function_graph
|
|
#
|
|
# CPU DURATION FUNCTION CALLS
|
|
# | | | | | | |
|
|
|
|
0) | sys_open() {
|
|
0) | do_sys_open() {
|
|
0) | getname() {
|
|
0) | kmem_cache_alloc() {
|
|
0) 1.382 us | __might_sleep();
|
|
0) 2.478 us | }
|
|
0) | strncpy_from_user() {
|
|
0) | might_fault() {
|
|
0) 1.389 us | __might_sleep();
|
|
0) 2.553 us | }
|
|
0) 3.807 us | }
|
|
0) 7.876 us | }
|
|
0) | alloc_fd() {
|
|
0) 0.668 us | _spin_lock();
|
|
0) 0.570 us | expand_files();
|
|
0) 0.586 us | _spin_unlock();
|
|
|
|
|
|
There are several columns that can be dynamically
|
|
enabled/disabled. You can use every combination of options you
|
|
want, depending on your needs.
|
|
|
|
- The cpu number on which the function executed is default
|
|
enabled. It is sometimes better to only trace one cpu (see
|
|
tracing_cpu_mask file) or you might sometimes see unordered
|
|
function calls while cpu tracing switch.
|
|
|
|
hide: echo nofuncgraph-cpu > trace_options
|
|
show: echo funcgraph-cpu > trace_options
|
|
|
|
- The duration (function's time of execution) is displayed on
|
|
the closing bracket line of a function or on the same line
|
|
than the current function in case of a leaf one. It is default
|
|
enabled.
|
|
|
|
hide: echo nofuncgraph-duration > trace_options
|
|
show: echo funcgraph-duration > trace_options
|
|
|
|
- The overhead field precedes the duration field in case of
|
|
reached duration thresholds.
|
|
|
|
hide: echo nofuncgraph-overhead > trace_options
|
|
show: echo funcgraph-overhead > trace_options
|
|
depends on: funcgraph-duration
|
|
|
|
ie:
|
|
|
|
0) | up_write() {
|
|
0) 0.646 us | _spin_lock_irqsave();
|
|
0) 0.684 us | _spin_unlock_irqrestore();
|
|
0) 3.123 us | }
|
|
0) 0.548 us | fput();
|
|
0) + 58.628 us | }
|
|
|
|
[...]
|
|
|
|
0) | putname() {
|
|
0) | kmem_cache_free() {
|
|
0) 0.518 us | __phys_addr();
|
|
0) 1.757 us | }
|
|
0) 2.861 us | }
|
|
0) ! 115.305 us | }
|
|
0) ! 116.402 us | }
|
|
|
|
+ means that the function exceeded 10 usecs.
|
|
! means that the function exceeded 100 usecs.
|
|
|
|
|
|
- The task/pid field displays the thread cmdline and pid which
|
|
executed the function. It is default disabled.
|
|
|
|
hide: echo nofuncgraph-proc > trace_options
|
|
show: echo funcgraph-proc > trace_options
|
|
|
|
ie:
|
|
|
|
# tracer: function_graph
|
|
#
|
|
# CPU TASK/PID DURATION FUNCTION CALLS
|
|
# | | | | | | | | |
|
|
0) sh-4802 | | d_free() {
|
|
0) sh-4802 | | call_rcu() {
|
|
0) sh-4802 | | __call_rcu() {
|
|
0) sh-4802 | 0.616 us | rcu_process_gp_end();
|
|
0) sh-4802 | 0.586 us | check_for_new_grace_period();
|
|
0) sh-4802 | 2.899 us | }
|
|
0) sh-4802 | 4.040 us | }
|
|
0) sh-4802 | 5.151 us | }
|
|
0) sh-4802 | + 49.370 us | }
|
|
|
|
|
|
- The absolute time field is an absolute timestamp given by the
|
|
system clock since it started. A snapshot of this time is
|
|
given on each entry/exit of functions
|
|
|
|
hide: echo nofuncgraph-abstime > trace_options
|
|
show: echo funcgraph-abstime > trace_options
|
|
|
|
ie:
|
|
|
|
#
|
|
# TIME CPU DURATION FUNCTION CALLS
|
|
# | | | | | | | |
|
|
360.774522 | 1) 0.541 us | }
|
|
360.774522 | 1) 4.663 us | }
|
|
360.774523 | 1) 0.541 us | __wake_up_bit();
|
|
360.774524 | 1) 6.796 us | }
|
|
360.774524 | 1) 7.952 us | }
|
|
360.774525 | 1) 9.063 us | }
|
|
360.774525 | 1) 0.615 us | journal_mark_dirty();
|
|
360.774527 | 1) 0.578 us | __brelse();
|
|
360.774528 | 1) | reiserfs_prepare_for_journal() {
|
|
360.774528 | 1) | unlock_buffer() {
|
|
360.774529 | 1) | wake_up_bit() {
|
|
360.774529 | 1) | bit_waitqueue() {
|
|
360.774530 | 1) 0.594 us | __phys_addr();
|
|
|
|
|
|
You can put some comments on specific functions by using
|
|
trace_printk() For example, if you want to put a comment inside
|
|
the __might_sleep() function, you just have to include
|
|
<linux/ftrace.h> and call trace_printk() inside __might_sleep()
|
|
|
|
trace_printk("I'm a comment!\n")
|
|
|
|
will produce:
|
|
|
|
1) | __might_sleep() {
|
|
1) | /* I'm a comment! */
|
|
1) 1.449 us | }
|
|
|
|
|
|
You might find other useful features for this tracer in the
|
|
following "dynamic ftrace" section such as tracing only specific
|
|
functions or tasks.
|
|
|
|
dynamic ftrace
|
|
--------------
|
|
|
|
If CONFIG_DYNAMIC_FTRACE is set, the system will run with
|
|
virtually no overhead when function tracing is disabled. The way
|
|
this works is the mcount function call (placed at the start of
|
|
every kernel function, produced by the -pg switch in gcc),
|
|
starts of pointing to a simple return. (Enabling FTRACE will
|
|
include the -pg switch in the compiling of the kernel.)
|
|
|
|
At compile time every C file object is run through the
|
|
recordmcount program (located in the scripts directory). This
|
|
program will parse the ELF headers in the C object to find all
|
|
the locations in the .text section that call mcount. (Note, only
|
|
white listed .text sections are processed, since processing other
|
|
sections like .init.text may cause races due to those sections
|
|
being freed unexpectedly).
|
|
|
|
A new section called "__mcount_loc" is created that holds
|
|
references to all the mcount call sites in the .text section.
|
|
The recordmcount program re-links this section back into the
|
|
original object. The final linking stage of the kernel will add all these
|
|
references into a single table.
|
|
|
|
On boot up, before SMP is initialized, the dynamic ftrace code
|
|
scans this table and updates all the locations into nops. It
|
|
also records the locations, which are added to the
|
|
available_filter_functions list. Modules are processed as they
|
|
are loaded and before they are executed. When a module is
|
|
unloaded, it also removes its functions from the ftrace function
|
|
list. This is automatic in the module unload code, and the
|
|
module author does not need to worry about it.
|
|
|
|
When tracing is enabled, the process of modifying the function
|
|
tracepoints is dependent on architecture. The old method is to use
|
|
kstop_machine to prevent races with the CPUs executing code being
|
|
modified (which can cause the CPU to do undesirable things, especially
|
|
if the modified code crosses cache (or page) boundaries), and the nops are
|
|
patched back to calls. But this time, they do not call mcount
|
|
(which is just a function stub). They now call into the ftrace
|
|
infrastructure.
|
|
|
|
The new method of modifying the function tracepoints is to place
|
|
a breakpoint at the location to be modified, sync all CPUs, modify
|
|
the rest of the instruction not covered by the breakpoint. Sync
|
|
all CPUs again, and then remove the breakpoint with the finished
|
|
version to the ftrace call site.
|
|
|
|
Some archs do not even need to monkey around with the synchronization,
|
|
and can just slap the new code on top of the old without any
|
|
problems with other CPUs executing it at the same time.
|
|
|
|
One special side-effect to the recording of the functions being
|
|
traced is that we can now selectively choose which functions we
|
|
wish to trace and which ones we want the mcount calls to remain
|
|
as nops.
|
|
|
|
Two files are used, one for enabling and one for disabling the
|
|
tracing of specified functions. They are:
|
|
|
|
set_ftrace_filter
|
|
|
|
and
|
|
|
|
set_ftrace_notrace
|
|
|
|
A list of available functions that you can add to these files is
|
|
listed in:
|
|
|
|
available_filter_functions
|
|
|
|
# cat available_filter_functions
|
|
put_prev_task_idle
|
|
kmem_cache_create
|
|
pick_next_task_rt
|
|
get_online_cpus
|
|
pick_next_task_fair
|
|
mutex_lock
|
|
[...]
|
|
|
|
If I am only interested in sys_nanosleep and hrtimer_interrupt:
|
|
|
|
# echo sys_nanosleep hrtimer_interrupt > set_ftrace_filter
|
|
# echo function > current_tracer
|
|
# echo 1 > tracing_on
|
|
# usleep 1
|
|
# echo 0 > tracing_on
|
|
# cat trace
|
|
# tracer: function
|
|
#
|
|
# entries-in-buffer/entries-written: 5/5 #P:4
|
|
#
|
|
# _-----=> irqs-off
|
|
# / _----=> need-resched
|
|
# | / _---=> hardirq/softirq
|
|
# || / _--=> preempt-depth
|
|
# ||| / delay
|
|
# TASK-PID CPU# |||| TIMESTAMP FUNCTION
|
|
# | | | |||| | |
|
|
usleep-2665 [001] .... 4186.475355: sys_nanosleep <-system_call_fastpath
|
|
<idle>-0 [001] d.h1 4186.475409: hrtimer_interrupt <-smp_apic_timer_interrupt
|
|
usleep-2665 [001] d.h1 4186.475426: hrtimer_interrupt <-smp_apic_timer_interrupt
|
|
<idle>-0 [003] d.h1 4186.475426: hrtimer_interrupt <-smp_apic_timer_interrupt
|
|
<idle>-0 [002] d.h1 4186.475427: hrtimer_interrupt <-smp_apic_timer_interrupt
|
|
|
|
To see which functions are being traced, you can cat the file:
|
|
|
|
# cat set_ftrace_filter
|
|
hrtimer_interrupt
|
|
sys_nanosleep
|
|
|
|
|
|
Perhaps this is not enough. The filters also allow simple wild
|
|
cards. Only the following are currently available
|
|
|
|
<match>* - will match functions that begin with <match>
|
|
*<match> - will match functions that end with <match>
|
|
*<match>* - will match functions that have <match> in it
|
|
|
|
These are the only wild cards which are supported.
|
|
|
|
<match>*<match> will not work.
|
|
|
|
Note: It is better to use quotes to enclose the wild cards,
|
|
otherwise the shell may expand the parameters into names
|
|
of files in the local directory.
|
|
|
|
# echo 'hrtimer_*' > set_ftrace_filter
|
|
|
|
Produces:
|
|
|
|
# tracer: function
|
|
#
|
|
# entries-in-buffer/entries-written: 897/897 #P:4
|
|
#
|
|
# _-----=> irqs-off
|
|
# / _----=> need-resched
|
|
# | / _---=> hardirq/softirq
|
|
# || / _--=> preempt-depth
|
|
# ||| / delay
|
|
# TASK-PID CPU# |||| TIMESTAMP FUNCTION
|
|
# | | | |||| | |
|
|
<idle>-0 [003] dN.1 4228.547803: hrtimer_cancel <-tick_nohz_idle_exit
|
|
<idle>-0 [003] dN.1 4228.547804: hrtimer_try_to_cancel <-hrtimer_cancel
|
|
<idle>-0 [003] dN.2 4228.547805: hrtimer_force_reprogram <-__remove_hrtimer
|
|
<idle>-0 [003] dN.1 4228.547805: hrtimer_forward <-tick_nohz_idle_exit
|
|
<idle>-0 [003] dN.1 4228.547805: hrtimer_start_range_ns <-hrtimer_start_expires.constprop.11
|
|
<idle>-0 [003] d..1 4228.547858: hrtimer_get_next_event <-get_next_timer_interrupt
|
|
<idle>-0 [003] d..1 4228.547859: hrtimer_start <-__tick_nohz_idle_enter
|
|
<idle>-0 [003] d..2 4228.547860: hrtimer_force_reprogram <-__rem
|
|
|
|
Notice that we lost the sys_nanosleep.
|
|
|
|
# cat set_ftrace_filter
|
|
hrtimer_run_queues
|
|
hrtimer_run_pending
|
|
hrtimer_init
|
|
hrtimer_cancel
|
|
hrtimer_try_to_cancel
|
|
hrtimer_forward
|
|
hrtimer_start
|
|
hrtimer_reprogram
|
|
hrtimer_force_reprogram
|
|
hrtimer_get_next_event
|
|
hrtimer_interrupt
|
|
hrtimer_nanosleep
|
|
hrtimer_wakeup
|
|
hrtimer_get_remaining
|
|
hrtimer_get_res
|
|
hrtimer_init_sleeper
|
|
|
|
|
|
This is because the '>' and '>>' act just like they do in bash.
|
|
To rewrite the filters, use '>'
|
|
To append to the filters, use '>>'
|
|
|
|
To clear out a filter so that all functions will be recorded
|
|
again:
|
|
|
|
# echo > set_ftrace_filter
|
|
# cat set_ftrace_filter
|
|
#
|
|
|
|
Again, now we want to append.
|
|
|
|
# echo sys_nanosleep > set_ftrace_filter
|
|
# cat set_ftrace_filter
|
|
sys_nanosleep
|
|
# echo 'hrtimer_*' >> set_ftrace_filter
|
|
# cat set_ftrace_filter
|
|
hrtimer_run_queues
|
|
hrtimer_run_pending
|
|
hrtimer_init
|
|
hrtimer_cancel
|
|
hrtimer_try_to_cancel
|
|
hrtimer_forward
|
|
hrtimer_start
|
|
hrtimer_reprogram
|
|
hrtimer_force_reprogram
|
|
hrtimer_get_next_event
|
|
hrtimer_interrupt
|
|
sys_nanosleep
|
|
hrtimer_nanosleep
|
|
hrtimer_wakeup
|
|
hrtimer_get_remaining
|
|
hrtimer_get_res
|
|
hrtimer_init_sleeper
|
|
|
|
|
|
The set_ftrace_notrace prevents those functions from being
|
|
traced.
|
|
|
|
# echo '*preempt*' '*lock*' > set_ftrace_notrace
|
|
|
|
Produces:
|
|
|
|
# tracer: function
|
|
#
|
|
# entries-in-buffer/entries-written: 39608/39608 #P:4
|
|
#
|
|
# _-----=> irqs-off
|
|
# / _----=> need-resched
|
|
# | / _---=> hardirq/softirq
|
|
# || / _--=> preempt-depth
|
|
# ||| / delay
|
|
# TASK-PID CPU# |||| TIMESTAMP FUNCTION
|
|
# | | | |||| | |
|
|
bash-1994 [000] .... 4342.324896: file_ra_state_init <-do_dentry_open
|
|
bash-1994 [000] .... 4342.324897: open_check_o_direct <-do_last
|
|
bash-1994 [000] .... 4342.324897: ima_file_check <-do_last
|
|
bash-1994 [000] .... 4342.324898: process_measurement <-ima_file_check
|
|
bash-1994 [000] .... 4342.324898: ima_get_action <-process_measurement
|
|
bash-1994 [000] .... 4342.324898: ima_match_policy <-ima_get_action
|
|
bash-1994 [000] .... 4342.324899: do_truncate <-do_last
|
|
bash-1994 [000] .... 4342.324899: should_remove_suid <-do_truncate
|
|
bash-1994 [000] .... 4342.324899: notify_change <-do_truncate
|
|
bash-1994 [000] .... 4342.324900: current_fs_time <-notify_change
|
|
bash-1994 [000] .... 4342.324900: current_kernel_time <-current_fs_time
|
|
bash-1994 [000] .... 4342.324900: timespec_trunc <-current_fs_time
|
|
|
|
We can see that there's no more lock or preempt tracing.
|
|
|
|
|
|
Dynamic ftrace with the function graph tracer
|
|
---------------------------------------------
|
|
|
|
Although what has been explained above concerns both the
|
|
function tracer and the function-graph-tracer, there are some
|
|
special features only available in the function-graph tracer.
|
|
|
|
If you want to trace only one function and all of its children,
|
|
you just have to echo its name into set_graph_function:
|
|
|
|
echo __do_fault > set_graph_function
|
|
|
|
will produce the following "expanded" trace of the __do_fault()
|
|
function:
|
|
|
|
0) | __do_fault() {
|
|
0) | filemap_fault() {
|
|
0) | find_lock_page() {
|
|
0) 0.804 us | find_get_page();
|
|
0) | __might_sleep() {
|
|
0) 1.329 us | }
|
|
0) 3.904 us | }
|
|
0) 4.979 us | }
|
|
0) 0.653 us | _spin_lock();
|
|
0) 0.578 us | page_add_file_rmap();
|
|
0) 0.525 us | native_set_pte_at();
|
|
0) 0.585 us | _spin_unlock();
|
|
0) | unlock_page() {
|
|
0) 0.541 us | page_waitqueue();
|
|
0) 0.639 us | __wake_up_bit();
|
|
0) 2.786 us | }
|
|
0) + 14.237 us | }
|
|
0) | __do_fault() {
|
|
0) | filemap_fault() {
|
|
0) | find_lock_page() {
|
|
0) 0.698 us | find_get_page();
|
|
0) | __might_sleep() {
|
|
0) 1.412 us | }
|
|
0) 3.950 us | }
|
|
0) 5.098 us | }
|
|
0) 0.631 us | _spin_lock();
|
|
0) 0.571 us | page_add_file_rmap();
|
|
0) 0.526 us | native_set_pte_at();
|
|
0) 0.586 us | _spin_unlock();
|
|
0) | unlock_page() {
|
|
0) 0.533 us | page_waitqueue();
|
|
0) 0.638 us | __wake_up_bit();
|
|
0) 2.793 us | }
|
|
0) + 14.012 us | }
|
|
|
|
You can also expand several functions at once:
|
|
|
|
echo sys_open > set_graph_function
|
|
echo sys_close >> set_graph_function
|
|
|
|
Now if you want to go back to trace all functions you can clear
|
|
this special filter via:
|
|
|
|
echo > set_graph_function
|
|
|
|
|
|
ftrace_enabled
|
|
--------------
|
|
|
|
Note, the proc sysctl ftrace_enable is a big on/off switch for the
|
|
function tracer. By default it is enabled (when function tracing is
|
|
enabled in the kernel). If it is disabled, all function tracing is
|
|
disabled. This includes not only the function tracers for ftrace, but
|
|
also for any other uses (perf, kprobes, stack tracing, profiling, etc).
|
|
|
|
Please disable this with care.
|
|
|
|
This can be disable (and enabled) with:
|
|
|
|
sysctl kernel.ftrace_enabled=0
|
|
sysctl kernel.ftrace_enabled=1
|
|
|
|
or
|
|
|
|
echo 0 > /proc/sys/kernel/ftrace_enabled
|
|
echo 1 > /proc/sys/kernel/ftrace_enabled
|
|
|
|
|
|
Filter commands
|
|
---------------
|
|
|
|
A few commands are supported by the set_ftrace_filter interface.
|
|
Trace commands have the following format:
|
|
|
|
<function>:<command>:<parameter>
|
|
|
|
The following commands are supported:
|
|
|
|
- mod
|
|
This command enables function filtering per module. The
|
|
parameter defines the module. For example, if only the write*
|
|
functions in the ext3 module are desired, run:
|
|
|
|
echo 'write*:mod:ext3' > set_ftrace_filter
|
|
|
|
This command interacts with the filter in the same way as
|
|
filtering based on function names. Thus, adding more functions
|
|
in a different module is accomplished by appending (>>) to the
|
|
filter file. Remove specific module functions by prepending
|
|
'!':
|
|
|
|
echo '!writeback*:mod:ext3' >> set_ftrace_filter
|
|
|
|
- traceon/traceoff
|
|
These commands turn tracing on and off when the specified
|
|
functions are hit. The parameter determines how many times the
|
|
tracing system is turned on and off. If unspecified, there is
|
|
no limit. For example, to disable tracing when a schedule bug
|
|
is hit the first 5 times, run:
|
|
|
|
echo '__schedule_bug:traceoff:5' > set_ftrace_filter
|
|
|
|
To always disable tracing when __schedule_bug is hit:
|
|
|
|
echo '__schedule_bug:traceoff' > set_ftrace_filter
|
|
|
|
These commands are cumulative whether or not they are appended
|
|
to set_ftrace_filter. To remove a command, prepend it by '!'
|
|
and drop the parameter:
|
|
|
|
echo '!__schedule_bug:traceoff:0' > set_ftrace_filter
|
|
|
|
The above removes the traceoff command for __schedule_bug
|
|
that have a counter. To remove commands without counters:
|
|
|
|
echo '!__schedule_bug:traceoff' > set_ftrace_filter
|
|
|
|
- snapshot
|
|
Will cause a snapshot to be triggered when the function is hit.
|
|
|
|
echo 'native_flush_tlb_others:snapshot' > set_ftrace_filter
|
|
|
|
To only snapshot once:
|
|
|
|
echo 'native_flush_tlb_others:snapshot:1' > set_ftrace_filter
|
|
|
|
To remove the above commands:
|
|
|
|
echo '!native_flush_tlb_others:snapshot' > set_ftrace_filter
|
|
echo '!native_flush_tlb_others:snapshot:0' > set_ftrace_filter
|
|
|
|
- enable_event/disable_event
|
|
These commands can enable or disable a trace event. Note, because
|
|
function tracing callbacks are very sensitive, when these commands
|
|
are registered, the trace point is activated, but disabled in
|
|
a "soft" mode. That is, the tracepoint will be called, but
|
|
just will not be traced. The event tracepoint stays in this mode
|
|
as long as there's a command that triggers it.
|
|
|
|
echo 'try_to_wake_up:enable_event:sched:sched_switch:2' > \
|
|
set_ftrace_filter
|
|
|
|
The format is:
|
|
|
|
<function>:enable_event:<system>:<event>[:count]
|
|
<function>:disable_event:<system>:<event>[:count]
|
|
|
|
To remove the events commands:
|
|
|
|
|
|
echo '!try_to_wake_up:enable_event:sched:sched_switch:0' > \
|
|
set_ftrace_filter
|
|
echo '!schedule:disable_event:sched:sched_switch' > \
|
|
set_ftrace_filter
|
|
|
|
- dump
|
|
When the function is hit, it will dump the contents of the ftrace
|
|
ring buffer to the console. This is useful if you need to debug
|
|
something, and want to dump the trace when a certain function
|
|
is hit. Perhaps its a function that is called before a tripple
|
|
fault happens and does not allow you to get a regular dump.
|
|
|
|
- cpudump
|
|
When the function is hit, it will dump the contents of the ftrace
|
|
ring buffer for the current CPU to the console. Unlike the "dump"
|
|
command, it only prints out the contents of the ring buffer for the
|
|
CPU that executed the function that triggered the dump.
|
|
|
|
trace_pipe
|
|
----------
|
|
|
|
The trace_pipe outputs the same content as the trace file, but
|
|
the effect on the tracing is different. Every read from
|
|
trace_pipe is consumed. This means that subsequent reads will be
|
|
different. The trace is live.
|
|
|
|
# echo function > current_tracer
|
|
# cat trace_pipe > /tmp/trace.out &
|
|
[1] 4153
|
|
# echo 1 > tracing_on
|
|
# usleep 1
|
|
# echo 0 > tracing_on
|
|
# cat trace
|
|
# tracer: function
|
|
#
|
|
# entries-in-buffer/entries-written: 0/0 #P:4
|
|
#
|
|
# _-----=> irqs-off
|
|
# / _----=> need-resched
|
|
# | / _---=> hardirq/softirq
|
|
# || / _--=> preempt-depth
|
|
# ||| / delay
|
|
# TASK-PID CPU# |||| TIMESTAMP FUNCTION
|
|
# | | | |||| | |
|
|
|
|
#
|
|
# cat /tmp/trace.out
|
|
bash-1994 [000] .... 5281.568961: mutex_unlock <-rb_simple_write
|
|
bash-1994 [000] .... 5281.568963: __mutex_unlock_slowpath <-mutex_unlock
|
|
bash-1994 [000] .... 5281.568963: __fsnotify_parent <-fsnotify_modify
|
|
bash-1994 [000] .... 5281.568964: fsnotify <-fsnotify_modify
|
|
bash-1994 [000] .... 5281.568964: __srcu_read_lock <-fsnotify
|
|
bash-1994 [000] .... 5281.568964: add_preempt_count <-__srcu_read_lock
|
|
bash-1994 [000] ...1 5281.568965: sub_preempt_count <-__srcu_read_lock
|
|
bash-1994 [000] .... 5281.568965: __srcu_read_unlock <-fsnotify
|
|
bash-1994 [000] .... 5281.568967: sys_dup2 <-system_call_fastpath
|
|
|
|
|
|
Note, reading the trace_pipe file will block until more input is
|
|
added.
|
|
|
|
trace entries
|
|
-------------
|
|
|
|
Having too much or not enough data can be troublesome in
|
|
diagnosing an issue in the kernel. The file buffer_size_kb is
|
|
used to modify the size of the internal trace buffers. The
|
|
number listed is the number of entries that can be recorded per
|
|
CPU. To know the full size, multiply the number of possible CPUs
|
|
with the number of entries.
|
|
|
|
# cat buffer_size_kb
|
|
1408 (units kilobytes)
|
|
|
|
Or simply read buffer_total_size_kb
|
|
|
|
# cat buffer_total_size_kb
|
|
5632
|
|
|
|
To modify the buffer, simple echo in a number (in 1024 byte segments).
|
|
|
|
# echo 10000 > buffer_size_kb
|
|
# cat buffer_size_kb
|
|
10000 (units kilobytes)
|
|
|
|
It will try to allocate as much as possible. If you allocate too
|
|
much, it can cause Out-Of-Memory to trigger.
|
|
|
|
# echo 1000000000000 > buffer_size_kb
|
|
-bash: echo: write error: Cannot allocate memory
|
|
# cat buffer_size_kb
|
|
85
|
|
|
|
The per_cpu buffers can be changed individually as well:
|
|
|
|
# echo 10000 > per_cpu/cpu0/buffer_size_kb
|
|
# echo 100 > per_cpu/cpu1/buffer_size_kb
|
|
|
|
When the per_cpu buffers are not the same, the buffer_size_kb
|
|
at the top level will just show an X
|
|
|
|
# cat buffer_size_kb
|
|
X
|
|
|
|
This is where the buffer_total_size_kb is useful:
|
|
|
|
# cat buffer_total_size_kb
|
|
12916
|
|
|
|
Writing to the top level buffer_size_kb will reset all the buffers
|
|
to be the same again.
|
|
|
|
Snapshot
|
|
--------
|
|
CONFIG_TRACER_SNAPSHOT makes a generic snapshot feature
|
|
available to all non latency tracers. (Latency tracers which
|
|
record max latency, such as "irqsoff" or "wakeup", can't use
|
|
this feature, since those are already using the snapshot
|
|
mechanism internally.)
|
|
|
|
Snapshot preserves a current trace buffer at a particular point
|
|
in time without stopping tracing. Ftrace swaps the current
|
|
buffer with a spare buffer, and tracing continues in the new
|
|
current (=previous spare) buffer.
|
|
|
|
The following debugfs files in "tracing" are related to this
|
|
feature:
|
|
|
|
snapshot:
|
|
|
|
This is used to take a snapshot and to read the output
|
|
of the snapshot. Echo 1 into this file to allocate a
|
|
spare buffer and to take a snapshot (swap), then read
|
|
the snapshot from this file in the same format as
|
|
"trace" (described above in the section "The File
|
|
System"). Both reads snapshot and tracing are executable
|
|
in parallel. When the spare buffer is allocated, echoing
|
|
0 frees it, and echoing else (positive) values clear the
|
|
snapshot contents.
|
|
More details are shown in the table below.
|
|
|
|
status\input | 0 | 1 | else |
|
|
--------------+------------+------------+------------+
|
|
not allocated |(do nothing)| alloc+swap |(do nothing)|
|
|
--------------+------------+------------+------------+
|
|
allocated | free | swap | clear |
|
|
--------------+------------+------------+------------+
|
|
|
|
Here is an example of using the snapshot feature.
|
|
|
|
# echo 1 > events/sched/enable
|
|
# echo 1 > snapshot
|
|
# cat snapshot
|
|
# tracer: nop
|
|
#
|
|
# entries-in-buffer/entries-written: 71/71 #P:8
|
|
#
|
|
# _-----=> irqs-off
|
|
# / _----=> need-resched
|
|
# | / _---=> hardirq/softirq
|
|
# || / _--=> preempt-depth
|
|
# ||| / delay
|
|
# TASK-PID CPU# |||| TIMESTAMP FUNCTION
|
|
# | | | |||| | |
|
|
<idle>-0 [005] d... 2440.603828: sched_switch: prev_comm=swapper/5 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=snapshot-test-2 next_pid=2242 next_prio=120
|
|
sleep-2242 [005] d... 2440.603846: sched_switch: prev_comm=snapshot-test-2 prev_pid=2242 prev_prio=120 prev_state=R ==> next_comm=kworker/5:1 next_pid=60 next_prio=120
|
|
[...]
|
|
<idle>-0 [002] d... 2440.707230: sched_switch: prev_comm=swapper/2 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=snapshot-test-2 next_pid=2229 next_prio=120
|
|
|
|
# cat trace
|
|
# tracer: nop
|
|
#
|
|
# entries-in-buffer/entries-written: 77/77 #P:8
|
|
#
|
|
# _-----=> irqs-off
|
|
# / _----=> need-resched
|
|
# | / _---=> hardirq/softirq
|
|
# || / _--=> preempt-depth
|
|
# ||| / delay
|
|
# TASK-PID CPU# |||| TIMESTAMP FUNCTION
|
|
# | | | |||| | |
|
|
<idle>-0 [007] d... 2440.707395: sched_switch: prev_comm=swapper/7 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=snapshot-test-2 next_pid=2243 next_prio=120
|
|
snapshot-test-2-2229 [002] d... 2440.707438: sched_switch: prev_comm=snapshot-test-2 prev_pid=2229 prev_prio=120 prev_state=S ==> next_comm=swapper/2 next_pid=0 next_prio=120
|
|
[...]
|
|
|
|
|
|
If you try to use this snapshot feature when current tracer is
|
|
one of the latency tracers, you will get the following results.
|
|
|
|
# echo wakeup > current_tracer
|
|
# echo 1 > snapshot
|
|
bash: echo: write error: Device or resource busy
|
|
# cat snapshot
|
|
cat: snapshot: Device or resource busy
|
|
|
|
|
|
Instances
|
|
---------
|
|
In the debugfs tracing directory is a directory called "instances".
|
|
This directory can have new directories created inside of it using
|
|
mkdir, and removing directories with rmdir. The directory created
|
|
with mkdir in this directory will already contain files and other
|
|
directories after it is created.
|
|
|
|
# mkdir instances/foo
|
|
# ls instances/foo
|
|
buffer_size_kb buffer_total_size_kb events free_buffer per_cpu
|
|
set_event snapshot trace trace_clock trace_marker trace_options
|
|
trace_pipe tracing_on
|
|
|
|
As you can see, the new directory looks similar to the tracing directory
|
|
itself. In fact, it is very similar, except that the buffer and
|
|
events are agnostic from the main director, or from any other
|
|
instances that are created.
|
|
|
|
The files in the new directory work just like the files with the
|
|
same name in the tracing directory except the buffer that is used
|
|
is a separate and new buffer. The files affect that buffer but do not
|
|
affect the main buffer with the exception of trace_options. Currently,
|
|
the trace_options affect all instances and the top level buffer
|
|
the same, but this may change in future releases. That is, options
|
|
may become specific to the instance they reside in.
|
|
|
|
Notice that none of the function tracer files are there, nor is
|
|
current_tracer and available_tracers. This is because the buffers
|
|
can currently only have events enabled for them.
|
|
|
|
# mkdir instances/foo
|
|
# mkdir instances/bar
|
|
# mkdir instances/zoot
|
|
# echo 100000 > buffer_size_kb
|
|
# echo 1000 > instances/foo/buffer_size_kb
|
|
# echo 5000 > instances/bar/per_cpu/cpu1/buffer_size_kb
|
|
# echo function > current_trace
|
|
# echo 1 > instances/foo/events/sched/sched_wakeup/enable
|
|
# echo 1 > instances/foo/events/sched/sched_wakeup_new/enable
|
|
# echo 1 > instances/foo/events/sched/sched_switch/enable
|
|
# echo 1 > instances/bar/events/irq/enable
|
|
# echo 1 > instances/zoot/events/syscalls/enable
|
|
# cat trace_pipe
|
|
CPU:2 [LOST 11745 EVENTS]
|
|
bash-2044 [002] .... 10594.481032: _raw_spin_lock_irqsave <-get_page_from_freelist
|
|
bash-2044 [002] d... 10594.481032: add_preempt_count <-_raw_spin_lock_irqsave
|
|
bash-2044 [002] d..1 10594.481032: __rmqueue <-get_page_from_freelist
|
|
bash-2044 [002] d..1 10594.481033: _raw_spin_unlock <-get_page_from_freelist
|
|
bash-2044 [002] d..1 10594.481033: sub_preempt_count <-_raw_spin_unlock
|
|
bash-2044 [002] d... 10594.481033: get_pageblock_flags_group <-get_pageblock_migratetype
|
|
bash-2044 [002] d... 10594.481034: __mod_zone_page_state <-get_page_from_freelist
|
|
bash-2044 [002] d... 10594.481034: zone_statistics <-get_page_from_freelist
|
|
bash-2044 [002] d... 10594.481034: __inc_zone_state <-zone_statistics
|
|
bash-2044 [002] d... 10594.481034: __inc_zone_state <-zone_statistics
|
|
bash-2044 [002] .... 10594.481035: arch_dup_task_struct <-copy_process
|
|
[...]
|
|
|
|
# cat instances/foo/trace_pipe
|
|
bash-1998 [000] d..4 136.676759: sched_wakeup: comm=kworker/0:1 pid=59 prio=120 success=1 target_cpu=000
|
|
bash-1998 [000] dN.4 136.676760: sched_wakeup: comm=bash pid=1998 prio=120 success=1 target_cpu=000
|
|
<idle>-0 [003] d.h3 136.676906: sched_wakeup: comm=rcu_preempt pid=9 prio=120 success=1 target_cpu=003
|
|
<idle>-0 [003] d..3 136.676909: sched_switch: prev_comm=swapper/3 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=rcu_preempt next_pid=9 next_prio=120
|
|
rcu_preempt-9 [003] d..3 136.676916: sched_switch: prev_comm=rcu_preempt prev_pid=9 prev_prio=120 prev_state=S ==> next_comm=swapper/3 next_pid=0 next_prio=120
|
|
bash-1998 [000] d..4 136.677014: sched_wakeup: comm=kworker/0:1 pid=59 prio=120 success=1 target_cpu=000
|
|
bash-1998 [000] dN.4 136.677016: sched_wakeup: comm=bash pid=1998 prio=120 success=1 target_cpu=000
|
|
bash-1998 [000] d..3 136.677018: sched_switch: prev_comm=bash prev_pid=1998 prev_prio=120 prev_state=R+ ==> next_comm=kworker/0:1 next_pid=59 next_prio=120
|
|
kworker/0:1-59 [000] d..4 136.677022: sched_wakeup: comm=sshd pid=1995 prio=120 success=1 target_cpu=001
|
|
kworker/0:1-59 [000] d..3 136.677025: sched_switch: prev_comm=kworker/0:1 prev_pid=59 prev_prio=120 prev_state=S ==> next_comm=bash next_pid=1998 next_prio=120
|
|
[...]
|
|
|
|
# cat instances/bar/trace_pipe
|
|
migration/1-14 [001] d.h3 138.732674: softirq_raise: vec=3 [action=NET_RX]
|
|
<idle>-0 [001] dNh3 138.732725: softirq_raise: vec=3 [action=NET_RX]
|
|
bash-1998 [000] d.h1 138.733101: softirq_raise: vec=1 [action=TIMER]
|
|
bash-1998 [000] d.h1 138.733102: softirq_raise: vec=9 [action=RCU]
|
|
bash-1998 [000] ..s2 138.733105: softirq_entry: vec=1 [action=TIMER]
|
|
bash-1998 [000] ..s2 138.733106: softirq_exit: vec=1 [action=TIMER]
|
|
bash-1998 [000] ..s2 138.733106: softirq_entry: vec=9 [action=RCU]
|
|
bash-1998 [000] ..s2 138.733109: softirq_exit: vec=9 [action=RCU]
|
|
sshd-1995 [001] d.h1 138.733278: irq_handler_entry: irq=21 name=uhci_hcd:usb4
|
|
sshd-1995 [001] d.h1 138.733280: irq_handler_exit: irq=21 ret=unhandled
|
|
sshd-1995 [001] d.h1 138.733281: irq_handler_entry: irq=21 name=eth0
|
|
sshd-1995 [001] d.h1 138.733283: irq_handler_exit: irq=21 ret=handled
|
|
[...]
|
|
|
|
# cat instances/zoot/trace
|
|
# tracer: nop
|
|
#
|
|
# entries-in-buffer/entries-written: 18996/18996 #P:4
|
|
#
|
|
# _-----=> irqs-off
|
|
# / _----=> need-resched
|
|
# | / _---=> hardirq/softirq
|
|
# || / _--=> preempt-depth
|
|
# ||| / delay
|
|
# TASK-PID CPU# |||| TIMESTAMP FUNCTION
|
|
# | | | |||| | |
|
|
bash-1998 [000] d... 140.733501: sys_write -> 0x2
|
|
bash-1998 [000] d... 140.733504: sys_dup2(oldfd: a, newfd: 1)
|
|
bash-1998 [000] d... 140.733506: sys_dup2 -> 0x1
|
|
bash-1998 [000] d... 140.733508: sys_fcntl(fd: a, cmd: 1, arg: 0)
|
|
bash-1998 [000] d... 140.733509: sys_fcntl -> 0x1
|
|
bash-1998 [000] d... 140.733510: sys_close(fd: a)
|
|
bash-1998 [000] d... 140.733510: sys_close -> 0x0
|
|
bash-1998 [000] d... 140.733514: sys_rt_sigprocmask(how: 0, nset: 0, oset: 6e2768, sigsetsize: 8)
|
|
bash-1998 [000] d... 140.733515: sys_rt_sigprocmask -> 0x0
|
|
bash-1998 [000] d... 140.733516: sys_rt_sigaction(sig: 2, act: 7fff718846f0, oact: 7fff71884650, sigsetsize: 8)
|
|
bash-1998 [000] d... 140.733516: sys_rt_sigaction -> 0x0
|
|
|
|
You can see that the trace of the top most trace buffer shows only
|
|
the function tracing. The foo instance displays wakeups and task
|
|
switches.
|
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|
|
To remove the instances, simply delete their directories:
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|
|
|
# rmdir instances/foo
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|
# rmdir instances/bar
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|
# rmdir instances/zoot
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|
|
|
Note, if a process has a trace file open in one of the instance
|
|
directories, the rmdir will fail with EBUSY.
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|
|
|
|
|
Stack trace
|
|
-----------
|
|
Since the kernel has a fixed sized stack, it is important not to
|
|
waste it in functions. A kernel developer must be conscience of
|
|
what they allocate on the stack. If they add too much, the system
|
|
can be in danger of a stack overflow, and corruption will occur,
|
|
usually leading to a system panic.
|
|
|
|
There are some tools that check this, usually with interrupts
|
|
periodically checking usage. But if you can perform a check
|
|
at every function call that will become very useful. As ftrace provides
|
|
a function tracer, it makes it convenient to check the stack size
|
|
at every function call. This is enabled via the stack tracer.
|
|
|
|
CONFIG_STACK_TRACER enables the ftrace stack tracing functionality.
|
|
To enable it, write a '1' into /proc/sys/kernel/stack_tracer_enabled.
|
|
|
|
# echo 1 > /proc/sys/kernel/stack_tracer_enabled
|
|
|
|
You can also enable it from the kernel command line to trace
|
|
the stack size of the kernel during boot up, by adding "stacktrace"
|
|
to the kernel command line parameter.
|
|
|
|
After running it for a few minutes, the output looks like:
|
|
|
|
# cat stack_max_size
|
|
2928
|
|
|
|
# cat stack_trace
|
|
Depth Size Location (18 entries)
|
|
----- ---- --------
|
|
0) 2928 224 update_sd_lb_stats+0xbc/0x4ac
|
|
1) 2704 160 find_busiest_group+0x31/0x1f1
|
|
2) 2544 256 load_balance+0xd9/0x662
|
|
3) 2288 80 idle_balance+0xbb/0x130
|
|
4) 2208 128 __schedule+0x26e/0x5b9
|
|
5) 2080 16 schedule+0x64/0x66
|
|
6) 2064 128 schedule_timeout+0x34/0xe0
|
|
7) 1936 112 wait_for_common+0x97/0xf1
|
|
8) 1824 16 wait_for_completion+0x1d/0x1f
|
|
9) 1808 128 flush_work+0xfe/0x119
|
|
10) 1680 16 tty_flush_to_ldisc+0x1e/0x20
|
|
11) 1664 48 input_available_p+0x1d/0x5c
|
|
12) 1616 48 n_tty_poll+0x6d/0x134
|
|
13) 1568 64 tty_poll+0x64/0x7f
|
|
14) 1504 880 do_select+0x31e/0x511
|
|
15) 624 400 core_sys_select+0x177/0x216
|
|
16) 224 96 sys_select+0x91/0xb9
|
|
17) 128 128 system_call_fastpath+0x16/0x1b
|
|
|
|
Note, if -mfentry is being used by gcc, functions get traced before
|
|
they set up the stack frame. This means that leaf level functions
|
|
are not tested by the stack tracer when -mfentry is used.
|
|
|
|
Currently, -mfentry is used by gcc 4.6.0 and above on x86 only.
|
|
|
|
---------
|
|
|
|
More details can be found in the source code, in the
|
|
kernel/trace/*.c files.
|