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Current implementation of cpuset track N_HIGH_MEMORY instead N_MEMORY. (N_MEMORY doesn't exist in current implementation) Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Acked-by: Paul Jackson <pj@sgi.com> Cc: Christoph Lameter <clameter@sgi.com> Cc: Paul Menage <menage@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
729 lines
31 KiB
Plaintext
729 lines
31 KiB
Plaintext
CPUSETS
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-------
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Copyright (C) 2004 BULL SA.
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Written by Simon.Derr@bull.net
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Portions Copyright (c) 2004-2006 Silicon Graphics, Inc.
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Modified by Paul Jackson <pj@sgi.com>
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Modified by Christoph Lameter <clameter@sgi.com>
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Modified by Paul Menage <menage@google.com>
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CONTENTS:
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=========
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1. Cpusets
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1.1 What are cpusets ?
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1.2 Why are cpusets needed ?
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1.3 How are cpusets implemented ?
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1.4 What are exclusive cpusets ?
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1.5 What is memory_pressure ?
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1.6 What is memory spread ?
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1.7 What is sched_load_balance ?
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1.8 How do I use cpusets ?
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2. Usage Examples and Syntax
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2.1 Basic Usage
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2.2 Adding/removing cpus
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2.3 Setting flags
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2.4 Attaching processes
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3. Questions
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4. Contact
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1. Cpusets
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==========
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1.1 What are cpusets ?
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----------------------
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Cpusets provide a mechanism for assigning a set of CPUs and Memory
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Nodes to a set of tasks. In this document "Memory Node" refers to
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an on-line node that contains memory.
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Cpusets constrain the CPU and Memory placement of tasks to only
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the resources within a tasks current cpuset. They form a nested
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hierarchy visible in a virtual file system. These are the essential
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hooks, beyond what is already present, required to manage dynamic
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job placement on large systems.
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Cpusets use the generic cgroup subsystem described in
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Documentation/cgroup.txt.
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Requests by a task, using the sched_setaffinity(2) system call to
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include CPUs in its CPU affinity mask, and using the mbind(2) and
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set_mempolicy(2) system calls to include Memory Nodes in its memory
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policy, are both filtered through that tasks cpuset, filtering out any
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CPUs or Memory Nodes not in that cpuset. The scheduler will not
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schedule a task on a CPU that is not allowed in its cpus_allowed
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vector, and the kernel page allocator will not allocate a page on a
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node that is not allowed in the requesting tasks mems_allowed vector.
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User level code may create and destroy cpusets by name in the cgroup
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virtual file system, manage the attributes and permissions of these
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cpusets and which CPUs and Memory Nodes are assigned to each cpuset,
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specify and query to which cpuset a task is assigned, and list the
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task pids assigned to a cpuset.
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1.2 Why are cpusets needed ?
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----------------------------
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The management of large computer systems, with many processors (CPUs),
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complex memory cache hierarchies and multiple Memory Nodes having
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non-uniform access times (NUMA) presents additional challenges for
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the efficient scheduling and memory placement of processes.
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Frequently more modest sized systems can be operated with adequate
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efficiency just by letting the operating system automatically share
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the available CPU and Memory resources amongst the requesting tasks.
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But larger systems, which benefit more from careful processor and
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memory placement to reduce memory access times and contention,
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and which typically represent a larger investment for the customer,
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can benefit from explicitly placing jobs on properly sized subsets of
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the system.
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This can be especially valuable on:
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* Web Servers running multiple instances of the same web application,
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* Servers running different applications (for instance, a web server
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and a database), or
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* NUMA systems running large HPC applications with demanding
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performance characteristics.
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These subsets, or "soft partitions" must be able to be dynamically
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adjusted, as the job mix changes, without impacting other concurrently
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executing jobs. The location of the running jobs pages may also be moved
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when the memory locations are changed.
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The kernel cpuset patch provides the minimum essential kernel
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mechanisms required to efficiently implement such subsets. It
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leverages existing CPU and Memory Placement facilities in the Linux
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kernel to avoid any additional impact on the critical scheduler or
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memory allocator code.
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1.3 How are cpusets implemented ?
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---------------------------------
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Cpusets provide a Linux kernel mechanism to constrain which CPUs and
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Memory Nodes are used by a process or set of processes.
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The Linux kernel already has a pair of mechanisms to specify on which
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CPUs a task may be scheduled (sched_setaffinity) and on which Memory
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Nodes it may obtain memory (mbind, set_mempolicy).
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Cpusets extends these two mechanisms as follows:
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- Cpusets are sets of allowed CPUs and Memory Nodes, known to the
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kernel.
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- Each task in the system is attached to a cpuset, via a pointer
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in the task structure to a reference counted cgroup structure.
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- Calls to sched_setaffinity are filtered to just those CPUs
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allowed in that tasks cpuset.
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- Calls to mbind and set_mempolicy are filtered to just
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those Memory Nodes allowed in that tasks cpuset.
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- The root cpuset contains all the systems CPUs and Memory
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Nodes.
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- For any cpuset, one can define child cpusets containing a subset
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of the parents CPU and Memory Node resources.
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- The hierarchy of cpusets can be mounted at /dev/cpuset, for
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browsing and manipulation from user space.
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- A cpuset may be marked exclusive, which ensures that no other
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cpuset (except direct ancestors and descendents) may contain
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any overlapping CPUs or Memory Nodes.
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- You can list all the tasks (by pid) attached to any cpuset.
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The implementation of cpusets requires a few, simple hooks
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into the rest of the kernel, none in performance critical paths:
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- in init/main.c, to initialize the root cpuset at system boot.
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- in fork and exit, to attach and detach a task from its cpuset.
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- in sched_setaffinity, to mask the requested CPUs by what's
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allowed in that tasks cpuset.
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- in sched.c migrate_all_tasks(), to keep migrating tasks within
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the CPUs allowed by their cpuset, if possible.
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- in the mbind and set_mempolicy system calls, to mask the requested
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Memory Nodes by what's allowed in that tasks cpuset.
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- in page_alloc.c, to restrict memory to allowed nodes.
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- in vmscan.c, to restrict page recovery to the current cpuset.
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You should mount the "cgroup" filesystem type in order to enable
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browsing and modifying the cpusets presently known to the kernel. No
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new system calls are added for cpusets - all support for querying and
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modifying cpusets is via this cpuset file system.
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The /proc/<pid>/status file for each task has two added lines,
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displaying the tasks cpus_allowed (on which CPUs it may be scheduled)
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and mems_allowed (on which Memory Nodes it may obtain memory),
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in the format seen in the following example:
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Cpus_allowed: ffffffff,ffffffff,ffffffff,ffffffff
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Mems_allowed: ffffffff,ffffffff
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Each cpuset is represented by a directory in the cgroup file system
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containing (on top of the standard cgroup files) the following
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files describing that cpuset:
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- cpus: list of CPUs in that cpuset
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- mems: list of Memory Nodes in that cpuset
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- memory_migrate flag: if set, move pages to cpusets nodes
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- cpu_exclusive flag: is cpu placement exclusive?
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- mem_exclusive flag: is memory placement exclusive?
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- memory_pressure: measure of how much paging pressure in cpuset
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In addition, the root cpuset only has the following file:
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- memory_pressure_enabled flag: compute memory_pressure?
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New cpusets are created using the mkdir system call or shell
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command. The properties of a cpuset, such as its flags, allowed
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CPUs and Memory Nodes, and attached tasks, are modified by writing
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to the appropriate file in that cpusets directory, as listed above.
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The named hierarchical structure of nested cpusets allows partitioning
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a large system into nested, dynamically changeable, "soft-partitions".
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The attachment of each task, automatically inherited at fork by any
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children of that task, to a cpuset allows organizing the work load
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on a system into related sets of tasks such that each set is constrained
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to using the CPUs and Memory Nodes of a particular cpuset. A task
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may be re-attached to any other cpuset, if allowed by the permissions
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on the necessary cpuset file system directories.
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Such management of a system "in the large" integrates smoothly with
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the detailed placement done on individual tasks and memory regions
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using the sched_setaffinity, mbind and set_mempolicy system calls.
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The following rules apply to each cpuset:
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- Its CPUs and Memory Nodes must be a subset of its parents.
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- It can only be marked exclusive if its parent is.
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- If its cpu or memory is exclusive, they may not overlap any sibling.
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These rules, and the natural hierarchy of cpusets, enable efficient
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enforcement of the exclusive guarantee, without having to scan all
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cpusets every time any of them change to ensure nothing overlaps a
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exclusive cpuset. Also, the use of a Linux virtual file system (vfs)
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to represent the cpuset hierarchy provides for a familiar permission
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and name space for cpusets, with a minimum of additional kernel code.
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The cpus and mems files in the root (top_cpuset) cpuset are
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read-only. The cpus file automatically tracks the value of
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cpu_online_map using a CPU hotplug notifier, and the mems file
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automatically tracks the value of node_states[N_HIGH_MEMORY]--i.e.,
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nodes with memory--using the cpuset_track_online_nodes() hook.
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1.4 What are exclusive cpusets ?
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--------------------------------
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If a cpuset is cpu or mem exclusive, no other cpuset, other than
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a direct ancestor or descendent, may share any of the same CPUs or
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Memory Nodes.
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A cpuset that is mem_exclusive restricts kernel allocations for
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page, buffer and other data commonly shared by the kernel across
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multiple users. All cpusets, whether mem_exclusive or not, restrict
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allocations of memory for user space. This enables configuring a
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system so that several independent jobs can share common kernel data,
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such as file system pages, while isolating each jobs user allocation in
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its own cpuset. To do this, construct a large mem_exclusive cpuset to
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hold all the jobs, and construct child, non-mem_exclusive cpusets for
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each individual job. Only a small amount of typical kernel memory,
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such as requests from interrupt handlers, is allowed to be taken
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outside even a mem_exclusive cpuset.
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1.5 What is memory_pressure ?
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-----------------------------
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The memory_pressure of a cpuset provides a simple per-cpuset metric
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of the rate that the tasks in a cpuset are attempting to free up in
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use memory on the nodes of the cpuset to satisfy additional memory
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requests.
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This enables batch managers monitoring jobs running in dedicated
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cpusets to efficiently detect what level of memory pressure that job
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is causing.
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This is useful both on tightly managed systems running a wide mix of
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submitted jobs, which may choose to terminate or re-prioritize jobs that
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are trying to use more memory than allowed on the nodes assigned them,
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and with tightly coupled, long running, massively parallel scientific
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computing jobs that will dramatically fail to meet required performance
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goals if they start to use more memory than allowed to them.
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This mechanism provides a very economical way for the batch manager
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to monitor a cpuset for signs of memory pressure. It's up to the
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batch manager or other user code to decide what to do about it and
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take action.
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==> Unless this feature is enabled by writing "1" to the special file
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/dev/cpuset/memory_pressure_enabled, the hook in the rebalance
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code of __alloc_pages() for this metric reduces to simply noticing
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that the cpuset_memory_pressure_enabled flag is zero. So only
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systems that enable this feature will compute the metric.
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Why a per-cpuset, running average:
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Because this meter is per-cpuset, rather than per-task or mm,
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the system load imposed by a batch scheduler monitoring this
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metric is sharply reduced on large systems, because a scan of
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the tasklist can be avoided on each set of queries.
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Because this meter is a running average, instead of an accumulating
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counter, a batch scheduler can detect memory pressure with a
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single read, instead of having to read and accumulate results
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for a period of time.
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Because this meter is per-cpuset rather than per-task or mm,
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the batch scheduler can obtain the key information, memory
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pressure in a cpuset, with a single read, rather than having to
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query and accumulate results over all the (dynamically changing)
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set of tasks in the cpuset.
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A per-cpuset simple digital filter (requires a spinlock and 3 words
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of data per-cpuset) is kept, and updated by any task attached to that
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cpuset, if it enters the synchronous (direct) page reclaim code.
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A per-cpuset file provides an integer number representing the recent
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(half-life of 10 seconds) rate of direct page reclaims caused by
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the tasks in the cpuset, in units of reclaims attempted per second,
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times 1000.
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1.6 What is memory spread ?
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---------------------------
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There are two boolean flag files per cpuset that control where the
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kernel allocates pages for the file system buffers and related in
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kernel data structures. They are called 'memory_spread_page' and
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'memory_spread_slab'.
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If the per-cpuset boolean flag file 'memory_spread_page' is set, then
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the kernel will spread the file system buffers (page cache) evenly
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over all the nodes that the faulting task is allowed to use, instead
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of preferring to put those pages on the node where the task is running.
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If the per-cpuset boolean flag file 'memory_spread_slab' is set,
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then the kernel will spread some file system related slab caches,
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such as for inodes and dentries evenly over all the nodes that the
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faulting task is allowed to use, instead of preferring to put those
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pages on the node where the task is running.
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The setting of these flags does not affect anonymous data segment or
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stack segment pages of a task.
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By default, both kinds of memory spreading are off, and memory
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pages are allocated on the node local to where the task is running,
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except perhaps as modified by the tasks NUMA mempolicy or cpuset
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configuration, so long as sufficient free memory pages are available.
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When new cpusets are created, they inherit the memory spread settings
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of their parent.
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Setting memory spreading causes allocations for the affected page
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or slab caches to ignore the tasks NUMA mempolicy and be spread
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instead. Tasks using mbind() or set_mempolicy() calls to set NUMA
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mempolicies will not notice any change in these calls as a result of
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their containing tasks memory spread settings. If memory spreading
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is turned off, then the currently specified NUMA mempolicy once again
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applies to memory page allocations.
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Both 'memory_spread_page' and 'memory_spread_slab' are boolean flag
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files. By default they contain "0", meaning that the feature is off
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for that cpuset. If a "1" is written to that file, then that turns
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the named feature on.
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The implementation is simple.
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Setting the flag 'memory_spread_page' turns on a per-process flag
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PF_SPREAD_PAGE for each task that is in that cpuset or subsequently
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joins that cpuset. The page allocation calls for the page cache
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is modified to perform an inline check for this PF_SPREAD_PAGE task
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flag, and if set, a call to a new routine cpuset_mem_spread_node()
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returns the node to prefer for the allocation.
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Similarly, setting 'memory_spread_cache' turns on the flag
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PF_SPREAD_SLAB, and appropriately marked slab caches will allocate
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pages from the node returned by cpuset_mem_spread_node().
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The cpuset_mem_spread_node() routine is also simple. It uses the
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value of a per-task rotor cpuset_mem_spread_rotor to select the next
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node in the current tasks mems_allowed to prefer for the allocation.
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This memory placement policy is also known (in other contexts) as
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round-robin or interleave.
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This policy can provide substantial improvements for jobs that need
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to place thread local data on the corresponding node, but that need
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to access large file system data sets that need to be spread across
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the several nodes in the jobs cpuset in order to fit. Without this
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policy, especially for jobs that might have one thread reading in the
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data set, the memory allocation across the nodes in the jobs cpuset
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can become very uneven.
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1.7 What is sched_load_balance ?
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--------------------------------
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The kernel scheduler (kernel/sched.c) automatically load balances
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tasks. If one CPU is underutilized, kernel code running on that
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CPU will look for tasks on other more overloaded CPUs and move those
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tasks to itself, within the constraints of such placement mechanisms
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as cpusets and sched_setaffinity.
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The algorithmic cost of load balancing and its impact on key shared
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kernel data structures such as the task list increases more than
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linearly with the number of CPUs being balanced. So the scheduler
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has support to partition the systems CPUs into a number of sched
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domains such that it only load balances within each sched domain.
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Each sched domain covers some subset of the CPUs in the system;
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no two sched domains overlap; some CPUs might not be in any sched
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domain and hence won't be load balanced.
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Put simply, it costs less to balance between two smaller sched domains
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than one big one, but doing so means that overloads in one of the
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two domains won't be load balanced to the other one.
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By default, there is one sched domain covering all CPUs, except those
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marked isolated using the kernel boot time "isolcpus=" argument.
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This default load balancing across all CPUs is not well suited for
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the following two situations:
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1) On large systems, load balancing across many CPUs is expensive.
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If the system is managed using cpusets to place independent jobs
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on separate sets of CPUs, full load balancing is unnecessary.
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2) Systems supporting realtime on some CPUs need to minimize
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system overhead on those CPUs, including avoiding task load
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balancing if that is not needed.
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When the per-cpuset flag "sched_load_balance" is enabled (the default
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setting), it requests that all the CPUs in that cpusets allowed 'cpus'
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be contained in a single sched domain, ensuring that load balancing
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can move a task (not otherwised pinned, as by sched_setaffinity)
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from any CPU in that cpuset to any other.
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When the per-cpuset flag "sched_load_balance" is disabled, then the
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scheduler will avoid load balancing across the CPUs in that cpuset,
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--except-- in so far as is necessary because some overlapping cpuset
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has "sched_load_balance" enabled.
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So, for example, if the top cpuset has the flag "sched_load_balance"
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enabled, then the scheduler will have one sched domain covering all
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CPUs, and the setting of the "sched_load_balance" flag in any other
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cpusets won't matter, as we're already fully load balancing.
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Therefore in the above two situations, the top cpuset flag
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"sched_load_balance" should be disabled, and only some of the smaller,
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child cpusets have this flag enabled.
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When doing this, you don't usually want to leave any unpinned tasks in
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the top cpuset that might use non-trivial amounts of CPU, as such tasks
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may be artificially constrained to some subset of CPUs, depending on
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the particulars of this flag setting in descendent cpusets. Even if
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such a task could use spare CPU cycles in some other CPUs, the kernel
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scheduler might not consider the possibility of load balancing that
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task to that underused CPU.
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Of course, tasks pinned to a particular CPU can be left in a cpuset
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that disables "sched_load_balance" as those tasks aren't going anywhere
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else anyway.
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There is an impedance mismatch here, between cpusets and sched domains.
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Cpusets are hierarchical and nest. Sched domains are flat; they don't
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overlap and each CPU is in at most one sched domain.
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It is necessary for sched domains to be flat because load balancing
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across partially overlapping sets of CPUs would risk unstable dynamics
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that would be beyond our understanding. So if each of two partially
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overlapping cpusets enables the flag 'sched_load_balance', then we
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form a single sched domain that is a superset of both. We won't move
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a task to a CPU outside it cpuset, but the scheduler load balancing
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code might waste some compute cycles considering that possibility.
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This mismatch is why there is not a simple one-to-one relation
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between which cpusets have the flag "sched_load_balance" enabled,
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and the sched domain configuration. If a cpuset enables the flag, it
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will get balancing across all its CPUs, but if it disables the flag,
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it will only be assured of no load balancing if no other overlapping
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cpuset enables the flag.
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If two cpusets have partially overlapping 'cpus' allowed, and only
|
|
one of them has this flag enabled, then the other may find its
|
|
tasks only partially load balanced, just on the overlapping CPUs.
|
|
This is just the general case of the top_cpuset example given a few
|
|
paragraphs above. In the general case, as in the top cpuset case,
|
|
don't leave tasks that might use non-trivial amounts of CPU in
|
|
such partially load balanced cpusets, as they may be artificially
|
|
constrained to some subset of the CPUs allowed to them, for lack of
|
|
load balancing to the other CPUs.
|
|
|
|
1.7.1 sched_load_balance implementation details.
|
|
------------------------------------------------
|
|
|
|
The per-cpuset flag 'sched_load_balance' defaults to enabled (contrary
|
|
to most cpuset flags.) When enabled for a cpuset, the kernel will
|
|
ensure that it can load balance across all the CPUs in that cpuset
|
|
(makes sure that all the CPUs in the cpus_allowed of that cpuset are
|
|
in the same sched domain.)
|
|
|
|
If two overlapping cpusets both have 'sched_load_balance' enabled,
|
|
then they will be (must be) both in the same sched domain.
|
|
|
|
If, as is the default, the top cpuset has 'sched_load_balance' enabled,
|
|
then by the above that means there is a single sched domain covering
|
|
the whole system, regardless of any other cpuset settings.
|
|
|
|
The kernel commits to user space that it will avoid load balancing
|
|
where it can. It will pick as fine a granularity partition of sched
|
|
domains as it can while still providing load balancing for any set
|
|
of CPUs allowed to a cpuset having 'sched_load_balance' enabled.
|
|
|
|
The internal kernel cpuset to scheduler interface passes from the
|
|
cpuset code to the scheduler code a partition of the load balanced
|
|
CPUs in the system. This partition is a set of subsets (represented
|
|
as an array of cpumask_t) of CPUs, pairwise disjoint, that cover all
|
|
the CPUs that must be load balanced.
|
|
|
|
Whenever the 'sched_load_balance' flag changes, or CPUs come or go
|
|
from a cpuset with this flag enabled, or a cpuset with this flag
|
|
enabled is removed, the cpuset code builds a new such partition and
|
|
passes it to the scheduler sched domain setup code, to have the sched
|
|
domains rebuilt as necessary.
|
|
|
|
This partition exactly defines what sched domains the scheduler should
|
|
setup - one sched domain for each element (cpumask_t) in the partition.
|
|
|
|
The scheduler remembers the currently active sched domain partitions.
|
|
When the scheduler routine partition_sched_domains() is invoked from
|
|
the cpuset code to update these sched domains, it compares the new
|
|
partition requested with the current, and updates its sched domains,
|
|
removing the old and adding the new, for each change.
|
|
|
|
1.8 How do I use cpusets ?
|
|
--------------------------
|
|
|
|
In order to minimize the impact of cpusets on critical kernel
|
|
code, such as the scheduler, and due to the fact that the kernel
|
|
does not support one task updating the memory placement of another
|
|
task directly, the impact on a task of changing its cpuset CPU
|
|
or Memory Node placement, or of changing to which cpuset a task
|
|
is attached, is subtle.
|
|
|
|
If a cpuset has its Memory Nodes modified, then for each task attached
|
|
to that cpuset, the next time that the kernel attempts to allocate
|
|
a page of memory for that task, the kernel will notice the change
|
|
in the tasks cpuset, and update its per-task memory placement to
|
|
remain within the new cpusets memory placement. If the task was using
|
|
mempolicy MPOL_BIND, and the nodes to which it was bound overlap with
|
|
its new cpuset, then the task will continue to use whatever subset
|
|
of MPOL_BIND nodes are still allowed in the new cpuset. If the task
|
|
was using MPOL_BIND and now none of its MPOL_BIND nodes are allowed
|
|
in the new cpuset, then the task will be essentially treated as if it
|
|
was MPOL_BIND bound to the new cpuset (even though its numa placement,
|
|
as queried by get_mempolicy(), doesn't change). If a task is moved
|
|
from one cpuset to another, then the kernel will adjust the tasks
|
|
memory placement, as above, the next time that the kernel attempts
|
|
to allocate a page of memory for that task.
|
|
|
|
If a cpuset has its 'cpus' modified, then each task in that cpuset
|
|
will have its allowed CPU placement changed immediately. Similarly,
|
|
if a tasks pid is written to a cpusets 'tasks' file, in either its
|
|
current cpuset or another cpuset, then its allowed CPU placement is
|
|
changed immediately. If such a task had been bound to some subset
|
|
of its cpuset using the sched_setaffinity() call, the task will be
|
|
allowed to run on any CPU allowed in its new cpuset, negating the
|
|
affect of the prior sched_setaffinity() call.
|
|
|
|
In summary, the memory placement of a task whose cpuset is changed is
|
|
updated by the kernel, on the next allocation of a page for that task,
|
|
but the processor placement is not updated, until that tasks pid is
|
|
rewritten to the 'tasks' file of its cpuset. This is done to avoid
|
|
impacting the scheduler code in the kernel with a check for changes
|
|
in a tasks processor placement.
|
|
|
|
Normally, once a page is allocated (given a physical page
|
|
of main memory) then that page stays on whatever node it
|
|
was allocated, so long as it remains allocated, even if the
|
|
cpusets memory placement policy 'mems' subsequently changes.
|
|
If the cpuset flag file 'memory_migrate' is set true, then when
|
|
tasks are attached to that cpuset, any pages that task had
|
|
allocated to it on nodes in its previous cpuset are migrated
|
|
to the tasks new cpuset. The relative placement of the page within
|
|
the cpuset is preserved during these migration operations if possible.
|
|
For example if the page was on the second valid node of the prior cpuset
|
|
then the page will be placed on the second valid node of the new cpuset.
|
|
|
|
Also if 'memory_migrate' is set true, then if that cpusets
|
|
'mems' file is modified, pages allocated to tasks in that
|
|
cpuset, that were on nodes in the previous setting of 'mems',
|
|
will be moved to nodes in the new setting of 'mems.'
|
|
Pages that were not in the tasks prior cpuset, or in the cpusets
|
|
prior 'mems' setting, will not be moved.
|
|
|
|
There is an exception to the above. If hotplug functionality is used
|
|
to remove all the CPUs that are currently assigned to a cpuset,
|
|
then the kernel will automatically update the cpus_allowed of all
|
|
tasks attached to CPUs in that cpuset to allow all CPUs. When memory
|
|
hotplug functionality for removing Memory Nodes is available, a
|
|
similar exception is expected to apply there as well. In general,
|
|
the kernel prefers to violate cpuset placement, over starving a task
|
|
that has had all its allowed CPUs or Memory Nodes taken offline. User
|
|
code should reconfigure cpusets to only refer to online CPUs and Memory
|
|
Nodes when using hotplug to add or remove such resources.
|
|
|
|
There is a second exception to the above. GFP_ATOMIC requests are
|
|
kernel internal allocations that must be satisfied, immediately.
|
|
The kernel may drop some request, in rare cases even panic, if a
|
|
GFP_ATOMIC alloc fails. If the request cannot be satisfied within
|
|
the current tasks cpuset, then we relax the cpuset, and look for
|
|
memory anywhere we can find it. It's better to violate the cpuset
|
|
than stress the kernel.
|
|
|
|
To start a new job that is to be contained within a cpuset, the steps are:
|
|
|
|
1) mkdir /dev/cpuset
|
|
2) mount -t cgroup -ocpuset cpuset /dev/cpuset
|
|
3) Create the new cpuset by doing mkdir's and write's (or echo's) in
|
|
the /dev/cpuset virtual file system.
|
|
4) Start a task that will be the "founding father" of the new job.
|
|
5) Attach that task to the new cpuset by writing its pid to the
|
|
/dev/cpuset tasks file for that cpuset.
|
|
6) fork, exec or clone the job tasks from this founding father task.
|
|
|
|
For example, the following sequence of commands will setup a cpuset
|
|
named "Charlie", containing just CPUs 2 and 3, and Memory Node 1,
|
|
and then start a subshell 'sh' in that cpuset:
|
|
|
|
mount -t cgroup -ocpuset cpuset /dev/cpuset
|
|
cd /dev/cpuset
|
|
mkdir Charlie
|
|
cd Charlie
|
|
/bin/echo 2-3 > cpus
|
|
/bin/echo 1 > mems
|
|
/bin/echo $$ > tasks
|
|
sh
|
|
# The subshell 'sh' is now running in cpuset Charlie
|
|
# The next line should display '/Charlie'
|
|
cat /proc/self/cpuset
|
|
|
|
In the future, a C library interface to cpusets will likely be
|
|
available. For now, the only way to query or modify cpusets is
|
|
via the cpuset file system, using the various cd, mkdir, echo, cat,
|
|
rmdir commands from the shell, or their equivalent from C.
|
|
|
|
The sched_setaffinity calls can also be done at the shell prompt using
|
|
SGI's runon or Robert Love's taskset. The mbind and set_mempolicy
|
|
calls can be done at the shell prompt using the numactl command
|
|
(part of Andi Kleen's numa package).
|
|
|
|
2. Usage Examples and Syntax
|
|
============================
|
|
|
|
2.1 Basic Usage
|
|
---------------
|
|
|
|
Creating, modifying, using the cpusets can be done through the cpuset
|
|
virtual filesystem.
|
|
|
|
To mount it, type:
|
|
# mount -t cgroup -o cpuset cpuset /dev/cpuset
|
|
|
|
Then under /dev/cpuset you can find a tree that corresponds to the
|
|
tree of the cpusets in the system. For instance, /dev/cpuset
|
|
is the cpuset that holds the whole system.
|
|
|
|
If you want to create a new cpuset under /dev/cpuset:
|
|
# cd /dev/cpuset
|
|
# mkdir my_cpuset
|
|
|
|
Now you want to do something with this cpuset.
|
|
# cd my_cpuset
|
|
|
|
In this directory you can find several files:
|
|
# ls
|
|
cpus cpu_exclusive mems mem_exclusive tasks
|
|
|
|
Reading them will give you information about the state of this cpuset:
|
|
the CPUs and Memory Nodes it can use, the processes that are using
|
|
it, its properties. By writing to these files you can manipulate
|
|
the cpuset.
|
|
|
|
Set some flags:
|
|
# /bin/echo 1 > cpu_exclusive
|
|
|
|
Add some cpus:
|
|
# /bin/echo 0-7 > cpus
|
|
|
|
Add some mems:
|
|
# /bin/echo 0-7 > mems
|
|
|
|
Now attach your shell to this cpuset:
|
|
# /bin/echo $$ > tasks
|
|
|
|
You can also create cpusets inside your cpuset by using mkdir in this
|
|
directory.
|
|
# mkdir my_sub_cs
|
|
|
|
To remove a cpuset, just use rmdir:
|
|
# rmdir my_sub_cs
|
|
This will fail if the cpuset is in use (has cpusets inside, or has
|
|
processes attached).
|
|
|
|
Note that for legacy reasons, the "cpuset" filesystem exists as a
|
|
wrapper around the cgroup filesystem.
|
|
|
|
The command
|
|
|
|
mount -t cpuset X /dev/cpuset
|
|
|
|
is equivalent to
|
|
|
|
mount -t cgroup -ocpuset X /dev/cpuset
|
|
echo "/sbin/cpuset_release_agent" > /dev/cpuset/release_agent
|
|
|
|
2.2 Adding/removing cpus
|
|
------------------------
|
|
|
|
This is the syntax to use when writing in the cpus or mems files
|
|
in cpuset directories:
|
|
|
|
# /bin/echo 1-4 > cpus -> set cpus list to cpus 1,2,3,4
|
|
# /bin/echo 1,2,3,4 > cpus -> set cpus list to cpus 1,2,3,4
|
|
|
|
2.3 Setting flags
|
|
-----------------
|
|
|
|
The syntax is very simple:
|
|
|
|
# /bin/echo 1 > cpu_exclusive -> set flag 'cpu_exclusive'
|
|
# /bin/echo 0 > cpu_exclusive -> unset flag 'cpu_exclusive'
|
|
|
|
2.4 Attaching processes
|
|
-----------------------
|
|
|
|
# /bin/echo PID > tasks
|
|
|
|
Note that it is PID, not PIDs. You can only attach ONE task at a time.
|
|
If you have several tasks to attach, you have to do it one after another:
|
|
|
|
# /bin/echo PID1 > tasks
|
|
# /bin/echo PID2 > tasks
|
|
...
|
|
# /bin/echo PIDn > tasks
|
|
|
|
|
|
3. Questions
|
|
============
|
|
|
|
Q: what's up with this '/bin/echo' ?
|
|
A: bash's builtin 'echo' command does not check calls to write() against
|
|
errors. If you use it in the cpuset file system, you won't be
|
|
able to tell whether a command succeeded or failed.
|
|
|
|
Q: When I attach processes, only the first of the line gets really attached !
|
|
A: We can only return one error code per call to write(). So you should also
|
|
put only ONE pid.
|
|
|
|
4. Contact
|
|
==========
|
|
|
|
Web: http://www.bullopensource.org/cpuset
|