From 08094828b711dd32de57e9e3314935e19db71b3d Mon Sep 17 00:00:00 2001 From: Arnaldo Carvalho de Melo Date: Thu, 12 May 2016 16:07:47 -0300 Subject: [PATCH] perf evsel: Handle EACCESS + perf_event_paranoid=2 in fallback() Now with the default for the kernel.perf_event_paranoid sysctl being 2 [1] we need to fall back to :u, i.e. to set perf_event_attr.exclude_kernel to 1. Before: [acme@jouet linux]$ perf record usleep 1 Error: You may not have permission to collect stats. Consider tweaking /proc/sys/kernel/perf_event_paranoid, which controls use of the performance events system by unprivileged users (without CAP_SYS_ADMIN). The current value is 2: -1: Allow use of (almost) all events by all users >= 0: Disallow raw tracepoint access by users without CAP_IOC_LOCK >= 1: Disallow CPU event access by users without CAP_SYS_ADMIN >= 2: Disallow kernel profiling by users without CAP_SYS_ADMIN [acme@jouet linux]$ After: [acme@jouet linux]$ perf record usleep 1 [ perf record: Woken up 1 times to write data ] [ perf record: Captured and wrote 0.016 MB perf.data (7 samples) ] [acme@jouet linux]$ perf evlist cycles:u [acme@jouet linux]$ perf evlist -v cycles:u: size: 112, { sample_period, sample_freq }: 4000, sample_type: IP|TID|TIME|PERIOD, disabled: 1, inherit: 1, exclude_kernel: 1, mmap: 1, comm: 1, freq: 1, enable_on_exec: 1, task: 1, sample_id_all: 1, exclude_guest: 1, mmap2: 1, comm_exec: 1 [acme@jouet linux]$ And if the user turns on verbose mode, an explanation will appear: [acme@jouet linux]$ perf record -v usleep 1 Warning: kernel.perf_event_paranoid=2, trying to fall back to excluding kernel samples mmap size 528384B [ perf record: Woken up 1 times to write data ] Looking at the vmlinux_path (8 entries long) Using /lib/modules/4.6.0-rc7+/build/vmlinux for symbols [ perf record: Captured and wrote 0.016 MB perf.data (7 samples) ] [acme@jouet linux]$ [1] 0161028b7c8a ("perf/core: Change the default paranoia level to 2") Reported-by: Ingo Molnar Cc: Adrian Hunter Cc: Andy Lutomirski Cc: David Ahern Cc: Jiri Olsa Cc: Kees Cook Cc: Linus Torvalds Cc: Masami Hiramatsu Cc: Namhyung Kim Cc: Peter Zijlstra Cc: Wang Nan Link: http://lkml.kernel.org/n/tip-b20jmx4dxt5hpaa9t2rroi0o@git.kernel.org Signed-off-by: Arnaldo Carvalho de Melo --- tools/perf/util/evsel.c | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c index a5f339d447cc..645dc1828836 100644 --- a/tools/perf/util/evsel.c +++ b/tools/perf/util/evsel.c @@ -2345,6 +2345,8 @@ int perf_evsel__fprintf(struct perf_evsel *evsel, bool perf_evsel__fallback(struct perf_evsel *evsel, int err, char *msg, size_t msgsize) { + int paranoid; + if ((err == ENOENT || err == ENXIO || err == ENODEV) && evsel->attr.type == PERF_TYPE_HARDWARE && evsel->attr.config == PERF_COUNT_HW_CPU_CYCLES) { @@ -2363,6 +2365,22 @@ bool perf_evsel__fallback(struct perf_evsel *evsel, int err, evsel->attr.config = PERF_COUNT_SW_CPU_CLOCK; zfree(&evsel->name); + return true; + } else if (err == EACCES && !evsel->attr.exclude_kernel && + (paranoid = perf_event_paranoid()) > 1) { + const char *name = perf_evsel__name(evsel); + char *new_name; + + if (asprintf(&new_name, "%s%su", name, strchr(name, ':') ? "" : ":") < 0) + return false; + + if (evsel->name) + free(evsel->name); + evsel->name = new_name; + scnprintf(msg, msgsize, +"kernel.perf_event_paranoid=%d, trying to fall back to excluding kernel samples", paranoid); + evsel->attr.exclude_kernel = 1; + return true; }