Commit ab6c79b8 authored Jan 16, 2018 by Jin Yao Committed by Arnaldo Carvalho de Melo Feb 27, 2018

perf stat: Ignore error thread when enabling system-wide --per-thread



If we execute 'perf stat --per-thread' with non-root account (even set
kernel.perf_event_paranoid = -1 yet), it reports the error:

  jinyao@skl:~$ perf stat --per-thread
  Error:
  You may not have permission to collect system-wide 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
        Ignore mlock limit after perf_event_mlock_kb without CAP_IPC_LOCK
  >= 0: Disallow ftrace function tracepoint by users without CAP_SYS_ADMIN
        Disallow raw tracepoint access by users without CAP_SYS_ADMIN
  >= 1: Disallow CPU event access by users without CAP_SYS_ADMIN
  >= 2: Disallow kernel profiling by users without CAP_SYS_ADMIN

  To make this setting permanent, edit /etc/sysctl.conf too, e.g.:

          kernel.perf_event_paranoid = -1

Perhaps the ptrace rule doesn't allow to trace some processes. But anyway
the global --per-thread mode had better ignore such errors and continue
working on other threads.

This patch will record the index of error thread in perf_evsel__open()
and remove this thread before retrying.

For example (run with non-root, kernel.perf_event_paranoid isn't set):

  jinyao@skl:~$ perf stat --per-thread
  ^C
   Performance counter stats for 'system wide':

         vmstat-3458    6.171984   cpu-clock:u (msec) #  0.000 CPUs utilized
           perf-3670    0.515599   cpu-clock:u (msec) #  0.000 CPUs utilized
         vmstat-3458   1,163,643   cycles:u           #  0.189 GHz
           perf-3670      40,881   cycles:u           #  0.079 GHz
         vmstat-3458   1,410,238   instructions:u     #  1.21  insn per cycle
           perf-3670       3,536   instructions:u     #  0.09  insn per cycle
         vmstat-3458     288,937   branches:u         # 46.814 M/sec
           perf-3670         936   branches:u         #  1.815 M/sec
         vmstat-3458      15,195   branch-misses:u    #  5.26% of all branches
           perf-3670          76   branch-misses:u    #  8.12% of all branches

        12.651675247 seconds time elapsed

Signed-off-by: Jin Yao <yao.jin@linux.intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Kan Liang <kan.liang@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1516117388-10120-1-git-send-email-yao.jin@linux.intel.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

parent 853745f5

tools/perf/builtin-stat.c

+13 −1

Original line number	Diff line number	Diff line
		@@ -637,6 +637,18 @@ try_again:
		if (verbose > 0)
		ui__warning("%s\n", msg);
		goto try_again;
		} else if (target__has_per_thread(&target) &&
		evsel_list->threads &&
		evsel_list->threads->err_thread != -1) {
		/*
		* For global --per-thread case, skip current
		* error thread.
		*/
		if (!thread_map__remove(evsel_list->threads,
		evsel_list->threads->err_thread)) {
		evsel_list->threads->err_thread = -1;
		goto try_again;
		}
		}

		perf_evsel__open_strerror(counter, &target,

tools/perf/util/evsel.c

+3 −0

Original line number	Diff line number	Diff line
		@@ -1915,6 +1915,9 @@ try_fallback:
		goto fallback_missing_features;
		}
		out_close:
		if (err)
		threads->err_thread = thread;

		do {
		while (--thread >= 0) {
		close(FD(evsel, cpu, thread));

tools/perf/util/thread_map.c

+1 −0

Original line number	Diff line number	Diff line
		@@ -32,6 +32,7 @@ static void thread_map__reset(struct thread_map *map, int start, int nr)
		size_t size = (nr - start) * sizeof(map->map[0]);

		memset(&map->map[start], 0, size);
		map->err_thread = -1;
		}

		static struct thread_map thread_map__realloc(struct thread_map map, int nr)

tools/perf/util/thread_map.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -14,6 +14,7 @@ struct thread_map_data {
		struct thread_map {
		refcount_t refcnt;
		int nr;
		int err_thread;
		struct thread_map_data map[];
		};

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