Commit c917e0f2 authored Mar 12, 2018 by Song Liu Committed by Ingo Molnar Mar 20, 2018

perf/cgroup: Fix child event counting bug



When a perf_event is attached to parent cgroup, it should count events
for all children cgroups:

   parent_group   <---- perf_event
     \
      - child_group  <---- process(es)

However, in our tests, we found this perf_event cannot report reliable
results. Here is an example case:

  # create cgroups
  mkdir -p /sys/fs/cgroup/p/c
  # start perf for parent group
  perf stat -e instructions -G "p"

  # on another console, run test process in child cgroup:
  stressapptest -s 2 -M 1000 & echo $! > /sys/fs/cgroup/p/c/cgroup.procs

  # after the test process is done, stop perf in the first console shows

       <not counted>      instructions              p

The instruction should not be "not counted" as the process runs in the
child cgroup.

We found this is because perf_event->cgrp and cpuctx->cgrp are not
identical, thus perf_event->cgrp are not updated properly.

This patch fixes this by updating perf_cgroup properly for ancestor
cgroup(s).

Reported-by: Ephraim Park <ephiepark@fb.com>
Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: <jolsa@redhat.com>
Cc: <kernel-team@fb.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Link: http://lkml.kernel.org/r/20180312165943.1057894-1-songliubraving@fb.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 320b0651

kernel/events/core.c

+16 −5

Original line number	Diff line number	Diff line
		@@ -724,9 +724,15 @@ static inline void __update_cgrp_time(struct perf_cgroup *cgrp)

		static inline void update_cgrp_time_from_cpuctx(struct perf_cpu_context *cpuctx)
		{
		struct perf_cgroup *cgrp_out = cpuctx->cgrp;
		if (cgrp_out)
		__update_cgrp_time(cgrp_out);
		struct perf_cgroup *cgrp = cpuctx->cgrp;
		struct cgroup_subsys_state *css;

		if (cgrp) {
		for (css = &cgrp->css; css; css = css->parent) {
		cgrp = container_of(css, struct perf_cgroup, css);
		__update_cgrp_time(cgrp);
		}
		}
		}

		static inline void update_cgrp_time_from_event(struct perf_event *event)
		@@ -754,6 +760,7 @@ perf_cgroup_set_timestamp(struct task_struct *task,
		{
		struct perf_cgroup *cgrp;
		struct perf_cgroup_info *info;
		struct cgroup_subsys_state *css;

		/*
		* ctx->lock held by caller
		@@ -764,9 +771,13 @@ perf_cgroup_set_timestamp(struct task_struct *task,
		return;

		cgrp = perf_cgroup_from_task(task, ctx);

		for (css = &cgrp->css; css; css = css->parent) {
		cgrp = container_of(css, struct perf_cgroup, css);
		info = this_cpu_ptr(cgrp->info);
		info->timestamp = ctx->timestamp;
		}
		}

		static DEFINE_PER_CPU(struct list_head, cgrp_cpuctx_list);

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