[lkml]   [2018]   [Jan]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH v2] perf/core: Fix installing cgroup event into cpu
2018-01-24 17:46 GMT+08:00 Peter Zijlstra <>:
> On Wed, Jan 24, 2018 at 05:19:34PM +0800, Lin Xiulei wrote:
>> Sure, and I consider this "OK" works for "What goes wrong if we leave
>> it set?". : )
> It would be good if you inspect the code for the case of leaving
> cpuctx->cgrp set with no cgroup events left -- AND -- put a blurb about
> what you found in your new Changelog.

I have some test cases for this issue, I don't know if it's good to
put those in changelog

reproduction as below

Step 1

Create program for measuring, write below to the file

while True:
sumup = 0
for i in range(10000000):
sumup += i

Step 2

Create cgroup path and run relative program

mkdir /sys/fs/cgroup/perf_event/test1
mkdir /sys/fs/cgroup/perf_event/test2

python &
echo $! > /sys/fs/cgroup/perf_event/test1/cgroup.procs

python &
echo $! > /sys/fs/cgroup/perf_event/test2/cgroup.procs

Step 3

perf stat -e cycles -G test1 -e cycles -G test2 -a sleep 1

You would see output like below


Performance counter stats for 'system wide':

2,161,022,123 cycles test1
138,626,073 cycles test2

1.001858328 seconds time elapsed

The result of test2 is much less than test1, which happens commonly.
Just because of what I mentioned above that a second event couldn't be
activated immediately, that cases some loss

> I suspect it works out and something like perf_cgroup_switch() will fix
> things up for us later, but double check and test.

exactly, the case above wouldn't have any result if no
perf_cgroup_switch() happened.

 \ /
  Last update: 2018-01-24 10:59    [W:0.039 / U:21.364 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site