linux-kernel - Re: [PATCHSET 0/4] perf stat: Add --multiply-cgroup option

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Date:   Thu, 10 Sep 2020 11:15:42 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Stephane Eranian <eranian@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Andi Kleen <andi@...stfloor.org>,
        Ian Rogers <irogers@...gle.com>
Subject: Re: [PATCHSET 0/4] perf stat: Add --multiply-cgroup option

On Tue, Sep 08, 2020 at 01:42:24PM +0900, Namhyung Kim wrote:
> Hello,
> 
> When we profile cgroup events with perf stat, it's very annoying to
> specify events and cgroups on the command line as it requires the
> mapping between events and cgroups.  (Note that perf record can use
> cgroup sampling but it's not usable for perf stat).
> 
> I guess most cases we just want to use a same set of events (N) for
> all cgroups (M), but we need to specify NxM events and NxM cgroups.
> This is not good especially when profiling large number of cgroups:
> say M=200.
> 
> So I added --multiply-cgroup option to make it easy for that case.  It
> will create NxM events from N events and M cgroups.  One more upside
> is that it can handle metrics too.

agreed that it's PITA to use -G option ;-)

> 
> For example, the following example measures IPC metric for 3 cgroups
> 
>   $ cat perf-multi-cgrp.sh
>   #!/bin/sh
>   
>   METRIC=${1:-IPC}
>   CGROUP_DIR=/sys/fs/cgroup/perf_event
>   
>   sudo mkdir $CGROUP_DIR/A $CGROUP_DIR/B $CGROUP_DIR/C
>   
>   # add backgroupd workload for each cgroup
>   echo $$ | sudo tee $CGROUP_DIR/A/cgroup.procs > /dev/null
>   yes > /dev/null &
>   echo $$ | sudo tee $CGROUP_DIR/B/cgroup.procs > /dev/null
>   yes > /dev/null &
>   echo $$ | sudo tee $CGROUP_DIR/C/cgroup.procs > /dev/null
>   yes > /dev/null &
> 
>   # run 'perf stat' in the root cgroup
>   echo $$ | sudo tee $CGROUP_DIR/cgroup.procs > /dev/null
>   perf stat -a -M $METRIC --multiply-cgroup -G A,B,C sleep 1

would it be easier to have new option for this? like:

  perf stat -a -M $METRIC --for-cgroup A,B,C
  perf stat -a -M $METRIC --for-each-cgroup A,B,C
  perf stat -a -M $METRIC --attach-cgroup A,B,C
  perf stat -a -M $METRIC --attach-to-cgroup A,B,C

I'm still not sure how the --multiply-cgroup deals with empty
cgroup A,,C but looks like we don't need this behaviour now?

thanks,
jirka