linux-kernel - Re: [PATCH v3 1/2] perf/core: Share an event with multiple cgroups

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Message-ID: <YH6jgMWpFXy+pFVP@hirez.programming.kicks-ass.net>
Date:   Tue, 20 Apr 2021 11:48:48 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Stephane Eranian <eranian@...gle.com>
Cc:     Namhyung Kim <namhyung@...nel.org>, Ingo Molnar <mingo@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Ian Rogers <irogers@...gle.com>,
        Song Liu <songliubraving@...com>, Tejun Heo <tj@...nel.org>,
        kernel test robot <lkp@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v3 1/2] perf/core: Share an event with multiple cgroups

On Tue, Apr 20, 2021 at 01:34:40AM -0700, Stephane Eranian wrote:
> The sampling approach will certainly incur more overhead and be at
> risk of losing the ability to
> reconstruct the total counter per-cgroup, unless  you set the period
> for SW_CGROUP_SWITCHES to
> 1. But then, you run the risk of losing samples if the buffer is full
> or sampling is throtlled.
> In some scenarios, we believe the number of context switches between
> cgroup could be quite high (>> 1000/s).
> And on top you would have to add the processing of the samples to
> extract the counts per cgroup. That would require
> a synthesis on cgroup on perf record and some post-processing on perf
> report. We are interested in using the data live
> to make some policy decisions, so a counting approach with perf stat
> will always be best.

Can you please configure your MUA to sanely (re)flow text? The above
random line-breaks are *so* painful to read.