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Date:   Tue, 20 Apr 2021 11:48:48 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Stephane Eranian <eranian@google.com>
Cc:     Namhyung Kim <namhyung@kernel.org>, Ingo Molnar <mingo@kernel.org>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Jiri Olsa <jolsa@redhat.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Andi Kleen <ak@linux.intel.com>,
        Ian Rogers <irogers@google.com>,
        Song Liu <songliubraving@fb.com>, Tejun Heo <tj@kernel.org>,
        kernel test robot <lkp@intel.com>,
        Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH v3 1/2] perf/core: Share an event with multiple cgroups
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References: <20210413155337.644993-1-namhyung@kernel.org>
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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.