linux-kernel - [RFC 0/2] perf core: Sharing events with multiple cgroups

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Date:   Wed, 24 Mar 2021 01:21:54 +0900
From:   Namhyung Kim <namhyung@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     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>,
        Stephane Eranian <eranian@...gle.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Ian Rogers <irogers@...gle.com>,
        Song Liu <songliubraving@...com>
Subject: [RFC 0/2] perf core: Sharing events with multiple cgroups

Hello,

This work is to make perf stat more scalable with a lot of cgroups.

Currently we need to open a separate perf_event to count an event in a
cgroup.  For a big machine, this requires lots of events like

  256 cpu x 8 events x 200 cgroups = 409600 events

This is very wasteful and not scalable.  In this case, the perf stat
actually counts exactly same events for each cgroup.  I think we can
just use a single event to measure all cgroups running on that cpu.

So I added new ioctl commands to add per-cgroup counters to an
existing perf_event and to read the per-cgroup counters from the
event.  The per-cgroup counters are updated during the context switch
if tasks' cgroups are different (and no need to change the HW PMU).
It keeps the counters in a hash table with cgroup id as a key.

With this change, average processing time of my internal test workload
which runs tasks in a different cgroup and communicates by pipes
dropped from 11.3 usec to 5.8 usec.

Thanks,
Namhyung

Namhyung Kim (2):
  perf/core: Share an event with multiple cgroups
  perf/core: Support reading group events with shared cgroups

 include/linux/perf_event.h      |  22 ++
 include/uapi/linux/perf_event.h |   2 +
 kernel/events/core.c            | 588 ++++++++++++++++++++++++++++++--
 3 files changed, 585 insertions(+), 27 deletions(-)

-- 
2.31.0.rc2.261.g7f71774620-goog