linux-kernel - Re: [PATCH 09/10] perf/cputime: Don't stop idle tick if there's live cputime event

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Date:   Thu, 7 Jun 2018 08:45:22 -0700
From:   Andi Kleen <andi@...stfloor.org>
To:     Jiri Olsa <jolsa@...nel.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        lkml <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        David Ahern <dsahern@...il.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Stephane Eranian <eranian@...gle.com>,
        Milian Wolff <milian.wolff@...b.com>,
        Andi Kleen <andi@...stfloor.org>,
        Frederic Weisbecker <frederic@...nel.org>
Subject: Re: [PATCH 09/10] perf/cputime: Don't stop idle tick if there's live
 cputime event

On Thu, Jun 07, 2018 at 12:15:12AM +0200, Jiri Olsa wrote:
> Disable stopping of the idle tick when having live cputime
> event. When the tick is disabled, the idle counts are out
> of date until next tick/update and perf cputime PMU provides
> misleading counts.

I really don't like this. This can totally change performance
(e.g. less Turbo due to less idle) and performance tools shouldn't
change the performance profile drastically.

-Andi