linux-kernel - Re: [PATCH V2 02/13] perf/core: output overhead when sched out from context

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Message-ID: <20161206112107.GK3124@twins.programming.kicks-ass.net>
Date:   Tue, 6 Dec 2016 12:21:07 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     kan.liang@...el.com
Cc:     mingo@...hat.com, acme@...nel.org, linux-kernel@...r.kernel.org,
        alexander.shishkin@...ux.intel.com, tglx@...utronix.de,
        namhyung@...nel.org, jolsa@...nel.org, adrian.hunter@...el.com,
        wangnan0@...wei.com, mark.rutland@....com, andi@...stfloor.org
Subject: Re: [PATCH V2 02/13] perf/core: output overhead when sched out from
 context

On Fri, Dec 02, 2016 at 04:19:10PM -0500, kan.liang@...el.com wrote:
> From: Kan Liang <kan.liang@...el.com>
> 
> Outputing every overhead when it happens is very costly. The accumulated
> time is more meaningful. So the overhead information should be outputted
> at the very end.
> 
> The overhead information is outputted when task is scheduling out or the
> event is going to be disabled.

Why? The context switch stuff can happen very frequently. Doesn't seem
like a good place to add overhead.

> The arch specific overhead is outputted in event pmu delete, when Flag
> PERF_EF_LOG is set.