linux-kernel - Re: [PATCH] sched: consider WF

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Date:   Mon, 31 Oct 2022 13:57:31 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Andrei Vagin <avagin@...gle.com>
Cc:     Ingo Molnar <mingo@...hat.com>, Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        linux-kernel@...r.kernel.org, Andrei Vagin <avagin@...il.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>
Subject: Re: [PATCH] sched: consider WF_SYNC to find idle siblings

On Thu, Oct 27, 2022 at 01:26:03PM -0700, Andrei Vagin wrote:
> From: Andrei Vagin <avagin@...il.com>
> 
> WF_SYNC means that the waker goes to sleep after wakeup, so the current
> cpu can be considered idle if the waker is the only process that is
> running on it.
> 
> The perf pipe benchmark shows that this change reduces the average time
> per operation from 8.8 usecs/op to 3.7 usecs/op.
> 
> Before:
>  $ ./tools/perf/perf bench sched pipe
>  # Running 'sched/pipe' benchmark:
>  # Executed 1000000 pipe operations between two processes
> 
>      Total time: 8.813 [sec]
> 
>        8.813985 usecs/op
>          113456 ops/sec
> 
> After:
>  $ ./tools/perf/perf bench sched pipe
>  # Running 'sched/pipe' benchmark:
>  # Executed 1000000 pipe operations between two processes
> 
>      Total time: 3.743 [sec]
> 
>        3.743971 usecs/op
>          267096 ops/sec

But what; if anything, does it do for the myrad of other benchmarks we
run?