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Date:   Mon, 31 Oct 2022 13:57:31 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Andrei Vagin <avagin@google.com>
Cc:     Ingo Molnar <mingo@redhat.com>, Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        linux-kernel@vger.kernel.org, Andrei Vagin <avagin@gmail.com>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Valentin Schneider <vschneid@redhat.com>
Subject: Re: [PATCH] sched: consider WF_SYNC to find idle siblings
Message-ID: <Y1/GO1eWt+oTNA24@hirez.programming.kicks-ass.net>
References: <20221027202603.670616-1-avagin@google.com>
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On Thu, Oct 27, 2022 at 01:26:03PM -0700, Andrei Vagin wrote:
> From: Andrei Vagin <avagin@gmail.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?