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Date:   Sat, 24 Apr 2021 10:30:00 +0100
From:   Mel Gorman <mgorman@suse.de>
To:     Rik van Riel <riel@surriel.com>
Cc:     linux-kernel@vger.kernel.org, kernel-team@fb.com,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Valentin Schneider <valentin.schneider@arm.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@kernel.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>
Subject: Re: [PATCH v4] sched,fair: Skip newidle_balance if a wakeup is
 pending
Message-ID: <20210424093000.GA4171@suse.de>
References: <20210422130236.0bb353df@imladris.surriel.com>
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On Thu, Apr 22, 2021 at 01:02:36PM -0400, Rik van Riel wrote:
> The try_to_wake_up function has an optimization where it can queue
> a task for wakeup on its previous CPU, if the task is still in the
> middle of going to sleep inside schedule().
> 
> Once schedule() re-enables IRQs, the task will be woken up with an
> IPI, and placed back on the runqueue.
> 
> If we have such a wakeup pending, there is no need to search other
> CPUs for runnable tasks. Just skip (or bail out early from) newidle
> balancing, and run the just woken up task.
> 
> For a memcache like workload test, this reduces total CPU use by
> about 2%, proportionally split between user and system time,
> and p99 and p95 application response time by 10% on average.
> The schedstats run_delay number shows a similar improvement.
> 
> Signed-off-by: Rik van Riel <riel@surriel.com>

Acked-by: Mel Gorman <mgorman@suse.de>

-- 
Mel Gorman
SUSE Labs