linux-kernel - Re: [PATCH RT] sched/core: Avoid__schedule() being called twice, the second in vain

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Message-ID: <20180801111828.ko5t3kgxngv44wg5@linutronix.de>
Date:   Wed, 1 Aug 2018 13:18:28 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Daniel Bristot de Oliveira <bristot@...hat.com>
Cc:     linux-rt-users <linux-rt-users@...r.kernel.org>,
        Clark Williams <williams@...hat.com>,
        Tommaso Cucinotta <tommaso.cucinotta@...up.it>,
        Romulo da Silva de Oliveira <romulo.deoliveira@...c.br>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RT] sched/core: Avoid__schedule() being called twice, the
 second in vain

On 2018-07-30 15:00:00 [+0200], Daniel Bristot de Oliveira wrote:
> Before calling __schedule() to cause a context switch, the schedule()
> function runs sched_submit_work() to dispatch deferred work that was
> postponed to the point that the thread is leaving the processor.
> The function sched_submit_work() checks for the need to wake up a
> kworker; if needed, a kworker thread is awakened. In this context,
> the following behavior takes place.
…
> at line 11, there is nothing to schedule, and so the __schedule() at
> line 18 is called in vain.

I read this as an optimisation for the common case as you put it. 
Applied.

Sebastian