linux-kernel - Re: [PATCH RFC] reduce runqueue lock contention

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Message-ID: <20101215185929.GA18803@redhat.com>
Date:	Wed, 15 Dec 2010 19:59:29 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Frank Rowand <frank.rowand@...sony.com>
Cc:	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...e.hu>,
	Chris Mason <chris.mason@...cle.com>,
	"axboe@...nel.dk" <axboe@...nel.dk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Mike Galbraith <efault@....de>, tglx <tglx@...utronix.de>
Subject: Re: [PATCH RFC] reduce runqueue lock contention

On 12/13, Frank Rowand wrote:
>
> I have not been able to make sense of the task_running() check in
> try_to_wake_up(), even with that clue.  The try_to_wake_up() code in
> question is:
> ...
>
> What am I missing, or is the task_running() test not needed?

I am afraid I can misuderstood this all, including the question ;)

But, with __ARCH_WANT_UNLOCKED_CTXSW task_running() checks ->oncpu.
However, schedule() drops rq->lock after prev was deactivated but
before it clears prev->oncpu.

Oleg.

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