linux-kernel - Re: [PATCH/RFC] wait_for_completion

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Message-ID: <20131118174902.312d8fa6@lwn.net>
Date:	Mon, 18 Nov 2013 17:49:02 -0700
From:	Jonathan Corbet <corbet@....net>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	NeilBrown <neilb@...e.de>, Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	lkml <linux-kernel@...r.kernel.org>,
	"Dr. H. Nikolaus Schaller" <hns@...delico.com>,
	Marek Belisko <marek@...delico.com>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>
Subject: Re: [PATCH/RFC] wait_for_completion_timeout() considered harmful.

On Tue, 19 Nov 2013 00:42:09 +0100
Peter Zijlstra <peterz@...radead.org> wrote:

> I briefly talked to Thomas about this earlier today and we need to fix
> this at a lower level -- the quick 'n dirty solution is to add 1 jiffy
> down in the timer-wheel when we enqueue these things.

That can lead to situations like the one I encountered years ago where
msleep(1) would snooze for 20ms.  I didn't get much love for my idea of
switching msleep() to hrtimers back then, but I still think it might be be
better to provide the resolution that the interface appears to promise.

jon
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