linux-kernel - Re: [PATCH] hrtimers: Special-case zero length sleeps

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Message-ID: <20120215202221.GA29552@srcf.ucam.org>
Date:	Wed, 15 Feb 2012 20:22:21 +0000
From:	Matthew Garrett <mjg59@...f.ucam.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] hrtimers: Special-case zero length sleeps

On Wed, Feb 15, 2012 at 09:14:30PM +0100, Thomas Gleixner wrote:

> Just for the extended fun of it: The pre hrtimer implementation in
> Linux put the task on sleep as well up to the next jiffies boundary,
> so anything which used sleep(0) on a pre hrtimer kernel was going to
> sleep. That's also the case today when high resolution timers are
> disabled (compile or runtime).
> 
> So anything which relies on sleep(0) as a fast scheduling point is and
> has been broken forever.

Excellent. So the real question is what /should/ sleep(0) do - nothing, 
schedule or sleep for an arbitrary period of time that could be years?

-- 
Matthew Garrett | mjg59@...f.ucam.org
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