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

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Date:	Wed, 15 Feb 2012 21:46:27 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Matthew Garrett <mjg59@...f.ucam.org>
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, 15 Feb 2012, Matthew Garrett wrote:

> On Wed, Feb 15, 2012 at 09:30:20PM +0100, Thomas Gleixner wrote:
> > On Wed, 15 Feb 2012, Matthew Garrett wrote:
> > > 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?
> > 
> > Well, I don't expect slack to be set to years and I really don't want
> > to special case sleep(0), because then we might end up discussing
> > special casing usleep(1) or nanosleep(1ns) as well.
> 
> Increasing slack to the seconds range has measureable power management 
> benefits, but there's some code that ends up broken as a result even 
> when they're nominally event driven. I've no problem with us just 
> declaring that code as broken, but it would be less effort to special 
> case it. Application authors do seem to have ended up under the belief 
> that sleep(0) is a meaningful thing to do, and the internet seems to be 
> full of suggestions to use it rather than sched_yield().

The internet is full of crappy suggestions written by absolutely
clueless and advisory resistant morons.

Dammit, we cannot come up with a reasonable definition for special
casing that stuff simply because you cannot draw a clear boundary what
to special case and what not. And there is no sensible definition for
what to do - return right away or go through schedule() or what ever.

sleep(0) is as pointless as sched_yield() and it's about time that we
stop to create a fucking mess in the kernel just because user space
programmers refuse to understand how an operating system works and how
proper programming should be done.

Thanks,

	tglx
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