linux-kernel - Re: [PATCH 1/2] sched: readd FAIR

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Message-ID: <1337677564.5446.11.camel@marge.simpson.net>
Date:	Tue, 22 May 2012 11:06:04 +0200
From:	Mike Galbraith <efault@....de>
To:	Christian Ehrhardt <ehrhardt@...ux.vnet.ibm.com>
Cc:	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	Heiko Carstens <heiko.carstens@...ibm.com>
Subject: Re: [PATCH 1/2] sched: readd FAIR_SLEEPERS feature

On Tue, 2012-05-22 at 09:11 +0200, Christian Ehrhardt wrote: 
> 
> On 05/21/2012 05:45 PM, Martin Schwidefsky wrote:
> [...]
> > --- a/kernel/sched/features.h
> > +++ b/kernel/sched/features.h
> > @@ -1,3 +1,12 @@
> > +#ifdef CONFIG_SCHED_FAIR_SLEEPERS
> > +/*
> > + * Disregards a certain amount of sleep time (sched_latency_ns) and
> > + * considers the task to be running during that period. This gives it
> > + * a service deficit on wakeup, allowing it to run sooner.
> > + */
> > +SCHED_FEAT(FAIR_SLEEPERS, false)
> > +#endif
> > +
> >   /*
> >    * Only give sleepers 50% of their service deficit. This allows
> >    * them to run sooner, but does not allow tons of sleepers to
> 
> This would be right for s390, but a change to every other architecture.
> As far as I know s390 had custom patches in any distribution supported 
> on s390 to set the default to false (like in your patch), but the 
> upstream default for every other architecture was true.
> 
> I think the patch could look like this to make all happy:
> ...
> +#ifndef CONFIG_S390
> + SCHED_FEAT(FAIR_SLEEPERS, true)
> +#else
> +SCHED_FEAT(FAIR_SLEEPERS, false)
> ...

Um, yeah, default off is a non-starter.. until someone comes up with a
less annoying preemption model that is.

-Mike

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