linux-kernel - Re: [sched-devel, patch-rfc] rework of "prioritize non-migratabletasks over migratable ones"

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Message-Id: <1213786064.16944.209.camel@twins>
Date:	Wed, 18 Jun 2008 12:47:44 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Gregory Haskins <ghaskins@...ell.com>,
	Dmitry Adamushko <dmitry.adamushko@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org
Subject: Re: [sched-devel, patch-rfc] rework of "prioritize
	non-migratabletasks over migratable ones"

On Wed, 2008-06-18 at 12:39 +0200, Ingo Molnar wrote:
> * Gregory Haskins <ghaskins@...ell.com> wrote:
> 
> > >>> On Mon, Jun 16, 2008 at  3:17 PM, in message
> > <1213643862.16944.142.camel@...ns>, Peter Zijlstra <a.p.zijlstra@...llo.nl>
> > wrote: 
> > > On Mon, 2008-06-16 at 19:59 +0200, Dmitry Adamushko wrote:
> > > 
> > >> One way or another, we have different aritifacts (and mine have likely
> > >> more) but conceptually, both "violates" POSIX if a strict round-robin
> > >> scheduling is required.
> > > 
> > > http://www.opengroup.org/onlinepubs/009695399/functions/xsh_chap02_08.html#t
> > > ag_02_08_04_01
> > > 
> > > Is quite strict on what FIFO should do, and I know of two points where
> > > we deviate and should work to match.
> > 
> > Thanks for the link, Peter.  When you read that, its pretty clear that 
> > this whole concept violates the standard.  Its probably best to just 
> > revert the patch and be done with it.
> 
> no, there's no spec violation here - the spec is silent on SMP issues.
> 
> the spec should not be read to force a global runqueue for RT tasks. 
> That would be silly beyond imagination.

Sadly, some people do read it like that.

> so ... lets apply Dmitry's nice simplification, hm?

As long as it doesn't wreck the per RQ queue model and only affects the
SMP interaction that would be acceptable I guess.

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