linux-kernel - Re: [PATCH] Fix posix-cpu-timer breakage caused by stale p->last

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Message-Id: <20070301162716.81a53b64.akpm@linux-foundation.org>
Date:	Thu, 1 Mar 2007 16:27:16 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Chuck Ebbert <cebbert@...hat.com>
Cc:	tglx@...utronix.de, Ingo Molnar <mingo@...e.hu>,
	john stultz <johnstul@...ibm.com>,
	Roman Zippel <zippel@...ux-m68k.org>,
	Mike Galbraith <efault@....de>,
	Ken Chen <kenneth.w.chen@...el.com>, balducci@...ts.it,
	LKML <linux-kernel@...r.kernel.org>, Greg KH <greg@...ah.com>
Subject: Re: [PATCH] Fix posix-cpu-timer breakage caused by stale
 p->last_ran value

On Thu, 01 Mar 2007 18:45:14 -0500
Chuck Ebbert <cebbert@...hat.com> wrote:

> Thomas Gleixner wrote:
> > Problem description at:
> > http://bugzilla.kernel.org/show_bug.cgi?id=8048
> > 
> > Commit b18ec80396834497933d77b81ec0918519f4e2a7 
> >     [PATCH] sched: improve migration accuracy
> > optimized the scheduler time calculations, but broke posix-cpu-timers.
> > 
> > The problem is that the p->last_ran value is not updated after a context
> > switch. So a subsequent call to current_sched_time() calculates with a
> > stale p->last_ran value, i.e. accounts the full time, which the task was
> > scheduled away.
> > 
> > Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> > 
> > Index: linux-2.6/kernel/sched.c
> > ===================================================================
> > --- linux-2.6.orig/kernel/sched.c
> > +++ linux-2.6/kernel/sched.c
> > @@ -3566,7 +3566,7 @@ switch_tasks:
> >  
> >  	sched_info_switch(prev, next);
> >  	if (likely(prev != next)) {
> > -		next->timestamp = now;
> > +		next->timestamp = next->last_ran = now;
> >  		rq->nr_switches++;
> >  		rq->curr = next;
> >  		++*switch_count;
> > 
> 
> Is this going to be merged or not??

It just hit mainline.
-
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