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Subject: Re: RSDL v0.31
From: Mike Galbraith <efault@gmx.de>
To: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>, Willy Tarreau <w@1wt.eu>,
       Linus Torvalds <torvalds@linux-foundation.org>,
       Xavier Bestel <xavier.bestel@free.fr>, Mark Lord <lkml@rtr.ca>,
       Al Boldi <a1426z@gawab.com>, Con Kolivas <kernel@kolivas.org>,
       ck@vds.kolivas.org, Serge Belyshev <belyshev@depni.sinp.msu.ru>,
       linux-kernel@vger.kernel.org, Nicholas Miell <nmiell@comcast.net>,
       Andrew Morton <akpm@linux-foundation.org>
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Date: Thu, 22 Mar 2007 10:34:24 +0100
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On Thu, 2007-03-22 at 10:18 +0100, Ingo Molnar wrote:
> * Mike Galbraith <efault@gmx.de> wrote:
> 
> > Actually, the numbers are an interesting curiosity point, but not as 
> > interesting as the fact that the deadline mechanism isn't kicking in.
> 
> it's not just the scheduling accounting being off, RSDL also seems to be 
> accessing stale data here:
> 
> > >From pull_task():
> > 	/*
> > 	 * If this task has already been running on src_rq this priority
> > 	 * cycle, make the new runqueue think it has been on its cycle
> > 	 */
> > 	if (p->rotation == src_rq->prio_rotation)
> > 		p->rotation = this_rq->prio_rotation;
> > 
> > The intent here is clearly that this task continue on the new cpu as
> > if nothing has happened.  However, when the task was dequeued,
> > p->array was left as it was, points to the last place it was queued.
> > Stale data.
> 
> it might point to a hot-unplugged CPU's runqueue as well. Which might 
> work accidentally, but we want this fixed nevertheless.

Erk!  I mentioned to Con offline that I've seen RSDL bring up only one
of my two (halves of a) penguins a couple three times out of a zillion
boots.  Maybe that's why?

	-Mike