linux-kernel - Re: RSDL v0.31

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Date:	Thu, 22 Mar 2007 10:34:24 +0100
From:	Mike Galbraith <efault@....de>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>, Willy Tarreau <w@....eu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Xavier Bestel <xavier.bestel@...e.fr>, Mark Lord <lkml@....ca>,
	Al Boldi <a1426z@...ab.com>, Con Kolivas <kernel@...ivas.org>,
	ck@....kolivas.org, Serge Belyshev <belyshev@...ni.sinp.msu.ru>,
	linux-kernel@...r.kernel.org, Nicholas Miell <nmiell@...cast.net>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: RSDL v0.31

On Thu, 2007-03-22 at 10:18 +0100, Ingo Molnar wrote:
> * Mike Galbraith <efault@....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

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