linux-kernel - Re: [BUG] long freezes on thinkpad t60

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Date:	Mon, 18 Jun 2007 08:43:43 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	cebbert@...hat.com, chris@...ee.ca, linux-kernel@...r.kernel.org,
	tglx@...utronix.de, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org
Subject: Re: [BUG] long freezes on thinkpad t60


* Miklos Szeredi <miklos@...redi.hu> wrote:

> > could you try the quick hack below, ontop of cfs-v17? It adds two 
> > things to wait_task_inactive():
> > 
> > - a cond_resched() [in case you are running !PREEMPT]
> > 
> > - use MONITOR+MWAIT to monitor memory transactions to the rq->curr
> >   cacheline. This should make the polling loop definitely fair.
> 
> Is it not possible for the mwait to get stuck?

it is - when the other CPU does nothing.

> > If this solves the problem on your box then i'll do a proper fix and 
> > introduce a cpu_relax_memory_change(*addr) type of API to around 
> > monitor/mwait. This patch boots fine on my T60 - but i never saw 
> > your problem.
> 
> Yes, the patch does make the pauses go away.  In fact just the 
> smp_mb() seems to suffice.

cool! Could you send me the smallest patch you tried that still made the 
hangs go away?

	Ingo
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