linux-kernel - Re: [PATCH] i386 Time: Avoid PIT SMP lockups

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Message-Id: <200610162042.27292.ak@suse.de>
Date:	Mon, 16 Oct 2006 20:42:27 +0200
From:	Andi Kleen <ak@...e.de>
To:	Andrew Morton <akpm@...l.org>
Cc:	lkml <linux-kernel@...r.kernel.org>, johnstul@...ibm.com
Subject: Re: [PATCH] i386 Time: Avoid PIT SMP lockups

On Monday 16 October 2006 20:39, Andrew Morton wrote:
> On 16 Oct 2006 15:48:02 +0200
> Andi Kleen <ak@...e.de> wrote:
> 
> > Andrew Morton <akpm@...l.org> writes:
> > > 
> > > Is there any actual need to hold xtime_lock while doing the port IO?  I'd
> > > have thought it would suffice to do
> > > 
> > > 	temp = port_io
> > > 	write_seqlock(xtime_lock);
> > > 	xtime = muck_with(temp);
> > > 	write_sequnlock(xtime_lock);
> > > 
> > > ?
> > 
> > That would be a good idea in general. The trouble is just that whatever race
> > is there will be still there then, just harder to trigger (so instead of 
> > every third boot it will muck up every 6 weeks). Not sure that is
> > a real improvement.
> > 
> 
> Confused.  What race are you referring to?

Sorry s/race/starvation/

> 
> This is addressing a starvation problem which is due to the slowness of the
> port-io (iirc).

Is it just sure to go away when the critical section is shorter?

-Andi


 
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