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

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Message-ID: <p73odsccqy5.fsf@verdi.suse.de>
Date:	16 Oct 2006 15:48:02 +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

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.

-Andi
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