Subject: Re: -rt IA64 update
From: john stultz <johnstul@us.ibm.com>
To: Ingo Molnar <mingo@elte.hu>
Cc: Simon Derr <Simon.Derr@bull.net>, linux-kernel@vger.kernel.org,
       Thomas Gleixner <tglx@linutronix.de>
In-Reply-To: <20060530061503.GA19870@elte.hu>
References: <Pine.LNX.4.61.0605291356170.14092@openx3.frec.bull.fr>
	 <20060530061503.GA19870@elte.hu>
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Date: Tue, 30 May 2006 07:20:41 -0700
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On Tue, 2006-05-30 at 08:15 +0200, Ingo Molnar wrote:
> * Simon Derr <Simon.Derr@bull.net> wrote:
> > * This kernel, when booting, prints:
> > 
> > 	BUG in check_monotonic_clock at kernel/time/timeofday.c:164
> > 
> > But I think this happens because two get_monotonic_clock() are racing 
> > on two cpus. There is a lock to prevent the race, but it is a seqlock. 
> > That means that it is okay if the race happens since another try will 
> > be attempted, but the message that has been printed on the console 
> > can't be removed, and the user is unnecessarily scared.

Simon, I suspect here you actually have unsynced ITCs, as the
check_monotonic_clock values are all locked w/ spinlocks.

You should probably add a cmpxchg in clocksource_itc_read() where you
currently do the if (last_itc < now), or you'll race on setting
last_itc. Let me know if you still see the issue w/ that fix.


> that too comes from the GTOD patchset. John, should we pick up the 
> latest from -mm?

It would be nice to do so sooner or later. There will probably be a few
regressions as the bits in -mm are more stripped down then the older
code in -rt, but I'd work to fill those holes as they appeared.

Thomas, did you have any thought about the hrt code I sent you?
 
thanks
-john


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