linux-kernel - Re: Timer interrupt stops, causes soft lockup

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Message-ID: <20080317154639.GA4102@ucw.cz>
Date:	Mon, 17 Mar 2008 16:46:39 +0100
From:	Pavel Machek <pavel@....cz>
To:	"Joel K. Greene" <joel.greene@...apult.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Timer interrupt stops, causes soft lockup

Hi!

> Of course when time stops progessing forward at a steady pace all
> sorts of Bad Things happen.  
> 
> The clock loop is caused by jiffies not incrementing. It seems that wall
> time updates itself and then resync's with jiffies every ~4s.
> 
> We verified that all spinlocks ( xtime_lock in particular ) were not
> being held, and that the kernel had no reason not to update jiffies.
> Other interrupts continue to fire, so we're not stuck in the timer
> handler.
> 
> So, we went on to look at the PIC. We threw together a little kernel
> module to get some debug info.

Nice debugging.

> We have over 10 systems demonstrating the problem, many in customer
> sites. 

Does nosmp help?

Does noapic/nolapic help?

You may want to try testing with HZ=4000... to show the problem
faster.
							Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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