linux-kernel - Re: [bisected] Clocksource tsc unstable git

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Date:	Fri, 29 Oct 2010 10:18:31 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	markus@...ppelsdorf.de
Cc:	john stultz <johnstul@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Borislav Petkov <bp@...64.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"hpa@...ux.intel.com" <hpa@...ux.intel.com>,
	Ingo Molnar <mingo@...e.hu>,
	Andreas Herrmann <andreas.herrmann3@....com>,
	heiko.carstens@...ibm.com, a.p.zijlstra@...llo.nl, avi@...hat.com,
	mtosatti@...hat.com
Subject: Re: [bisected] Clocksource tsc unstable git

On Wed, Oct 27, 2010 at 08:26:08PM +0200, markus@...ppelsdorf.de wrote:
> During my search for a reliable testcase I found out that kvm guests also
> showed random hangs (that didn't happen in v2.6.36) here. These hangs last a
> few seconds each, during which the mouse is not movable at all.
> 
> So I ran git-bisect with this testcase and the result of the bisection is:
> 
> 34f971f6f7988be4d014eec3e3526bee6d007ffa is the first bad commit
> commit 34f971f6f7988be4d014eec3e3526bee6d007ffa
> Author: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Date:   Wed Sep 22 13:53:15 2010 +0200
>

...

>
> Reverting the commit solves the kvm hang issue. (If this issue is
> related to my original tsc problem is of course open for debate, but I
> have a strong hunch it is.)

Well, what do you know, the temporary "slowdown" triggered on my setup
too. After waiting a minute maybe, the machine recovered and guess what
appeared in dmesg:

[44729.650859] Clocksource tsc unstable (delta = -8615263009 ns)
[44729.656229] Switching to clocksource hpet

I've reverted the changeset above and will run without it to check
whether it makes any difference.

-- 
Regards/Gruss,
    Boris.
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