linux-kernel - Re: Clocksource tsc unstable (delta = -8589361717 ns) in current git

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Date:	Tue, 26 Oct 2010 12:18:56 -0700
From:	john stultz <johnstul@...ibm.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Markus Trippelsdorf <markus@...ppelsdorf.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>
Subject: Re: Clocksource tsc unstable (delta = -8589361717 ns) in current
 git

On Tue, 2010-10-26 at 17:48 +0200, Thomas Gleixner wrote:
> On Tue, 26 Oct 2010, Markus Trippelsdorf wrote:
> > On Tue, Oct 26, 2010 at 03:18:43PM +0200, Borislav Petkov wrote:
> > > otherwise, I don't see anything strange in your dmesg. Unless tglx has a
> > > better idea, I'd ask you to bisect it. 5618 changesets shouldn't be that
> > > much but I don't know, if the issue appears every several hours it could
> > > still be tedious.
> > 
> > That would be a several week long process, as the issue appears ~ every
> > 2 days here on this machine running 24/7.
> 
> There is only a single commit in that area post 2.6.36:
> 
>       8af3c153baf95374eff20a37f00c59a295b52756 
> 
> But I have a hard time how this should make this happen. John ?

Yea, that one doesn't look connected to me.

There have been a few cases that I've seen where we can get false
positives for bad TSCs due to the watchdog clocksource having problems
(or the clocksource watchdog thread getting delayed for such a long time
the watchdog clocksource wraps and we then can't validly compare the two
- although this would be hard to trigger with non-rt kernels).

>>From your dmesg, I'd guess the hpet is the watchdog clocksource, so I'd
be on the lookout for hpet related changes. 

Maybe does reverting 995bd3bb5c78f3ff71339803c0b8337ed36d64fb hide the
issue?

thanks
-john



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