linux-kernel - Re: clocksource changes in 2.6.31

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Message-ID: <alpine.LFD.2.00.0908172032500.2782@localhost.localdomain>
Date:	Mon, 17 Aug 2009 20:34:02 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Stephen Hemminger <shemminger@...tta.com>
cc:	john stultz <johnstul@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: clocksource changes in 2.6.31 - possible regression

On Mon, 17 Aug 2009, Stephen Hemminger wrote:
> On Mon, 17 Aug 2009 11:15:54 -0700
> john stultz <johnstul@...ibm.com> wrote:
> > > > The behavior you describe where you can't switch to the TSC, may be due
> > > > to the TSC disqualification code marking it as non HRT compatible
> > > > (again, I need to double check). While I'm not sure that's really
> > > > correct, as the TSC is fine for HRT, in this case on your box, the TSC
> > > > has been marked as unstable (likely due to being unsynced on old AMD SMP
> > > > systems). There is a real chance that the timekeeping code on your
> > > > system could see the TSC go backwards, calculate a negative time
> > > > interval, and then end up hanging. 
> > > > 
> > > 
> > > TSC was alway stable on this box, and worked fine.  There was no
> > > message in log about TSC instability. The change was bisected
> > > down to that one commit.
> > 
> > But just to clarify, the TSC was never selected as the default
> > clocksource on the box either, right?
> 
> correct.
> 
> I am okay with turning it off on boot command line for my tests,
> but it might be an issue for other users.

Can you please provide a full dmesg of pre 31 and the output of
/sys/.../available_clocksources before you switch to TSC ?

Thanks,

	tglx

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