linux-kernel - Re: x86, vmi: TSC going backwards check in vmi clocksource

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Message-Id: <1235066638.23293.7.camel@alok-dev1>
Date:	Thu, 19 Feb 2009 10:03:58 -0800
From:	Alok Kataria <akataria@...are.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	the arch/x86 maintainers <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Zach Amsden <zach@...are.com>
Subject: Re: x86, vmi: TSC going backwards check in vmi clocksource

On Thu, 2009-02-19 at 03:18 -0800, Ingo Molnar wrote:
> * Alok Kataria <akataria@...are.com> wrote:
> 
> > From: Alok N Kataria <akataria@...are.com>
> > 
> > Similar to the check for TSC going backwards in the TSC 
> > clocksource, we also need this check for VMI clocksource.
> 
> ok. Precisely what kind of bug/symptoms does this fix?

If the read CYCLES_REAL counter value is less than the cycle_last value,
it may result in time jumps.
I also saw some messages about  process being stuck for more than
120sec, which was traced back to this.

Thanks,
Alok
> 
> 	Ingo

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