linux-kernel - Re: [KVM timekeeping 10/35] Fix deep C-state TSC desynchronization

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Date:	Wed, 15 Sep 2010 20:27:14 +0200
From:	Jan Kiszka <jan.kiszka@....de>
To:	Glauber Costa <glommer@...hat.com>
CC:	Zachary Amsden <zamsden@...hat.com>, kvm@...r.kernel.org,
	Avi Kivity <avi@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	John Stultz <johnstul@...ibm.com>, linux-kernel@...r.kernel.org
Subject: Re: [KVM timekeeping 10/35] Fix deep C-state TSC desynchronization

Am 15.09.2010 14:32, Glauber Costa wrote:
> On Wed, Sep 15, 2010 at 10:09:33AM +0200, Jan Kiszka wrote:
>>> In any case, I'll proceed with the forcing of unstable TSC and HPET
>>> clocksource and see what happens.
>>
>> I tried that before, but it did not trigger the issue that kvm-clock
>> guests no longer boot properly. This only happens if the TSC is marked
>> unstable.
> 
> even artificially marked unstable ?
> 

Yes. As soon as I hack tsc_unstable to 1, things go wrong. When I hack
it back to 0, guest that wants kvm-clock boots again and seem to run fine.

This is issue #2, I guess. Issue #2 remains that the TSC is marked
unstable. I have the feeling that this is bogus, maybe due to lacking
suspend/resume awareness? The tsc clocksource does

	clocksource_tsc.cycle_last = 0;

on resume...

Jan


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