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

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Message-ID: <4C93E734.4040208@redhat.com>
Date:	Fri, 17 Sep 2010 12:09:56 -1000
From:	Zachary Amsden <zamsden@...hat.com>
To:	Jan Kiszka <jan.kiszka@....de>
CC:	Glauber Costa <glommer@...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

On 09/15/2010 08:27 AM, Jan Kiszka wrote:
> 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
>
>    

I have now reproduced this exactly.  Shouldn't be long before I have a 
solution.

Zach
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