linux-kernel - Re: [PATCH 1/5] Add a global synchronization point for pvclock

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Date:	Mon, 19 Apr 2010 13:54:12 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Glauber Costa <glommer@...hat.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Zachary Amsden <zamsden@...hat.com>
Subject: Re: [PATCH 1/5] Add a global synchronization point for pvclock

On 04/19/2010 01:51 PM, Peter Zijlstra wrote:
>
>    
>>> Right, so on x86 we have:
>>>
>>> X86_FEATURE_CONSTANT_TSC, which only states that TSC is frequency
>>> independent, not that it doesn't stop in C states and similar fun stuff.
>>>
>>> X86_FEATURE_TSC_RELIABLE, which IIRC should indicate the TSC is constant
>>> and synced between cores.
>>>
>>>
>>>        
>> Sockets and boards too?  (IOW, how reliable is TSC_RELIABLE)?
>>      
> Not sure, IIRC we clear that when the TSC sync test fails, eg when we
> mark the tsc clocksource unusable.
>    

Worrying.  By the time we detect this the guest may already have gotten 
confused by clocks going backwards.

-- 
error compiling committee.c: too many arguments to function

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