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

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Message-ID: <4BCC3617.6050106@redhat.com>
Date:	Mon, 19 Apr 2010 13:53:11 +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 01:49 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.
>>      
> Fun, we also have:
>
> X86_FEATURE_NONSTOP_TSC, which states the thing doesn't stop in C
> states.
>    

All of them? I though tsc stops in some mwait deep REM sleep thing.

So what do we need?  test for both TSC_RELIABLE and NONSTOP_TSC?  IMO 
TSC_RELIABLE should imply NONSTOP_TSC.

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

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