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

Avi Kivity
2010-04-19T10:53:11Z

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.

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