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

Avi Kivity
2010-04-19T10:49:09Z

On 04/19/2010 01:46 PM, Peter Zijlstra wrote:
> On Sat, 2010-04-17 at 21:48 +0300, Avi Kivity wrote:
>
>>> After this patch is applied, I don't see a single warp in time during 5 days
>>> of execution, in any of the machines I saw them before.
>>>
>>>
>>>
>> Please define a cpuid bit that makes this optional. When we eventually
>> enable it in the future, it will allow a wider range of guests to enjoy it.
>>
> 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)?

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