Re: [PATCH 09/18] Robust TSC compensation

David S. Ahern
2010-07-13T21:42:44Z

On 07/13/10 15:15, Zachary Amsden wrote:

>> What prevents a vcpu from seeing its TSC go backwards, in case the first
>> write in the 5 second window is smaller than the victim vcpu's last
>> visible TSC value ?
>>
>
> Nothing, unfortunately. However, the TSC would already have to be out
> of sync in order for the problem to occur. It can never happen in
> normal circumstances on a stable hardware TSC except in one case;
> migration. During the CPU state transfer phase of migration, however,

What about across processor sockets? Aren't CPUs brought up at different
points such that their TSCs start at different times?

David