Re: [KVM TSC trapping / migration 2/2] Add TSC KHZ MSR

Alexander Graf
2011-01-06T11:40:16Z

On 06.01.2011, at 12:27, Zachary Amsden wrote:

> On 01/06/2011 12:34 AM, Alexander Graf wrote:
>> Am 06.01.2011 um 11:10 schrieb Zachary Amsden<zamsden@redhat.com>:
>>
>>
>>> Use an MSR to allow "soft" migration to hosts which do not support
>>> TSC trapping. Rather than make this a required element of any
>>> migration protocol, we allow the TSC rate to be exported as a data
>>> field (useful in its own right), but we also allow a one time write
>>> of the MSR during VM creation. The result is that for the common
>>> use case, no protocol change is required to communicate TSC rate
>>> to the receiving host.
>>>
>>> This allows administrative tools to configure migration policy
>>> as they see appropriate. Rather than dictate this policy with the
>>> KVM implementation, we properly allow migration to hosts which both
>>> do and do not support setting of the TSC rate on the receiving end.
>>> If it is wished to not support migration to a host which lacks
>>> support for the TSC rate feature, that can be coordinated externally.
>>>
>> Isn't there a real hw equivalent of such a register? It might make more sense to just implement that then.
>>
>>
>
> Unfortunately, no.

Bleks. I couldn't find anything in AMD documentation either. Intel documentation is usually hard to find and incomplete anyways, so maybe something's hiding there - but if it's hidden so well it's no use to implement either.

Alex