Re: KVM PMU virtualization

Avi Kivity
2010-02-26T13:56:42Z

On 02/26/2010 03:37 PM, Jes Sorensen wrote:
> On 02/26/10 14:31, Ingo Molnar wrote:
>> You are missing two big things wrt. compatibility here:
>>
>> 1) The first upgrade overhead a one time overhead only.
>>
>> 2) Once a Linux guest has upgraded, it will work in the future,
>> with _any_
>> future CPU - _without_ having to upgrade the guest!
>>
>> Dont you see the advantage of that? You can instrument an old system
>> on new
>> hardware, without having to upgrade that guest for the new CPU support.
>
> That would only work if you are guaranteed to be able to emulate old
> hardware on new hardware. Not going to be feasible, so then we are in a
> real mess.
>

That actually works on the Intel-only architectural pmu. I'm beginning
to like it more and more.

--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.