Re: [RFC] Paravirt timer for KVM

Avi Kivity
2007-10-16T07:31:58Z

Glauber de Oliveira Costa wrote:
> On 10/15/07, Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org> wrote:
>
>> If we want to make the clocksource useful for Windows we need to go
>> through the apic as that will allow the TPR to mask the interrupt when
>> Windows isn't ready to receive it. However I don't know whether it is
>> possible to integrate a paravirt clocksource into Windows.
>>
>
> My politically-correct side told me to say that the solution that
> works also in Windows is the best one ;-)
>
>

In this case, I'm not at all sure Windows can benefit from a paravirt
timesource, so it might be better to concentrate on Linux. I'll ask the
Windows people here.

>> For Linux, we might as well go further and provide a completely
>> paravirtualized irqchip instead of trying to integrate a paravirtualized
>> clocksource into a fullyvirtualized irqchip.
>>
>>
>
> Yes, definitely. In your opinion, what's the size of the gap between
> the "we can", and the "we should" here?
>

At present the APIC requires an exit for each level-triggered interrupt.
We could reduce the number of exits to zero given sufficient cleverness.
This would be beneficial to non-streaming I/O workloads.

So yes, I think it's worthwhile.

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