Re: [PATCH 5/5] KVM: paravirt time source

[Anthony Liguori <anthony-rdkfGonbjUSkNkDKm+mE6A@public.gmane.org>]

Jeremy Fitzhardinge wrote:
> Anthony Liguori wrote:
>   
>> Except that I wanted to change the hypercall to allow querying of real
>> time or "available" time as VMI puts it.
>>     
>
> I see.  You could have an interface like Xen's runstate interface, which
> gives you a breakdown of how long each vcpu spends in each state
> (running, runnable, paused or blocked).  The sum of all of them gives
> you real time, or you can use a subset to work out stolen time
> (runnable+paused), busyness (blocked / (running+runnable+blocked)), etc.
>   

I'll look at that.  Since the vmca is per-vcpu, that may work well.

>> Right now, I'm relying on the PIT but it would be nice to eliminate
>> that.  I'd like to move to something PV so that I can make use of
>> tickless guest kernels.  I'm very open to suggestion and even more
>> open to reusing other people's code :-)
>>     
>
> A simple hypercall interface which says "raise irq X after N ns" is
> probably the easiest way to go.

That's what I was thinking.  The current bit that makes that ugly is 
that you can't really raise an interrupt in the host kernel yet 
(although it will be possible when the in-kernel apic code is merged).  
I could, in theory, implement that interface in userspace but that may 
be ugly.

> Try to avoid the pitfalls of VMI's
> interface in this area, which tries to recycle existing architectural
> interrupt sources for hypervisor timers, and gets into a bit of mess. 
> Xen is relatively clean, but I'm not sure how it would fit into the
> mostly-emulated kvm model.  If you keep things simple, most of the Xen
> clockevent code could be reused with little change.
>   

I think it should work out well.  Thanks for the feedback!

Regards,

Anthony Liguori

>     J
>
>   


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