Re: [PATCH 3/7] KVM-HV: KVM Steal time implementation

Gleb Natapov
2011-06-19T13:00:38Z

On Sun, Jun 19, 2011 at 03:35:58PM +0300, Avi Kivity wrote:
> On 06/15/2011 12:09 PM, Gleb Natapov wrote:
> >>
> >> Actually, I'd expect most read/writes to benefit from caching, no?
> >> So why don't we just rename kvm_write_guest_cached() to
> >> kvm_write_guest(), and the few places - if any - that need to force
> >> transversing of the gfn mappings, get renamed to
> >> kvm_write_guest_uncached ?
> >>
> >Good idea. I do not see any places where kvm_write_guest_uncached is
> >needed from a brief look. Avi?
> >
>
> kvm_write_guest_cached() needs something to supply the cache, and
> needs recurring writes to the same location. Neither of these are
> common (for example, instruction emulation doesn't have either).
>
Correct. Missed that. So what about changing steal time to use
kvm_write_guest_cached()?

> >>
> >> If done like you said, time spent on the hypervisor is accounted as
> >> steal time. I don't think it is.
> >I thought that this is the point of a steal time. Running other
> >tasks/guests is a hypervisor overhead too after all :) Also what about
> >time spend serving host interrupts between put/get? It will not be
> >accounted as steal time, correct?
>
> With accurate interrupt time accounting, it should be. Otherwise
> general hypervisor overhead is not steal time.
>
> (i.e. if the host is not overcommitted, steal time should be close to zero).
>

--
Gleb.