Re: [PATCH 2/11] Sched clock paravirt op

[Zachary Amsden <zach@vmware.com>]

Jeremy Fitzhardinge wrote:
> Zachary Amsden wrote:
>   
> > Jeremy Fitzhardinge wrote:
> >     
> > > Zachary Amsden wrote:
> > >  
> > >       
> > > > Scheduled (or available) time and real time are good notions.  Stolen
> > > > time is debatable.  But TSC is basically just always wrong.  That's
> > > > why I don't want to overload the rdtsc operation.     
> > > >         
> > > Well, in the Xen case it is actually guaranteed to be correct and useful
> > > as real time, but that's definitely not something we can expect in
> > > general.  But you're talking specifically about schedulable vcpu time
> > > here, right?
> > >   
> > >       
> > Not schedulable time, scheduled time (schedulable - scheduled) = stolen
> >     
>
> I meant "schedulable" (perhaps "usable" would be better) from the
> guest's perspective: total amount of real cpu time each vcpu gets.  ie:
> (real - schedulable) = stolen.  So I think we're talking about the same
> thing.
>   

Yes, I think so.  The point though, is the for Xen, TSC is real time.  
So it won't do for the scheduler, which must be schedulable time.

Zach

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