Re: [RFC PATCH 0/3] directed yield for Pause Loop Exiting

Avi Kivity
2010-12-13T12:42:52Z

On 12/13/2010 02:39 PM, Balbir Singh wrote:
> * Avi Kivity<avi@redhat.com> [2010-12-13 13:57:37]:
>
> > On 12/11/2010 03:57 PM, Balbir Singh wrote:
> > >* Avi Kivity<avi@redhat.com> [2010-12-11 09:31:24]:
> > >
> > >> On 12/10/2010 07:03 AM, Balbir Singh wrote:
> > >> >>
> > >> >> Scheduler people, please flame me with anything I may have done
> > >> >> wrong, so I can do it right for a next version :)
> > >> >>
> > >> >
> > >> >This is a good problem statement, there are other things to consider
> > >> >as well
> > >> >
> > >> >1. If a hard limit feature is enabled underneath, donating the
> > >> >timeslice would probably not make too much sense in that case
> > >>
> > >> What's the alternative?
> > >>
> > >> Consider a two vcpu guest with a 50% hard cap. Suppose the workload
> > >> involves ping-ponging within the guest. If the scheduler decides to
> > >> schedule the vcpus without any overlap, then the throughput will be
> > >> dictated by the time slice. If we allow donation, throughput is
> > >> limited by context switch latency.
> > >>
> > >
> > >If the vpcu holding the lock runs more and capped, the timeslice
> > >transfer is a heuristic that will not help.
> >
> > Why not? as long as we shift the cap as well.
> >
>
> Shifting the cap would break it, no?

The total cap for the guest would remain.

> Anyway, that is something for us
> to keep track of as we add additional heuristics, not a show stopper.

Sure, as long as we see a way to fix it eventually.

--
error compiling committee.c: too many arguments to function