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

Balbir Singh
2010-12-11T13:57:27Z

* 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.

--
Three Cheers,
Balbir