Re: [RFC] CPU hard limits

Balbir Singh
2009-06-05T09:41:06Z

* Bharata B Rao <bharata@linux.vnet.ibm.com> [2009-06-05 11:01:59]:

> On Fri, Jun 05, 2009 at 01:27:55PM +0800, Balbir Singh wrote:
> > * Avi Kivity <avi@redhat.com> [2009-06-05 08:21:43]:
> >
> > > Balbir Singh wrote:
> > >>> But then there is no other way to make a *guarantee*, guarantees come
> > >>> at a cost of idling resources, no? Can you show me any other
> > >>> combination that will provide the guarantee and without idling the
> > >>> system for the specified guarantees?
> > >>>
> > >>
> > >> OK, I see part of your concern, but I think we could do some
> > >> optimizations during design. For example if all groups have reached
> > >> their hard-limit and the system is idle, should we do start a new hard
> > >> limit interval and restart, so that idleness can be removed. Would
> > >> that be an acceptable design point?
> > >
> > > I think so. Given guarantees G1..Gn (0 <= Gi <= 1; sum(Gi) <= 1), and a
> > > cpu hog running in each group, how would the algorithm divide resources?
> > >
> >
> > As per the matrix calculation, but as soon as we reach an idle point,
> > we redistribute the b/w and start a new quantum so to speak, where all
> > groups are charged up to their hard limits.
>
> But could there be client models where you are required to strictly
> adhere to the limit within the bandwidth and not provide more (by advancing
> the bandwidth period) in the presence of idle cycles ?
>

Good point, I think so, so I think there is should be a good default
and configurable for the other case.

--
Balbir