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SubjectRe: [PATCH] 2.6.0 batch scheduling, HT aware
On Tue, 23 Dec 2003 13:57, Nick Piggin wrote:
> Con Kolivas wrote:
> >On Tue, 23 Dec 2003 12:36, Nick Piggin wrote:
> >>Con Kolivas wrote:
> >>>I discussed this with Ingo and that's the sort of thing we thought of.
> >>>Perhaps a relative crossover of 10 dynamic priorities and an absolute
> >>>crossover of 5 static priorities before things got queued together. This
> >>>is really only required for the UP HT case.
> >>
> >>Well I guess it would still be nice for "SMP HT" as well. Hopefully the
> >>code can be generic enough that it would just carry over nicely.
> >
> >I disagree. I can't think of a real world scenario where 2+ physical cpus
> >would benefit from this.
> Well its the same problem. A nice -20 process can still lose 40-55% of its
> performance to a nice 19 process, a figure of 10% is probably too high and
> we'd really want it <= 5% like what happens with a single logical
> processor.

I changed my mind just after I sent that mail. 4 physical cores running three
nice 20 and one nice -20 task gives the nice -20 task only 25% of the total
cpu and 25% to each of the nice 20 tasks.

> >>It does
> >>have complications though because the load balancer would have to be
> >> taught about it, and those architectures that do hardware priorities
> >> probably don't even want it.
> >
> >Probably the simple relative/absolute will have to suffice. However it
> > still doesn't help the fact that running something cpu bound concurrently
> > at nice 0 with something interactive nice 0 is actually slower if you use
> > a UP HT processor in SMP mode instead of UP.
> It will be based on dynamic priorities, possibly with some feedback from
> nice as well, but it probably still won't be perfect and it will probably
> be very complex *cough* hardware priorities *cough* ;)
> I might try to fit it into a more general priority balancing system because
> we currently have similar sorts of failings on regular SMP as well.

I'll keep my eyes peeled. Meanwhile I'll use my ugly patch ;-)


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