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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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