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    SubjectRe: [rfc][patch] sched: remove smpnice
    "Siddha, Suresh B" <suresh.b.siddha@intel.com> wrote:
    >
    > On Tue, Feb 07, 2006 at 03:36:17PM -0800, Andrew Morton wrote:
    > > Suresh, Martin, Ingo, Nick and Con: please drop everything, triple-check
    > > and test this:
    > >
    > > From: Peter Williams <pwil3058@bigpond.net.au>
    > >
    > > This is a modified version of Con Kolivas's patch to add "nice" support to
    > > load balancing across physical CPUs on SMP systems.
    >
    > I have couple of issues with this patch.
    >
    > a) on a lightly loaded system, this will result in higher priority job hopping
    > around from one processor to another processor.. This is because of the
    > code in find_busiest_group() which assumes that SCHED_LOAD_SCALE represents
    > a unit process load and with nice_to_bias calculations this is no longer
    > true(in the presence of non nice-0 tasks)
    >
    > My testing showed that 178.galgel in SPECfp2000 is down by ~10% when run with
    > nice -20 on a 4P(8-way with HT) system compared to a nice-0 run.
    >
    > b) On a lightly loaded system, this can result in HT scheduler optimizations
    > being disabled in presence of low priority tasks... in this case, they(low
    > priority ones) can end up running on the same package, even in the presence
    > of other idle packages.. Though this is not as serious as "a" above...
    >

    Thanks very much for discvoring those things.

    That rather leaves us in a pickle wrt 2.6.16.

    It looks like we back out smpnice after all?

    Whatever we do, time is pressing.
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