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    SubjectRe: [RFC PATCH 0/2] sched: simplify the select_task_rq_fair()
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    On Wed, 2013-01-23 at 16:30 +0800, Michael Wang wrote: 
    > On 01/23/2013 04:20 PM, Mike Galbraith wrote:
    > > On Wed, 2013-01-23 at 15:10 +0800, Michael Wang wrote:
    > >> On 01/23/2013 02:28 PM, Mike Galbraith wrote:
    > >
    > >>> Abbreviated test run:
    > >>> Tasks jobs/min jti jobs/min/task real cpu
    > >>> 640 158044.01 81 246.9438 24.54 577.66 Wed Jan 23 07:14:33 2013
    > >>> 1280 50434.33 39 39.4018 153.80 5737.57 Wed Jan 23 07:17:07 2013
    > >>> 2560 47214.07 34 18.4430 328.58 12715.56 Wed Jan 23 07:22:36 2013
    > >>
    > >> So still not works... and not going to balance path while waking up will
    > >> fix it, looks like that's the only choice if no error on balance path
    > >> could be found...benchmark wins again, I'm feeling bad...
    > >>
    > >> I will conclude the info we collected and make a v3 later.
    > >
    > > FWIW, I hacked virgin to do full balance if an idle CPU was not found,
    > > leaving the preference to wake cache affine intact though, turned on
    > > WAKE_BALANCE in all domains, and it did not collapse. In fact, the high
    > > load end, where the idle search will frequently be a waste of cycles,
    > > actually improved a bit. Things that make ya go hmmm.
    >
    > Oh, does that means the old balance path is good while the new is really
    > broken, I mean, compared this with the previously results, could we say
    > that all the collapse was just caused by the change of balance path?

    That's a good supposition. I'll see if it holds.

    Next, I'm going to try ripping select_idle_sibling() to tiny shreds,
    twiddle the balance path a little to see if I can get rid of the bad
    stuff for tbench, maybe make some good stuff for pgbench and ilk, ilk
    _maybe_ including heavy duty remote network type loads.

    There's gonna be some violent axe swinging here shortly.

    -Mike



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