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    SubjectRe: [RFC PATCH v2 3/6] sched: pack small tasks
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    On Tue, Dec 18, 2012 at 5:53 PM, Vincent Guittot
    <vincent.guittot@linaro.org> wrote:
    > On 17 December 2012 16:24, Alex Shi <alex.shi@intel.com> wrote:
    >>>>>>>> The scheme below tries to summaries the idea:
    >>>>>>>>
    >>>>>>>> Socket | socket 0 | socket 1 | socket 2 | socket 3 |
    >>>>>>>> LCPU | 0 | 1-15 | 16 | 17-31 | 32 | 33-47 | 48 | 49-63 |
    >>>>>>>> buddy conf0 | 0 | 0 | 1 | 16 | 2 | 32 | 3 | 48 |
    >>>>>>>> buddy conf1 | 0 | 0 | 0 | 16 | 16 | 32 | 32 | 48 |
    >>>>>>>> buddy conf2 | 0 | 0 | 16 | 16 | 32 | 32 | 48 | 48 |
    >>>>>>>>
    >>>>>>>> But, I don't know how this can interact with NUMA load balance and the
    >>>>>>>> better might be to use conf3.
    >>>>>>>
    >>>>>>> I mean conf2 not conf3

    >
    > Cyclictest is the ultimate small tasks use case which points out all
    > weaknesses of a scheduler for such kind of tasks.
    > Music playback is a more realistic one and it also shows improvement
    >
    >> granularity or one tick, thus we really don't need to consider task
    >> migration cost. But when the task are not too small, migration is more
    >
    > For which kind of machine are you stating that hypothesis ?

    Seems the biggest argument between us is you didn't want to admit 'not
    too small tasks' exists and that will cause more migrations because
    your patch.

    >> even so they should run in the same socket for power saving
    >> consideration(my power scheduling patch can do this), instead of spread
    >> to all sockets.
    >
    > This is may be good for your scenario and your machine :-)
    > Packing small tasks is the best choice for any scenario and machine.

    That's clearly wrong, I had explained many times, your single buddy
    CPU is impossible packing all tasks for a big machine, like for just
    16 LCPU, while it suppose do.

    Anyway you have right insist your design. and I thought I can not say
    more clear about the scalability issue. I won't judge the patch again.


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