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    SubjectRe: [patch] smpnice: don't consider sched groups which are lightly loaded for balancing
    Andrew Morton wrote:
    > "Siddha, Suresh B" <> wrote:
    >> updated patch appended. thanks.
    > Where are we up to with smpnice now? Are there still any known
    > regressions/problems/bugs/etc?

    One more change to move_tasks() is required to address an issue raised
    by Suresh w.r.t. the possibility unnecessary movement of the highest
    priority task from the busiest queue (possible because of the
    active/expired array mechanism). I hope to forward a patch for this
    later today.

    After that the only thing I would like to do at this stage is modify
    try_to_wake_up() so that it tries harder to distribute high priority
    tasks across the CPUs. I wouldn't classify this as absolutely necessary
    as it's really just a measure that attempts to reduce latency for high
    priority tasks as it should get them onto a CPU more quickly than just
    sticking them anywhere and waiting for load balancing to kick in if
    they've been put on a CPU with a higher priority task already running.
    Also it's only really necessary when there a lot of high priority tasks
    running. So this isn't urgent and probably needs to be coordinated with
    Ingo's RT load balancing stuff anyway.

    > Has sufficient testing been done for us to
    > know this?

    I run smpnice kernels on all of my SMP machines all of the time. But I
    don't have anything with more than 2 CPUs so I've been relying on their
    presence in -mm to get wider testing on larger machines.

    I think that once this patch and the move_tasks() one that I'll forward
    later today are incorporated we should have something that (although not
    perfect) works pretty well. Neither of these changes should cause a
    behavioural change in the case where all tasks are nice==0.

    As load balancing is inherently probabilistic I don't think that we
    should hold out for "perfect".

    Peter Williams

    "Learning, n. The kind of ignorance distinguishing the studious."
    -- Ambrose Bierce
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