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    SubjectRe: -mm seems significanty slower than mainline on kernbench
    Martin Bligh wrote:
    >>> But I was thinking more about the code that (in the original) handled
    >>> the case where the number of tasks to be moved was less than 1 but
    >>> more than 0 (i.e. the cases where "imbalance" would have been reduced
    >>> to zero when divided by SCHED_LOAD_SCALE). I think that I got that
    >>> part wrong and you can end up with a bias load to be moved which is
    >>> less than any of the bias_prio values for any queued tasks (in
    >>> circumstances where the original code would have rounded up to 1 and
    >>> caused a move). I think that the way to handle this problem is to
    >>> replace 1 with "average bias prio" within that logic. This would
    >>> guarantee at least one task with a bias_prio small enough to be moved.
    >>> I think that this analysis is a strong argument for my original patch
    >>> being the cause of the problem so I'll go ahead and generate a fix.
    >>> I'll try to have a patch available later this morning.
    >> Attached is a patch that addresses this problem. Unlike the
    >> description above it does not use "average bias prio" as that solution
    >> would be very complicated. Instead it makes the assumption that
    >> NICE_TO_BIAS_PRIO(0) is a "good enough" for this purpose as this is
    >> highly likely to be the median bias prio and the median is probably
    >> better for this purpose than the average.
    >> Signed-off-by: Peter Williams <>
    > Doesn't fix the perf issue.

    OK, thanks. I think there's a few more places where SCHED_LOAD_SCALE
    needs to be multiplied by NICE_TO_BIAS_PRIO(0). Basically, anywhere
    that it's added to, subtracted from or compared to a load. In those
    cases it's being used as a scaled version of 1 and we need a scaled
    version of NICE_TO_BIAS_PRIO(0). I'll have another patch later today.

    Peter Williams

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