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    SubjectRe: Slowdown due to threads bouncing between HT cores
    On Sat, Oct 04, 2014 at 09:50:04AM -0500, Chuck Ebbert wrote:
    > Try playing with /proc/sys/kernel/sched_migration_cost_ns. This sets
    > the number of nanoseconds the kernel will wait before considering
    > moving a thread to another CPU. I have mine set to 50000000.

    I can't get any good effect out of this. I tried both 50 ms (your value) and
    500 ms, and while it seems (by eyeballing the per-cpu display in top) to
    _sometimes_ lock the processes to cores, more often than not, they still
    bounce around between all 40. Worse still, when it _does_, it seems to often
    lock them to hyperthread pairs (e.g., I've seen it put threads only on
    virtual cores 0-9 and 20-29, which means it has all of them on one socket!)

    Notwithstanding top, the benchmarks don't improve; setting cores manually
    with taskset still is much better.

    /* Steinar */
    --
    Homepage: http://www.sesse.net/


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