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    SubjectRe: [RFC PATCH 0/4] Reduce worst-case scanning of runqueues in select_idle_sibling
    On Mon, 7 Dec 2020 at 10:15, Mel Gorman <mgorman@techsingularity.net> wrote:
    >
    > This is a minimal series to reduce the amount of runqueue scanning in
    > select_idle_sibling in the worst case.
    >
    > Patch 1 removes SIS_AVG_CPU because it's unused.
    >
    > Patch 2 improves the hit rate of p->recent_used_cpu to reduce the amount
    > of scanning. It should be relatively uncontroversial
    >
    > Patch 3-4 scans the runqueues in a single pass for select_idle_core()
    > and select_idle_cpu() so runqueues are not scanned twice. It's
    > a tradeoff because it benefits deep scans but introduces overhead
    > for shallow scans.
    >
    > Even if patch 3-4 is rejected to allow more time for Aubrey's idle cpu mask

    patch 3 looks fine and doesn't collide with Aubrey's work. But I don't
    like patch 4 which manipulates different cpumask including
    load_balance_mask out of LB and I prefer to wait for v6 of Aubrey's
    patchset which should fix the problem of possibly scanning twice busy
    cpus in select_idle_core and select_idle_cpu



    > approach to stand on its own, patches 1-2 should be fine. The main decision
    > with patch 4 is whether select_idle_core() should do a full scan when searching
    > for an idle core, whether it should be throttled in some other fashion or
    > whether it should be just left alone.
    >
    > --
    > 2.26.2
    >

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