Messages in this thread | | | From | Vincent Guittot <> | Date | Mon, 7 Dec 2020 16:04:41 +0100 | Subject | Re: [RFC PATCH 0/4] Reduce worst-case scanning of runqueues in select_idle_sibling |
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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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