[RFC PATCH 0/4] Reduce worst-case scanning of runqueues in select_idle_sibling

[Mel Gorman <mgorman@techsingularity.net>]

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
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.

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2.26.2