Commit 5c339005 authored Nov 20, 2020 by Mel Gorman Committed by Peter Zijlstra Nov 24, 2020

sched: Avoid unnecessary calculation of load imbalance at clone time



In find_idlest_group(), the load imbalance is only relevant when the group
is either overloaded or fully busy but it is calculated unconditionally.
This patch moves the imbalance calculation to the context it is required.
Technically, it is a micro-optimisation but really the benefit is avoiding
confusing one type of imbalance with another depending on the group_type
in the next patch.

No functional change.

Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lkml.kernel.org/r/20201120090630.3286-3-mgorman@techsingularity.net

parent abeae76a

kernel/sched/fair.c

+5 −3

Original line number	Diff line number	Diff line
		@@ -8777,9 +8777,6 @@ find_idlest_group(struct sched_domain sd, struct task_struct p, int this_cpu)
		.group_type = group_overloaded,
		};

		imbalance = scale_load_down(NICE_0_LOAD) *
		(sd->imbalance_pct-100) / 100;

		do {
		int local_group;

		@@ -8833,6 +8830,11 @@ find_idlest_group(struct sched_domain sd, struct task_struct p, int this_cpu)
		switch (local_sgs.group_type) {
		case group_overloaded:
		case group_fully_busy:

		/* Calculate allowed imbalance based on load */
		imbalance = scale_load_down(NICE_0_LOAD) *
		(sd->imbalance_pct-100) / 100;

		/*
		* When comparing groups across NUMA domains, it's possible for
		* the local domain to be very lightly loaded relative to the

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