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sched: Avoid unnecessary calculation of load imbalance at clone time

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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
This commit is contained in:
Mel Gorman 2020-11-20 09:06:28 +00:00 committed by Peter Zijlstra
parent abeae76a47
commit 5c339005f8
1 changed files with 5 additions and 3 deletions
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8
kernel/sched/fair.c
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@ -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