Commit 4c58f57f authored Jan 04, 2020 by Peng Liu Committed by Peter Zijlstra Jan 17, 2020

sched/fair: Fix sgc->{min,max}_capacity calculation for SD_OVERLAP



commit bf475ce0 ("sched/fair: Add per-CPU min capacity to
sched_group_capacity") introduced per-cpu min_capacity.

commit e3d6d0cb ("sched/fair: Add sched_group per-CPU max capacity")
introduced per-cpu max_capacity.

In the SD_OVERLAP case, the local variable 'capacity' represents the sum
of CPU capacity of all CPUs in the first sched group (sg) of the sched
domain (sd).

It is erroneously used to calculate sg's min and max CPU capacity.
To fix this use capacity_of(cpu) instead of 'capacity'.

The code which achieves this via cpu_rq(cpu)->sd->groups->sgc->capacity
(for rq->sd != NULL) can be removed since it delivers the same value as
capacity_of(cpu) which is currently only used for the (!rq->sd) case
(see update_cpu_capacity()).
An sg of the lowest sd (rq->sd or sd->child == NULL) represents a single
CPU (and hence sg->sgc->capacity == capacity_of(cpu)).

Signed-off-by: Peng Liu <iwtbavbm@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Link: https://lkml.kernel.org/r/20200104130828.GA7718@iZj6chx1xj0e0buvshuecpZ

parent fe71bbb2

kernel/sched/fair.c

+4 −22

Original line number	Diff line number	Diff line
		@@ -7802,29 +7802,11 @@ void update_group_capacity(struct sched_domain *sd, int cpu)
		*/

		for_each_cpu(cpu, sched_group_span(sdg)) {
		struct sched_group_capacity *sgc;
		struct rq *rq = cpu_rq(cpu);

		/*
		* build_sched_domains() -> init_sched_groups_capacity()
		* gets here before we've attached the domains to the
		* runqueues.
		*
		* Use capacity_of(), which is set irrespective of domains
		* in update_cpu_capacity().
		*
		* This avoids capacity from being 0 and
		* causing divide-by-zero issues on boot.
		*/
		if (unlikely(!rq->sd)) {
		capacity += capacity_of(cpu);
		} else {
		sgc = rq->sd->groups->sgc;
		capacity += sgc->capacity;
		}
		unsigned long cpu_cap = capacity_of(cpu);

		min_capacity = min(capacity, min_capacity);
		max_capacity = max(capacity, max_capacity);
		capacity += cpu_cap;
		min_capacity = min(cpu_cap, min_capacity);
		max_capacity = max(cpu_cap, max_capacity);
		}
		} else {
		/*

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