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Subject[PATCH v2] sched/fair: fix sgc->{min,max}_capacity miscalculate
commit bf475ce0a3dd ("sched/fair: Add per-CPU min capacity to
sched_group_capacity") introduced per-cpu min_capacity.

commit e3d6d0cb66f2 ("sched/fair: Add sched_group per-CPU max capacity")
introduced per-cpu max_capacity.

Here, capacity is the accumulated sum of (maybe) many CPUs' capacity.
Compare with capacity to get {min,max}_capacity makes no sense. Instead,
we should compare one by one in each iteration to get
sgc->{min,max}_capacity of the group.

Also, the only CPU in rq->sd->groups should be rq's CPU. Thus,
capacity_of(cpu_of(rq)) should be equal to rq->sd->groups->sgc->capacity.
Code can be simplified by removing the if/else.

Signed-off-by: Peng Liu <iwtbavbm@gmail.com>
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
---
v1: https://lkml.org/lkml/2019/12/30/502

kernel/sched/fair.c | 26 ++++----------------------
1 file changed, 4 insertions(+), 22 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 2d170b5da0e3..e14698a8ee38 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7793,29 +7793,11 @@ 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);
+ unsigned long cpu_cap = capacity_of(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;
- }
-
- min_capacity = min(capacity, min_capacity);
- max_capacity = max(capacity, max_capacity);
+ min_capacity = min(cpu_cap, min_capacity);
+ max_capacity = max(cpu_cap, max_capacity);
+ capacity += cpu_cap;
}
} else {
/*
--
2.17.1
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