linux-kernel - [PATCH] sched/fair: fix sgc->{min,max}

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Date:   Tue, 31 Dec 2019 11:51:22 +0800
From:   Peng Liu <iwtbavbm@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        qais.yousef@....com, morten.rasmussen@....com
Subject: [PATCH] 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.

sgc->capacity is the *SUM* of all CPU's capacity in the group.
sgc->{min,max}_capacity are the sg per-cpu variables. Compare with
sgc->capacity to get sgc->{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.

Signed-off-by: Peng Liu <iwtbavbm@...il.com>
---
 kernel/sched/fair.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 2d170b5da0e3..97b164fcda93 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7795,6 +7795,7 @@ 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 cap;
 
 			/*
 			 * build_sched_domains() -> init_sched_groups_capacity()
@@ -7808,14 +7809,16 @@ void update_group_capacity(struct sched_domain *sd, int cpu)
 			 * causing divide-by-zero issues on boot.
 			 */
 			if (unlikely(!rq->sd)) {
-				capacity += capacity_of(cpu);
+				cap = capacity_of(cpu);
+				capacity += cap;
+				min_capacity = min(cap, min_capacity);
+				max_capacity = max(cap, max_capacity);
 			} else {
 				sgc = rq->sd->groups->sgc;
 				capacity += sgc->capacity;
+				min_capacity = min(sgc->min_capacity, min_capacity);
+				max_capacity = max(sgc->max_capacity, max_capacity);
 			}
-
-			min_capacity = min(capacity, min_capacity);
-			max_capacity = max(capacity, max_capacity);
 		}
 	} else  {
 		/*
-- 
2.17.1