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Subject[tip: sched/core] sched/fair: Skip idle cfs_rq
The following commit has been merged into the sched/core branch of tip:

Commit-ID: fc488ffd4297f661b3e9d7450dcdb9089a53df7c
Gitweb: https://git.kernel.org/tip/fc488ffd4297f661b3e9d7450dcdb9089a53df7c
Author: Vincent Guittot <vincent.guittot@linaro.org>
AuthorDate: Thu, 07 Jan 2021 11:33:23 +01:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Thu, 14 Jan 2021 11:20:10 +01:00

sched/fair: Skip idle cfs_rq

Don't waste time checking whether an idle cfs_rq could be the busiest
queue. Furthermore, this can end up selecting a cfs_rq with a high load
but being idle in case of migrate_load.

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Link: https://lkml.kernel.org/r/20210107103325.30851-2-vincent.guittot@linaro.org
---
kernel/sched/fair.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 40d3ebf..13de7ae 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -9402,8 +9402,11 @@ static struct rq *find_busiest_queue(struct lb_env *env,
if (rt > env->fbq_type)
continue;

- capacity = capacity_of(i);
nr_running = rq->cfs.h_nr_running;
+ if (!nr_running)
+ continue;
+
+ capacity = capacity_of(i);

/*
* For ASYM_CPUCAPACITY domains, don't pick a CPU that could
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