path: root/kernel
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authorVincent Guittot <vincent.guittot@linaro.org>2018-09-07 09:51:04 +0200
committerIngo Molnar <mingo@kernel.org>2018-09-10 10:13:49 +0200
commitbb3485c8ace6475c269b1aa2da674490f455f412 (patch)
tree7b1a800698793fe038f8537b8b5f84d652018f32 /kernel
parent287cdaac5700c5b8970d739f73d742d863d3e2ca (diff)
sched/fair: Fix load_balance redo for !imbalance
It can happen that load_balance() finds a busiest group and then a busiest rq but the calculated imbalance is in fact 0. In such situation, detach_tasks() returns immediately and lets the flag LBF_ALL_PINNED set. The busiest CPU is then wrongly assumed to have pinned tasks and removed from the load balance mask. then, we redo a load balance without the busiest CPU. This creates wrong load balance situation and generates wrong task migration. If the calculated imbalance is 0, it's useless to try to find a busiest rq as no task will be migrated and we can return immediately. This situation can happen with heterogeneous system or smp system when RT tasks are decreasing the capacity of some CPUs. Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: dietmar.eggemann@arm.com Cc: jhugo@codeaurora.org Link: http://lkml.kernel.org/r/1536306664-29827-1-git-send-email-vincent.guittot@linaro.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel')
1 files changed, 1 insertions, 1 deletions
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index f12d004be6a1..fc9a484ef82b 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8275,7 +8275,7 @@ static struct sched_group *find_busiest_group(struct lb_env *env)
/* Looks like there is an imbalance. Compute it */
calculate_imbalance(env, &sds);
- return sds.busiest;
+ return env->imbalance ? sds.busiest : NULL;
env->imbalance = 0;