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[RESEND,1/3] sched/fair: fix rounding issue for asym packing

Message ID 1538465199-20176-2-git-send-email-vincent.guittot@linaro.org
State Superseded
Headers show
Series sched/fair: some fixes for asym_packing | expand

Commit Message

Vincent Guittot Oct. 2, 2018, 7:26 a.m. UTC 
When check_asym_packing() is triggered, the imbalance is set to :
busiest_stat.avg_load * busiest_stat.group_capacity / SCHED_CAPACITY_SCALE
busiest_stat.avg_load also comes from a division and the final rounding
can make imbalance slightly lower than the weighted load of the cfs_rq.
But this is enough to skip the rq in find_busiest_queue and prevents asym
migration to happen.

Add 1 to the avg_load to make sure that the targeted cpu will not be
skipped unexpectidly.

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>

---
 kernel/sched/fair.c | 6 ++++++
 1 file changed, 6 insertions(+)

-- 
2.7.4
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Patch

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 6bd142d..0ed99ad2 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7824,6 +7824,12 @@  static inline void update_sg_lb_stats(struct lb_env *env,
 	/* Adjust by relative CPU capacity of the group */
 	sgs->group_capacity = group->sgc->capacity;
 	sgs->avg_load = (sgs->group_load*SCHED_CAPACITY_SCALE) / sgs->group_capacity;
+	/*
+	 * Prevent division rounding to make the computation of imbalance
+	 * slightly less than original value and to prevent the rq to be then
+	 * selected as busiest queue
+	 */
+	sgs->avg_load += 1;
 
 	if (sgs->sum_nr_running)
 		sgs->load_per_task = sgs->sum_weighted_load / sgs->sum_nr_running;