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Subject[PATCH v4 1/3] sched/fair: fix rounding issue for asym packing
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When check_asym_packing() is triggered, the imbalance is set to :
busiest_stat.avg_load * busiest_stat.group_capacity / SCHED_CAPACITY_SCALE
But busiest_stat.avg_load equals :
sgs->group_load *SCHED_CAPACITY_SCALE / sgs->group_capacity
These divisions can generate a rounding that will 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.

Directly set imbalance to busiest's sgs->group_load to remove the rounding.

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
---
kernel/sched/fair.c | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index ca46964..1e4bed4 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8476,9 +8476,7 @@ static int check_asym_packing(struct lb_env *env, struct sd_lb_stats *sds)
if (sched_asym_prefer(busiest_cpu, env->dst_cpu))
return 0;

- env->imbalance = DIV_ROUND_CLOSEST(
- sds->busiest_stat.avg_load * sds->busiest_stat.group_capacity,
- SCHED_CAPACITY_SCALE);
+ env->imbalance = sds->busiest_stat.group_load;

return 1;
}
--
2.7.4
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