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Subject[PATCH v3 07/10] sched/fair: evenly spread tasks when not overloaded
Date
When there is only 1 cpu per group, using the idle cpus to evenly spread
tasks doesn't make sense and nr_running is a better metrics.

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
---
kernel/sched/fair.c | 40 ++++++++++++++++++++++++++++------------
1 file changed, 28 insertions(+), 12 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 15ec38c..a7c8ee6 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8596,18 +8596,34 @@ static struct sched_group *find_busiest_group(struct lb_env *env)
busiest->sum_nr_running > local->sum_nr_running + 1)
goto force_balance;

- if (busiest->group_type != group_overloaded &&
- (env->idle == CPU_NOT_IDLE ||
- local->idle_cpus <= (busiest->idle_cpus + 1)))
- /*
- * If the busiest group is not overloaded
- * and there is no imbalance between this and busiest group
- * wrt idle CPUs, it is balanced. The imbalance
- * becomes significant if the diff is greater than 1 otherwise
- * we might end up to just move the imbalance on another
- * group.
- */
- goto out_balanced;
+ if (busiest->group_type != group_overloaded) {
+ if (env->idle == CPU_NOT_IDLE)
+ /*
+ * If the busiest group is not overloaded (and as a
+ * result the local one too) but this cpu is already
+ * busy, let another idle cpu try to pull task.
+ */
+ goto out_balanced;
+
+ if (busiest->group_weight > 1 &&
+ local->idle_cpus <= (busiest->idle_cpus + 1))
+ /*
+ * If the busiest group is not overloaded
+ * and there is no imbalance between this and busiest
+ * group wrt idle CPUs, it is balanced. The imbalance
+ * becomes significant if the diff is greater than 1
+ * otherwise we might end up to just move the imbalance
+ * on another group. Of course this applies only if
+ * there is more than 1 CPU per group.
+ */
+ goto out_balanced;
+
+ if (busiest->sum_h_nr_running == 1)
+ /*
+ * busiest doesn't have any tasks waiting to run
+ */
+ goto out_balanced;
+ }

force_balance:
/* Looks like there is an imbalance. Compute it */
--
2.7.4
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