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-rw-r--r--kernel/sched/fair.c41
1 files changed, 29 insertions, 12 deletions
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index fe4e0d775375..25dffc03f0f6 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8658,10 +8658,6 @@ static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *s
/*
* Try to use spare capacity of local group without overloading it or
* emptying busiest.
- * XXX Spreading tasks across NUMA nodes is not always the best policy
- * and special care should be taken for SD_NUMA domain level before
- * spreading the tasks. For now, load_balance() fully relies on
- * NUMA_BALANCING and fbq_classify_group/rq to override the decision.
*/
if (local->group_type == group_has_spare) {
if (busiest->group_type > group_fully_busy) {
@@ -8701,16 +8697,37 @@ static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *s
env->migration_type = migrate_task;
lsub_positive(&nr_diff, local->sum_nr_running);
env->imbalance = nr_diff >> 1;
- return;
- }
+ } else {
- /*
- * If there is no overload, we just want to even the number of
- * idle cpus.
- */
- env->migration_type = migrate_task;
- env->imbalance = max_t(long, 0, (local->idle_cpus -
+ /*
+ * If there is no overload, we just want to even the number of
+ * idle cpus.
+ */
+ env->migration_type = migrate_task;
+ env->imbalance = max_t(long, 0, (local->idle_cpus -
busiest->idle_cpus) >> 1);
+ }
+
+ /* Consider allowing a small imbalance between NUMA groups */
+ if (env->sd->flags & SD_NUMA) {
+ unsigned int imbalance_min;
+
+ /*
+ * Compute an allowed imbalance based on a simple
+ * pair of communicating tasks that should remain
+ * local and ignore them.
+ *
+ * NOTE: Generally this would have been based on
+ * the domain size and this was evaluated. However,
+ * the benefit is similar across a range of workloads
+ * and machines but scaling by the domain size adds
+ * the risk that lower domains have to be rebalanced.
+ */
+ imbalance_min = 2;
+ if (busiest->sum_nr_running <= imbalance_min)
+ env->imbalance = 0;
+ }
+
return;
}