sched: stop wake_affine from causing serious imbalance
Prevent short-running wakers of short-running threads from overloading a single
cpu via wakeup affinity, and wire up disconnected debug option.
Signed-off-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index f0f25fc..08ae848 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -996,25 +996,12 @@
struct task_struct *curr = this_rq->curr;
unsigned long tl = this_load;
unsigned long tl_per_task;
+ int balanced;
- if (!(this_sd->flags & SD_WAKE_AFFINE))
+ if (!(this_sd->flags & SD_WAKE_AFFINE) || !sched_feat(AFFINE_WAKEUPS))
return 0;
/*
- * If the currently running task will sleep within
- * a reasonable amount of time then attract this newly
- * woken task:
- */
- if (sync && curr->sched_class == &fair_sched_class) {
- if (curr->se.avg_overlap < sysctl_sched_migration_cost &&
- p->se.avg_overlap < sysctl_sched_migration_cost)
- return 1;
- }
-
- schedstat_inc(p, se.nr_wakeups_affine_attempts);
- tl_per_task = cpu_avg_load_per_task(this_cpu);
-
- /*
* If sync wakeup then subtract the (maximum possible)
* effect of the currently running task from the load
* of the current CPU:
@@ -1022,8 +1009,24 @@
if (sync)
tl -= current->se.load.weight;
+ balanced = 100*(tl + p->se.load.weight) <= imbalance*load;
+
+ /*
+ * If the currently running task will sleep within
+ * a reasonable amount of time then attract this newly
+ * woken task:
+ */
+ if (sync && balanced && curr->sched_class == &fair_sched_class) {
+ if (curr->se.avg_overlap < sysctl_sched_migration_cost &&
+ p->se.avg_overlap < sysctl_sched_migration_cost)
+ return 1;
+ }
+
+ schedstat_inc(p, se.nr_wakeups_affine_attempts);
+ tl_per_task = cpu_avg_load_per_task(this_cpu);
+
if ((tl <= load && tl + target_load(prev_cpu, idx) <= tl_per_task) ||
- 100*(tl + p->se.load.weight) <= imbalance*load) {
+ balanced) {
/*
* This domain has SD_WAKE_AFFINE and
* p is cache cold in this domain, and
