sched: rt-group: optimize dequeue_rt_stack
Now that the group hierarchy can have an arbitrary depth the O(n^2) nature
of RT task dequeues will really hurt. Optimize this by providing space to
store the tree path, so we can walk it the other way.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 0a32059..887f5db 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1005,6 +1005,7 @@
unsigned long timeout;
int nr_cpus_allowed;
+ struct sched_rt_entity *back;
#ifdef CONFIG_RT_GROUP_SCHED
struct sched_rt_entity *parent;
/* rq on which this entity is (to be) queued: */
diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index 736fb8f..c2730a5 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -479,26 +479,21 @@
/*
* Because the prio of an upper entry depends on the lower
* entries, we must remove entries top - down.
- *
- * XXX: O(1/2 h^2) because we can only walk up, not down the chain.
*/
static void dequeue_rt_stack(struct task_struct *p)
{
- struct sched_rt_entity *rt_se, *top_se;
+ struct sched_rt_entity *rt_se, *back = NULL;
- /*
- * dequeue all, top - down.
- */
- do {
- rt_se = &p->rt;
- top_se = NULL;
- for_each_sched_rt_entity(rt_se) {
- if (on_rt_rq(rt_se))
- top_se = rt_se;
- }
- if (top_se)
- dequeue_rt_entity(top_se);
- } while (top_se);
+ rt_se = &p->rt;
+ for_each_sched_rt_entity(rt_se) {
+ rt_se->back = back;
+ back = rt_se;
+ }
+
+ for (rt_se = back; rt_se; rt_se = rt_se->back) {
+ if (on_rt_rq(rt_se))
+ dequeue_rt_entity(rt_se);
+ }
}
/*