sched: Optimize cgroup vs wakeup a bit

We don't need to call update_shares() for each domain we iterate,
just got the largets one.

However, we should call it before wake_affine() as well, so that
that can use up-to-date values too.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/sched.c

@@ -376,13 +376,6 @@ static inline void set_task_rq(struct task_struct *p, unsigned int cpu)
 
 #else
 
-#ifdef CONFIG_SMP
-static int root_task_group_empty(void)
-{
-	return 1;
-}
-#endif
-
 static inline void set_task_rq(struct task_struct *p, unsigned int cpu) { }
 static inline struct task_group *task_group(struct task_struct *p)
 {

kernel/sched_fair.c

@@ -1348,7 +1348,7 @@ find_idlest_cpu(struct sched_group *group, struct task_struct *p, int this_cpu)
  */
 static int select_task_rq_fair(struct task_struct *p, int sd_flag, int flags)
 {
-	struct sched_domain *tmp, *sd = NULL;
+	struct sched_domain *tmp, *shares = NULL, *sd = NULL;
 	int cpu = smp_processor_id();
 	int prev_cpu = task_cpu(p);
 	int new_cpu = cpu;
@@ -1387,22 +1387,14 @@ static int select_task_rq_fair(struct task_struct *p, int sd_flag, int flags)
 				break;
 		}
 
-		switch (sd_flag) {
-		case SD_BALANCE_WAKE:
-			if (!sched_feat(LB_WAKEUP_UPDATE))
-				break;
-		case SD_BALANCE_FORK:
-		case SD_BALANCE_EXEC:
-			if (root_task_group_empty())
-				break;
-			update_shares(tmp);
-		default:
-			break;
-		}
-
 		if (want_affine && (tmp->flags & SD_WAKE_AFFINE) &&
 		    cpumask_test_cpu(prev_cpu, sched_domain_span(tmp))) {
 
+			if (sched_feat(LB_SHARES_UPDATE)) {
+				update_shares(tmp);
+				shares = tmp;
+			}
+
 			if (wake_affine(tmp, p, sync)) {
 				new_cpu = cpu;
 				goto out;
@@ -1417,6 +1409,9 @@ static int select_task_rq_fair(struct task_struct *p, int sd_flag, int flags)
 		sd = tmp;
 	}
 
+	if (sd && sd != shares && sched_feat(LB_SHARES_UPDATE))
+		update_shares(sd);
+
 	while (sd) {
 		struct sched_group *group;
 		int weight;

kernel/sched_features.h

@@ -107,7 +107,7 @@ SCHED_FEAT(ARCH_POWER, 0)
 SCHED_FEAT(HRTICK, 0)
 SCHED_FEAT(DOUBLE_TICK, 0)
 SCHED_FEAT(LB_BIAS, 1)
-SCHED_FEAT(LB_WAKEUP_UPDATE, 1)
+SCHED_FEAT(LB_SHARES_UPDATE, 1)
 SCHED_FEAT(ASYM_EFF_LOAD, 1)
 
 /*