sched: Optimize unused cgroup configuration

When cgroup group scheduling is built in, skip some code paths
if we don't have any (but the root) cgroups configured.

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

diff --git a/kernel/sched.c b/kernel/sched.c
index 26976cd8be0ff5be5b1119d5db1ae4b563a21a33..ca1f76ba77732c61c1463a86ba81e5d5c03d8ccc 100644 (file)
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -1629,8 +1629,14 @@ static int tg_load_down(struct task_group *tg, void *data)
 
 static void update_shares(struct sched_domain *sd)
 {
-       u64 now = cpu_clock(raw_smp_processor_id());
-       s64 elapsed = now - sd->last_update;
+       s64 elapsed;
+       u64 now;
+
+       if (root_task_group_empty())
+               return;
+
+       now = cpu_clock(raw_smp_processor_id());
+       elapsed = now - sd->last_update;
 
        if (elapsed >= (s64)(u64)sysctl_sched_shares_ratelimit) {
                sd->last_update = now;
@@ -1640,6 +1646,9 @@ static void update_shares(struct sched_domain *sd)
 
 static void update_shares_locked(struct rq *rq, struct sched_domain *sd)
 {
+       if (root_task_group_empty())
+               return;
+
        spin_unlock(&rq->lock);
        update_shares(sd);
        spin_lock(&rq->lock);
@@ -1647,6 +1656,9 @@ static void update_shares_locked(struct rq *rq, struct sched_domain *sd)
 
 static void update_h_load(long cpu)
 {
+       if (root_task_group_empty())
+               return;
+
        walk_tg_tree(tg_load_down, tg_nop, (void *)cpu);
 }