[PATCH] sched: optimize ttwu vs group scheduling

From: Peter Zijlstra
Date: Mon Mar 09 2009 - 08:56:50 EST


We can avoid the sched domain walk on try_to_wake_up() when we know
there are no groups.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
---
kernel/sched.c | 16 +++++++++++++++-
1 files changed, 15 insertions(+), 1 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index 4414926..188ce3d 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -331,6 +331,13 @@ static DEFINE_PER_CPU(struct rt_rq, init_rt_rq) ____cacheline_aligned_in_smp;
*/
static DEFINE_SPINLOCK(task_group_lock);

+#ifdef CONFIG_SMP
+static int root_task_group_empty(void)
+{
+ return list_empty(&root_task_group->children);
+}
+#endif
+
#ifdef CONFIG_FAIR_GROUP_SCHED
#ifdef CONFIG_USER_SCHED
# define INIT_TASK_GROUP_LOAD (2*NICE_0_LOAD)
@@ -391,6 +398,13 @@ 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)
{
@@ -2363,7 +2377,7 @@ static int try_to_wake_up(struct task_struct *p, unsigned int state, int sync)
sync = 0;

#ifdef CONFIG_SMP
- if (sched_feat(LB_WAKEUP_UPDATE)) {
+ if (sched_feat(LB_WAKEUP_UPDATE) && !root_task_group_empty()) {
struct sched_domain *sd;

this_cpu = raw_smp_processor_id();


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