sched: Fix select_idle_sibling()

Don't bother with selection when the current cpu is idle.  Recent load
balancing changes also make it no longer necessary to check wake_affine()
success before returning the selected sibling, so we now always use it.

Signed-off-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1268301369.6785.36.camel@marge.simson.net>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 10 insertions, 4 deletions

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index d19df5bccfec..0008cc4a1199 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1439,7 +1439,7 @@ static int select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flag
         int cpu = smp_processor_id();
         int prev_cpu = task_cpu(p);
         int new_cpu = cpu;
-        int want_affine = 0;
+        int want_affine = 0, cpu_idle = !current->pid;
         int want_sd = 1;
         int sync = wake_flags & WF_SYNC;
 
@@ -1497,13 +1497,15 @@ static int select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flag
                          * If there's an idle sibling in this domain, make that
                          * the wake_affine target instead of the current cpu.
                          */
-                        if (tmp->flags & SD_SHARE_PKG_RESOURCES)
+                        if (!cpu_idle && tmp->flags & SD_SHARE_PKG_RESOURCES)
                                 target = select_idle_sibling(p, tmp, target);
 
                         if (target >= 0) {
                                 if (tmp->flags & SD_WAKE_AFFINE) {
                                         affine_sd = tmp;
                                         want_affine = 0;
+                                        if (target != cpu)
+                                                cpu_idle = 1;
                                 }
                                 cpu = target;
                         }
@@ -1519,6 +1521,7 @@ static int select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flag
                         sd = tmp;
         }
 
+#ifdef CONFIG_FAIR_GROUP_SCHED
         if (sched_feat(LB_SHARES_UPDATE)) {
                 /*
                  * Pick the largest domain to update shares over
@@ -1532,9 +1535,12 @@ static int select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flag
                 if (tmp)
                         update_shares(tmp);
         }
+#endif
 
-        if (affine_sd && wake_affine(affine_sd, p, sync))
-                return cpu;
+        if (affine_sd) {
+                if (cpu_idle || cpu == prev_cpu || wake_affine(affine_sd, p, sync))
+                        return cpu;
+        }
 
         while (sd) {
                 int load_idx = sd->forkexec_idx;