sched: Fix select_idle_sibling()

commit 8b911acdf08477c059d1c36c21113ab1696c612b upstream

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index f719dfabf78e5ecfa184b415c248c6021bdb7970..76d9dc0d6ba05e9b691ce33ac283d070ba95170e 100644 (file)
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1432,7 +1432,7 @@ select_task_rq_fair(struct rq *rq, struct task_struct *p, int sd_flag, int wake_
        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;
 
@@ -1490,13 +1490,15 @@ select_task_rq_fair(struct rq *rq, struct task_struct *p, int sd_flag, int wake_
                         * 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;
                        }
@@ -1512,6 +1514,7 @@ select_task_rq_fair(struct rq *rq, struct task_struct *p, int sd_flag, int wake_
                        sd = tmp;
        }
 
+#ifdef CONFIG_FAIR_GROUP_SCHED
        if (sched_feat(LB_SHARES_UPDATE)) {
                /*
                 * Pick the largest domain to update shares over
@@ -1528,9 +1531,12 @@ select_task_rq_fair(struct rq *rq, struct task_struct *p, int sd_flag, int wake_
                        spin_lock(&rq->lock);
                }
        }
+#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;