1 files changed, 60 insertions, 5 deletions

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 37087a7fac22..f61837ad336d 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1345,6 +1345,37 @@ find_idlest_cpu(struct sched_group *group, struct task_struct *p, int this_cpu)
 }
 
 /*
+ * Try and locate an idle CPU in the sched_domain.
+ */
+static int
+select_idle_sibling(struct task_struct *p, struct sched_domain *sd, int target)
+{
+        int cpu = smp_processor_id();
+        int prev_cpu = task_cpu(p);
+        int i;
+
+        /*
+         * If this domain spans both cpu and prev_cpu (see the SD_WAKE_AFFINE
+         * test in select_task_rq_fair) and the prev_cpu is idle then that's
+         * always a better target than the current cpu.
+         */
+        if (target == cpu && !cpu_rq(prev_cpu)->cfs.nr_running)
+                return prev_cpu;
+
+        /*
+         * Otherwise, iterate the domain and find an elegible idle cpu.
+         */
+        for_each_cpu_and(i, sched_domain_span(sd), &p->cpus_allowed) {
+                if (!cpu_rq(i)->cfs.nr_running) {
+                        target = i;
+                        break;
+                }
+        }
+
+        return target;
+}
+
+/*
  * sched_balance_self: balance the current task (running on cpu) in domains
  * that have the 'flag' flag set. In practice, this is SD_BALANCE_FORK and
  * SD_BALANCE_EXEC.
@@ -1398,11 +1429,35 @@ static int select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flag
                                 want_sd = 0;
                 }
 
-                if (want_affine && (tmp->flags & SD_WAKE_AFFINE) &&
-                    cpumask_test_cpu(prev_cpu, sched_domain_span(tmp))) {
+                /*
+                 * While iterating the domains looking for a spanning
+                 * WAKE_AFFINE domain, adjust the affine target to any idle cpu
+                 * in cache sharing domains along the way.
+                 */
+                if (want_affine) {
+                        int target = -1;
 
-                        affine_sd = tmp;
-                        want_affine = 0;
+                        /*
+                         * If both cpu and prev_cpu are part of this domain,
+                         * cpu is a valid SD_WAKE_AFFINE target.
+                         */
+                        if (cpumask_test_cpu(prev_cpu, sched_domain_span(tmp)))
+                                target = cpu;
+
+                        /*
+                         * If there's an idle sibling in this domain, make that
+                         * the wake_affine target instead of the current cpu.
+                         */
+                        if (tmp->flags & SD_PREFER_SIBLING)
+                                target = select_idle_sibling(p, tmp, target);
+
+                        if (target >= 0) {
+                                if (tmp->flags & SD_WAKE_AFFINE) {
+                                        affine_sd = tmp;
+                                        want_affine = 0;
+                                }
+                                cpu = target;
+                        }
                 }
 
                 if (!want_sd && !want_affine)
@@ -1679,7 +1734,7 @@ static struct task_struct *pick_next_task_fair(struct rq *rq)
         struct cfs_rq *cfs_rq = &rq->cfs;
         struct sched_entity *se;
 
-        if (unlikely(!cfs_rq->nr_running))
+        if (!cfs_rq->nr_running)
                 return NULL;
 
         do {