sched: Cleanup select_task_rq_fair()

Clean up the new affine to idle sibling bits while trying to
grok them. Should not have any function differences.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
LKML-Reference: <20091112145610.832503781@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 51 insertions, 22 deletions

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index e4d4483fd617..a32df1524746 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1319,6 +1319,41 @@ 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) {
+                if (!cpu_rq(prev_cpu)->cfs.nr_running)
+                        target = prev_cpu;
+        }
+
+        /*
+         * Otherwise, iterate the domain and find an elegible idle cpu.
+         */
+        if (target == -1 || target == 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.
@@ -1373,36 +1408,30 @@ static int select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flag
                 }
 
                 if (want_affine && (tmp->flags & SD_WAKE_AFFINE)) {
-                        int candidate = -1, i;
+                        int target = -1;
 
+                        /*
+                         * 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)))
-                                candidate = cpu;
+                                target = cpu;
 
                         /*
-                         * Check for an idle shared cache.
+                         * If there's an idle sibling in this domain, make that
+                         * the wake_affine target instead of the current cpu.
+                         *
+                         * XXX: should we possibly do this outside of
+                         * WAKE_AFFINE, in case the shared cache domain is
+                         * smaller than the WAKE_AFFINE domain?
                          */
-                        if (tmp->flags & SD_PREFER_SIBLING) {
-                                if (candidate == cpu) {
-                                        if (!cpu_rq(prev_cpu)->cfs.nr_running)
-                                                candidate = prev_cpu;
-                                }
-
-                                if (candidate == -1 || candidate == cpu) {
-                                        for_each_cpu(i, sched_domain_span(tmp)) {
-                                                if (!cpumask_test_cpu(i, &p->cpus_allowed))
-                                                        continue;
-                                                if (!cpu_rq(i)->cfs.nr_running) {
-                                                        candidate = i;
-                                                        break;
-                                                }
-                                        }
-                                }
-                        }
+                        if (tmp->flags & SD_PREFER_SIBLING)
+                                target = select_idle_sibling(p, tmp, target);
 
-                        if (candidate >= 0) {
+                        if (target >= 0) {
                                 affine_sd = tmp;
                                 want_affine = 0;
-                                cpu = candidate;
+                                cpu = target;
                         }
                 }