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>

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index e4d4483..a32df15 100644 (file)
--- 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;
                        }
                }