sched: Fix schedstat.nr_wakeups_migrate

While looking over the code I found that with the ttwu rework the
nr_wakeups_migrate test broke since we now switch cpus prior to
calling ttwu_stat(), hence the test is always true.

Cure this by passing the migration state in wake_flags. Also move the
whole test under CONFIG_SMP, its hard to migrate tasks on UP :-)

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/n/tip-pwwxl7gdqs5676f1d4cx6pj7@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 8 insertions, 4 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 8da84b7bc1b8..483c1ed5bc4d 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1063,6 +1063,7 @@ struct sched_domain;
  */
 #define WF_SYNC         0x01            /* waker goes to sleep after wakup */
 #define WF_FORK         0x02            /* child wakeup after fork */
+#define WF_MIGRATED     0x04            /* internal use, task got migrated */
 
 #define ENQUEUE_WAKEUP          1
 #define ENQUEUE_HEAD            2
diff --git a/kernel/sched.c b/kernel/sched.c
index 49cc70b152cf..2fe98ed474da 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -2447,6 +2447,10 @@ ttwu_stat(struct task_struct *p, int cpu, int wake_flags)
                 }
                 rcu_read_unlock();
         }
+
+        if (wake_flags & WF_MIGRATED)
+                schedstat_inc(p, se.statistics.nr_wakeups_migrate);
+
 #endif /* CONFIG_SMP */
 
         schedstat_inc(rq, ttwu_count);
@@ -2455,9 +2459,6 @@ ttwu_stat(struct task_struct *p, int cpu, int wake_flags)
         if (wake_flags & WF_SYNC)
                 schedstat_inc(p, se.statistics.nr_wakeups_sync);
 
-        if (cpu != task_cpu(p))
-                schedstat_inc(p, se.statistics.nr_wakeups_migrate);
-
 #endif /* CONFIG_SCHEDSTATS */
 }
 
@@ -2675,8 +2676,10 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
                 p->sched_class->task_waking(p);
 
         cpu = select_task_rq(p, SD_BALANCE_WAKE, wake_flags);
-        if (task_cpu(p) != cpu)
+        if (task_cpu(p) != cpu) {
+                wake_flags |= WF_MIGRATED;
                 set_task_cpu(p, cpu);
+        }
 #endif /* CONFIG_SMP */
 
         ttwu_queue(p, cpu);