[PATCH] sched: consider migration thread with smp nice

The intermittent scheduling of the migration thread at ultra high priority
makes the smp nice handling see that runqueue as being heavily loaded.  The
migration thread itself actually handles the balancing so its influence on
priority balancing should be ignored.

Signed-off-by: Con Kolivas <kernel@kolivas.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/kernel/sched.c b/kernel/sched.c
index 502d47c883b6a2f271b027351195816b961ae1a4..0f2def822296cae1dfc2eb9710b6b05e3c07a3d9 100644 (file)
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -670,6 +670,31 @@ static inline void dec_prio_bias(runqueue_t *rq, int prio)
 {
        rq->prio_bias -= MAX_PRIO - prio;
 }
+
+static inline void inc_nr_running(task_t *p, runqueue_t *rq)
+{
+       rq->nr_running++;
+       if (rt_task(p)) {
+               if (p != rq->migration_thread)
+                       /*
+                        * The migration thread does the actual balancing. Do
+                        * not bias by its priority as the ultra high priority
+                        * will skew balancing adversely.
+                        */
+                       inc_prio_bias(rq, p->prio);
+       } else
+               inc_prio_bias(rq, p->static_prio);
+}
+
+static inline void dec_nr_running(task_t *p, runqueue_t *rq)
+{
+       rq->nr_running--;
+       if (rt_task(p)) {
+               if (p != rq->migration_thread)
+                       dec_prio_bias(rq, p->prio);
+       } else
+               dec_prio_bias(rq, p->static_prio);
+}
 #else
 static inline void inc_prio_bias(runqueue_t *rq, int prio)
 {
@@ -678,25 +703,17 @@ static inline void inc_prio_bias(runqueue_t *rq, int prio)
 static inline void dec_prio_bias(runqueue_t *rq, int prio)
 {
 }
-#endif
 
 static inline void inc_nr_running(task_t *p, runqueue_t *rq)
 {
        rq->nr_running++;
-       if (rt_task(p))
-               inc_prio_bias(rq, p->prio);
-       else
-               inc_prio_bias(rq, p->static_prio);
 }
 
 static inline void dec_nr_running(task_t *p, runqueue_t *rq)
 {
        rq->nr_running--;
-       if (rt_task(p))
-               dec_prio_bias(rq, p->prio);
-       else
-               dec_prio_bias(rq, p->static_prio);
 }
+#endif
 
 /*
  * __activate_task - move a task to the runqueue.