[PATCH] sched: optimize activate_task for RT task

RT task does not participate in interactiveness priority and thus shouldn't
be bothered with timestamp and p->sleep_type manipulation when task is
being put on run queue.  Bypass all of the them with a single if (rt_task)
test.

Signed-off-by: Ken Chen <kenneth.w.chen@intel.com>
Acked-by: Ingo Molnar <mingo@elte.hu>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: "Siddha, Suresh B" <suresh.b.siddha@intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 5 insertions, 3 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index 66e44b5b53d2..48e35c916326 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -940,6 +940,9 @@ static void activate_task(struct task_struct *p, struct rq *rq, int local)
 {
         unsigned long long now;
 
+        if (rt_task(p))
+                goto out;
+
         now = sched_clock();
 #ifdef CONFIG_SMP
         if (!local) {
@@ -961,8 +964,7 @@ static void activate_task(struct task_struct *p, struct rq *rq, int local)
                                      (now - p->timestamp) >> 20);
         }
 
-        if (!rt_task(p))
-                p->prio = recalc_task_prio(p, now);
+        p->prio = recalc_task_prio(p, now);
 
         /*
          * This checks to make sure it's not an uninterruptible task
@@ -987,7 +989,7 @@ static void activate_task(struct task_struct *p, struct rq *rq, int local)
                 }
         }
         p->timestamp = now;
-
+out:
         __activate_task(p, rq);
 }