[PATCH] optimize activate_task()

recalc_task_prio() is called from activate_task() to calculate dynamic
priority and interactive credit for the activating task.  For real-time
scheduling process, all that dynamic calculation is thrown away at the end
because rt priority is fixed.  Patch to optimize recalc_task_prio() away
for rt processes.

Signed-off-by: Ken Chen <kenneth.w.chen@intel.com>
Acked-by: Ingo Molnar <mingo@elte.hu>
Cc: Nick Piggin <piggin@cyberone.com.au>
Cc: Con Kolivas <kernel@kolivas.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

kernel/sched.c

@@ -815,7 +815,8 @@ static void activate_task(task_t *p, runqueue_t *rq, int local)
 	}
 #endif
 
-	p->prio = recalc_task_prio(p, now);
+	if (!rt_task(p))
+		p->prio = recalc_task_prio(p, now);
 
 	/*
 	 * This checks to make sure it's not an uninterruptible task