[patch] sched: optimize activate_task for RT task

[patch] sched: optimize activate_task for RT task

[Chen, Kenneth W]

RT task does not participate in interactiveness priority and thus
shouldn't be bothered with timestamp when task is being put on run
queue. We should push all of the time calculation inside already
existed if (!rt_task) block.


Signed-off-by: Ken Chen <kenneth.w.chen@intel.com>

--- ./kernel/sched.c.orig	2006-11-14 13:29:37.000000000 -0800
+++ ./kernel/sched.c	2006-11-14 13:52:02.000000000 -0800
@@ -936,20 +936,19 @@ static int recalc_task_prio(struct task_
  */
 static void activate_task(struct task_struct *p, struct rq *rq, int local)
 {
-	unsigned long long now;
-
-	now = sched_clock();
+	if (!rt_task(p)) {
+		unsigned long long now = sched_clock();
 #ifdef CONFIG_SMP
-	if (!local) {
-		/* Compensate for drifting sched_clock */
-		struct rq *this_rq = this_rq();
-		now = (now - this_rq->timestamp_last_tick)
-			+ rq->timestamp_last_tick;
-	}
+		if (!local) {
+			/* Compensate for drifting sched_clock */
+			struct rq *this_rq = this_rq();
+			now = (now - this_rq->timestamp_last_tick)
+				+ rq->timestamp_last_tick;
+		}
 #endif
-
-	if (!rt_task(p))
 		p->prio = recalc_task_prio(p, now);
+		p->timestamp = now;
+	}
 
 	/*
 	 * This checks to make sure it's not an uninterruptible task
@@ -973,7 +972,6 @@ static void activate_task(struct task_st
 			p->sleep_type = SLEEP_INTERACTIVE;
 		}
 	}
-	p->timestamp = now;
 
 	__activate_task(p, rq);
 }