[2.6.16-mm1 patch] throttling tree patches

[Mike Galbraith <efault@gmx.de>]

Greetings,

I've broken down my throttling tree into 6 patches, which I'll send as
replies to this start-point.

Patch 1/6

Ignore timewarps caused by SMP timestamp rounding.  Also, don't stamp a
task with a computed timestamp, stamp with the already called clock.

Signed-off-by: Mike Galbraith <efault@gmx.de>

--- linux-2.6.16-mm1/kernel/sched.c.org	2006-03-23 15:01:41.000000000 +0100
+++ linux-2.6.16-mm1/kernel/sched.c	2006-03-23 15:02:25.000000000 +0100
@@ -805,6 +805,16 @@
 	unsigned long long __sleep_time = now - p->timestamp;
 	unsigned long sleep_time;
 
+	/*
+	 * On SMP systems, a task can go to sleep on one CPU and
+	 * wake up on another.  When this happens, the timestamp
+	 * is rounded to the nearest tick, which can lead to now
+	 * being less than p->timestamp for short sleeps. Ignore
+	 * these, they're insignificant.
+	 */
+	if (unlikely(now < p->timestamp))
+		__sleep_time = 0ULL;
+
 	if (batch_task(p))
 		sleep_time = 0;
 	else {
@@ -871,20 +881,20 @@
  */
 static void activate_task(task_t *p, runqueue_t *rq, int local)
 {
-	unsigned long long now;
+	unsigned long long now, comp;
 
-	now = sched_clock();
+	now = comp = sched_clock();
 #ifdef CONFIG_SMP
 	if (!local) {
 		/* Compensate for drifting sched_clock */
 		runqueue_t *this_rq = this_rq();
-		now = (now - this_rq->timestamp_last_tick)
+		comp = (now - this_rq->timestamp_last_tick)
 			+ rq->timestamp_last_tick;
 	}
 #endif
 
 	if (!rt_task(p))
-		p->prio = recalc_task_prio(p, now);
+		p->prio = recalc_task_prio(p, comp);
 
 	/*
 	 * This checks to make sure it's not an uninterruptible task