[2.6.16-mm1 patch] ignore timewarps

[Mike Galbraith <efault@gmx.de>]

Greetings,

The patch below is a correction to patch 1 of my throttling tree series.

The only thing that really matters is that timewarps are ignored,
whatever the cause.  This patch does that, and only that.

	-Mike

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 +805,15 @@
 	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, now can
+	 * end up being less than p->timestamp for short sleeps.
+	 * Ignore these, they're insignificant.
+	 */
+	if (unlikely(now < p->timestamp))
+		__sleep_time = 0;
+
 	if (batch_task(p))
 		sleep_time = 0;
 	else {