[PATCH] sched: dont decrease idle sleep avg

We watch for tasks that sleep extended periods and don't allow one single
prolonged sleep period from elevating priority to maximum bonus to prevent cpu
bound tasks from getting high priority with single long sleeps.  There is a
bug in the current code that also penalises tasks that already have high
priority.  Correct that bug.

Signed-off-by: Con Kolivas <kernel@kolivas.org>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

kernel/sched.c

@@ -700,14 +700,19 @@ static int recalc_task_prio(task_t *p, unsigned long long now)
 	if (likely(sleep_time > 0)) {
 		/*
 		 * User tasks that sleep a long time are categorised as
-		 * idle and will get just interactive status to stay active &
-		 * prevent them suddenly becoming cpu hogs and starving
-		 * other processes.
+		 * idle. They will only have their sleep_avg increased to a
+		 * level that makes them just interactive priority to stay
+		 * active yet prevent them suddenly becoming cpu hogs and
+		 * starving other processes.
 		 */
 		if (p->mm && p->sleep_type != SLEEP_NONINTERACTIVE &&
 			sleep_time > INTERACTIVE_SLEEP(p)) {
-				p->sleep_avg = JIFFIES_TO_NS(MAX_SLEEP_AVG -
-						DEF_TIMESLICE);
+				unsigned long ceiling;
+
+				ceiling = JIFFIES_TO_NS(MAX_SLEEP_AVG -
+					DEF_TIMESLICE);
+				if (p->sleep_avg < ceiling)
+					p->sleep_avg = ceiling;
 		} else {
 			/*
 			 * Tasks waking from uninterruptible sleep are