[PATCH 2.6.21-rc6] sched: modification of TASK_PREEMPTS_CURRENT to avoid redundant reschedules (e.g. in set_user_nice)

[Dmitry Adamushko]

From: Dmitry Adamushko <dmitry.adamushko@xxxxxxxxx>

o  Fixed a mail client (shouldn't be white-space damaged now);
o  Andrew, a patch against SD will follow.

---

o  Make TASK_PREEMPTS_CURR(task, rq) return "true" only if the task's
prio is higher than the current's one and the task is in the "active"
array.
This ensures we don't make redundant resched_task() calls when the
task is in the "expired" array (as may happen now in set_user_prio(),
rt_mutex_setprio() and pull_task() ) ;

o  generilise conditions for a call to resched_task() in
set_user_nice(), rt_mutex_setprio() and sched_setscheduler()


Signed-off-by: Dmitry Adamushko <dmitry.adamushko@xxxxxxxxx>

---

--- linux-2.6.21-rc6/kernel/sched-orig.c	2007-04-07 17:16:16.000000000 +0200
+++ linux-2.6.21-rc6/kernel/sched.c	2007-04-07 18:13:49.000000000 +0200
@@ -168,7 +168,7 @@ unsigned long long __attribute__((weak))
 		(MAX_BONUS / 2 + DELTA((p)) + 1) / MAX_BONUS - 1))
 
 #define TASK_PREEMPTS_CURR(p, rq) \
-	((p)->prio < (rq)->curr->prio)
+	(((p)->prio < (rq)->curr->prio) && ((p)->array == (rq)->active))
 
 #define SCALE_PRIO(x, prio) \
 	max(x * (MAX_PRIO - prio) / (MAX_USER_PRIO / 2), MIN_TIMESLICE)
@@ -3847,13 +3847,13 @@ void rt_mutex_setprio(struct task_struct
 	struct prio_array *array;
 	unsigned long flags;
 	struct rq *rq;
-	int oldprio;
+	int delta;
 
 	BUG_ON(prio < 0 || prio > MAX_PRIO);
 
 	rq = task_rq_lock(p, &flags);
 
-	oldprio = p->prio;
+	delta = prio - p->prio;
 	array = p->array;
 	if (array)
 		dequeue_task(p, array);
@@ -3869,13 +3869,11 @@ void rt_mutex_setprio(struct task_struct
 		enqueue_task(p, array);
 		/*
 		 * Reschedule if we are currently running on this runqueue and
-		 * our priority decreased, or if we are not currently running on
-		 * this runqueue and our priority is higher than the current's
+		 * our priority decreased, or if our priority became higher
+		 * than the current's.
 		 */
-		if (task_running(rq, p)) {
-			if (p->prio > oldprio)
-				resched_task(rq->curr);
-		} else if (TASK_PREEMPTS_CURR(p, rq))
+		if (TASK_PREEMPTS_CURR(p, rq) ||
+				(delta > 0 && task_running(rq, p)))
 			resched_task(rq->curr);
 	}
 	task_rq_unlock(rq, &flags);
@@ -3923,10 +3921,12 @@ void set_user_nice(struct task_struct *p
 		enqueue_task(p, array);
 		inc_raw_weighted_load(rq, p);
 		/*
-		 * If the task increased its priority or is running and
-		 * lowered its priority, then reschedule its CPU:
+		 * Reschedule if we are currently running on this runqueue and
+		 * our priority decreased, or if our priority became higher
+		 * than the current's.
 		 */
-		if (delta < 0 || (delta > 0 && task_running(rq, p)))
+		if (TASK_PREEMPTS_CURR(p, rq) ||
+				(delta > 0 && task_running(rq, p)))
 			resched_task(rq->curr);
 	}
 out_unlock:
@@ -4153,13 +4153,11 @@ recheck:
 		__activate_task(p, rq);
 		/*
 		 * Reschedule if we are currently running on this runqueue and
-		 * our priority decreased, or if we are not currently running on
-		 * this runqueue and our priority is higher than the current's
+		 * our priority decreased, or our priority became higher
+		 * than the current's.
 		 */
-		if (task_running(rq, p)) {
-			if (p->prio > oldprio)
-				resched_task(rq->curr);
-		} else if (TASK_PREEMPTS_CURR(p, rq))
+		if (TASK_PREEMPTS_CURR(p, rq) ||
+				(task_running(rq, p) && p->prio > oldprio))
 			resched_task(rq->curr);
 	}
 	__task_rq_unlock(rq);
-
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