[PATCH 1/5] 2.6.0 fix preempt ctx switch accounting

[Nick Piggin]

Make sure to count kernel preemption as a context switch. A short cut
has been preventing it.



Make sure to count kernel preemption as a context switch. A short cut
has been preventing it.


 linux-2.6-npiggin/kernel/sched.c |   37 +++++++++++++++----------------------
 1 files changed, 15 insertions(+), 22 deletions(-)

diff -puN kernel/sched.c~sched-ctx-count-preempt kernel/sched.c
--- linux-2.6/kernel/sched.c~sched-ctx-count-preempt	2003-12-04 13:01:03.000000000 +1100
+++ linux-2.6-npiggin/kernel/sched.c	2003-12-04 13:01:26.000000000 +1100
@@ -1512,33 +1512,20 @@ need_resched:
 
 	spin_lock_irq(&rq->lock);
 
-	/*
-	 * if entering off of a kernel preemption go straight
-	 * to picking the next task.
-	 */
-	if (unlikely(preempt_count() & PREEMPT_ACTIVE))
-		goto pick_next_task;
-
-	switch (prev->state) {
-	case TASK_INTERRUPTIBLE:
-		if (unlikely(signal_pending(prev))) {
+	if (prev->state != TASK_RUNNING &&
+			likely(!(preempt_count() & PREEMPT_ACTIVE)) ) {
+		if (unlikely(signal_pending(prev)) &&
+				prev->state == TASK_INTERRUPTIBLE)
 			prev->state = TASK_RUNNING;
-			break;
-		}
-	default:
-		deactivate_task(prev, rq);
-		prev->nvcsw++;
-		break;
-	case TASK_RUNNING:
-		prev->nivcsw++;
+		else
+			deactivate_task(prev, rq);
 	}
-pick_next_task:
-	if (unlikely(!rq->nr_running)) {
+
 #ifdef CONFIG_SMP
+	if (unlikely(!rq->nr_running))
 		load_balance(rq, 1, cpu_to_node_mask(smp_processor_id()));
-		if (rq->nr_running)
-			goto pick_next_task;
 #endif
+	if (unlikely(!rq->nr_running)) {
 		next = rq->idle;
 		rq->expired_timestamp = 0;
 		goto switch_tasks;
@@ -1585,6 +1572,12 @@ switch_tasks:
 	prev->timestamp = now;
 
 	if (likely(prev != next)) {
+		if (prev->state == TASK_RUNNING ||
+				unlikely(preempt_count() & PREEMPT_ACTIVE))
+			prev->nivcsw++;
+		else
+			prev->nvcsw++;
+
 		next->timestamp = now;
 		rq->nr_switches++;
 		rq->curr = next;

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