[PATCH 3/4] workqueue: Use mod_timer for queue_delayed_work()

[Peter Zijlstra <a.p.zijlstra@chello.nl>]

[-- Attachment #1: workqueue-mod_timer_on.patch --]
[-- Type: text/plain, Size: 1240 bytes --]

Use mod_timer for queue_delayed_work(), this allows us to avoid
calling cancel_delayed_work() prior to calling queue_delayed_work()
when changing a work's expiration time.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
---
Index: linux-2.6/kernel/workqueue.c
===================================================================
--- linux-2.6.orig/kernel/workqueue.c
+++ linux-2.6/kernel/workqueue.c
@@ -1107,8 +1107,15 @@ static void delayed_work_timer_fn(unsign
 int queue_delayed_work(struct workqueue_struct *wq,
 			struct delayed_work *dwork, unsigned long delay)
 {
-	if (delay == 0)
+	if (delay == 0) {
+		/*
+		 * If the timer callback is currently running the work
+		 * is already being enqueued and we don't actually have
+		 * to do anything to make it run now...
+		 */
+		__cancel_delayed_work(dwork);
 		return queue_work(wq, &dwork->work);
+	}
 
 	return queue_delayed_work_on(-1, wq, dwork, delay);
 }
@@ -1160,9 +1167,9 @@ int queue_delayed_work_on(int cpu, struc
 		timer->function = delayed_work_timer_fn;
 
 		if (unlikely(cpu >= 0))
-			add_timer_on(timer, cpu);
+			mod_timer_on(timer, cpu);
 		else
-			add_timer(timer);
+			mod_timer(timer);
 		ret = 1;
 	}
 	return ret;