[patch] use cheaper elv_queue_empty when unplug a device

[Chen, Kenneth W]

This patch was posted last year and if I remember correctly, Jens said
he is OK with the patch.  In function __generic_unplug_deivce(), kernel
can use a cheaper function elv_queue_empty() instead of more expensive
elv_next_request to find whether the queue is empty or not. blk_run_queue
can also made conditional on whether queue's emptiness before calling
request_fn().


Signed-off-by: Ken Chen <kenneth.w.chen@xxxxxxxxx>


--- linux-2.6.11/drivers/block/ll_rw_blk.c.orig	2005-03-28 18:22:26.000000000 -0800
+++ linux-2.6.11/drivers/block/ll_rw_blk.c	2005-03-28 18:44:46.000000000 -0800
@@ -1459,7 +1459,7 @@ void __generic_unplug_device(request_que
 	/*
 	 * was plugged, fire request_fn if queue has stuff to do
 	 */
-	if (elv_next_request(q))
+	if (!elv_queue_empty(q))
 		q->request_fn(q);
 }
 EXPORT_SYMBOL(__generic_unplug_device);
@@ -1589,7 +1589,8 @@ void blk_run_queue(struct request_queue

 	spin_lock_irqsave(q->queue_lock, flags);
 	blk_remove_plug(q);
-	q->request_fn(q);
+	if (!elv_queue_empty(q))
+		q->request_fn(q);
 	spin_unlock_irqrestore(q->queue_lock, flags);
 }
 EXPORT_SYMBOL(blk_run_queue);




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