[patch] use cheaper elv_queue_empty when unplug a device

Chen, Kenneth W
2005-03-29T02:54:02Z

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@intel.com>

--- 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);