[patch 128/198] use cheaper elv_queue_empty when unplug a device

[akpm]

From: Ken Chen <kenneth.w.chen@xxxxxxxxx>

In function __generic_unplug_device(), 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: Jens Axboe <axboe@xxxxxxx>
Signed-off-by: Ken Chen <kenneth.w.chen@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
---

 25-akpm/drivers/block/ll_rw_blk.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletion(-)

diff -puN drivers/block/ll_rw_blk.c~use-cheaper-elv_queue_empty-when-unplug-a-device drivers/block/ll_rw_blk.c
--- 25/drivers/block/ll_rw_blk.c~use-cheaper-elv_queue_empty-when-unplug-a-device	2005-04-12 03:21:34.394908080 -0700
+++ 25-akpm/drivers/block/ll_rw_blk.c	2005-04-12 03:21:34.399907320 -0700
@@ -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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