From: Ken Chen 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 Signed-off-by: Ken Chen Signed-off-by: Andrew Morton --- 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 2005-04-07 18:33:11.000000000 -0700 +++ 25-akpm/drivers/block/ll_rw_blk.c 2005-04-07 18:33:11.000000000 -0700 @@ -1586,7 +1586,8 @@ 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); _