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    Subject[patch] use cheaper elv_queue_empty when unplug a device
    Date
    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);



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