deadline-iosched: allow non-sequential batching

Deadline currently only batches sector-contiguous requests, so except
for a few circumstances (e.g. requests in a single direction), it is
essentially first come first served.  This is bad for throughput, so
change it to CSCAN, which means requests in a batch do not need to be
sequential and are issued in increasing sector order.

Signed-off-by: Aaron Carroll <aaronc@gelato.unsw.edu.au>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

diff --git a/block/deadline-iosched.c b/block/deadline-iosched.c
index 342448c..07b80e4 100644 (file)
--- a/block/deadline-iosched.c
+++ b/block/deadline-iosched.c
@@ -258,17 +258,9 @@ static int deadline_dispatch_requests(struct request_queue *q, int force)
        else
                rq = dd->next_rq[READ];
 
-       if (rq) {
-               /* we have a "next request" */
-               
-               if (dd->last_sector != rq->sector)
-                       /* end the batch on a non sequential request */
-                       dd->batching += dd->fifo_batch;
-               
-               if (dd->batching < dd->fifo_batch)
-                       /* we are still entitled to batch */
-                       goto dispatch_request;
-       }
+       if (rq && dd->batching < dd->fifo_batch)
+               /* we have a next request are still entitled to batch */
+               goto dispatch_request;
 
        /*
         * at this point we are not running a batch. select the appropriate