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>

1 files changed, 3 insertions, 11 deletions

diff --git a/block/deadline-iosched.c b/block/deadline-iosched.c
index 342448c3d2d..07b80e4642f 100644
--- 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