Deadline iosched: Reset batch for ordered requests

The deadline I/O scheduler does not reset the batch count when starting
a new batch at a higher-sectored request.  This means the second and
subsequent batch in the same data direction will never exceed a single
request in size whenever higher-sectored requests are pending.

This patch gives new batches in the same data direction as old ones
their full quota of requests by resetting the batch count.

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 a44437e..cb94c83 100644 (file)
--- a/block/deadline-iosched.c
+++ b/block/deadline-iosched.c
@@ -306,12 +306,11 @@ dispatch_writes:
 dispatch_find_request:
        /*
         * we are not running a batch, find best request for selected data_dir
+        * and start a new batch
         */
        if (deadline_check_fifo(dd, data_dir)) {
                /* An expired request exists - satisfy it */
-               dd->batching = 0;
                rq = rq_entry_fifo(dd->fifo_list[data_dir].next);
-               
        } else if (dd->next_rq[data_dir]) {
                /*
                 * The last req was the same dir and we have a next request in
@@ -325,12 +324,13 @@ dispatch_find_request:
                 * higher-sectored requests. Go back to the lowest sectored
                 * request (1 way elevator) and start a new batch.
                 */
-               dd->batching = 0;
                node = rb_first(&dd->sort_list[data_dir]);
                if (node)
                        rq = rb_entry_rq(node);
        }
 
+       dd->batching = 0;
+
 dispatch_request:
        /*
         * rq is the selected appropriate request.