[PATCH V4 12/16] blokc: mq-deadline: Introduce dispatch helpers

[Damien Le Moal]

Avoid directly referencing the next_rq and fifo_list arrays using the
helper functions deadline_next_request() and deadline_fifo_request() to
facilitate changes in the dispatch request selection in
__dd_dispatch_request().

Signed-off-by: Damien Le Moal <damien.lem...@wdc.com>
---
 block/mq-deadline.c | 39 +++++++++++++++++++++++++++++++--------
 1 file changed, 31 insertions(+), 8 deletions(-)

diff --git a/block/mq-deadline.c b/block/mq-deadline.c
index fb88fee0fb54..1236a464b547 100644
--- a/block/mq-deadline.c
+++ b/block/mq-deadline.c
@@ -196,13 +196,36 @@ static inline int deadline_check_fifo(struct 
deadline_data *dd, int ddir)
 }
 
 /*
+ * For the specified data direction, return the next request to
+ * dispatch using arrival ordered lists.
+ */
+static struct request *
+deadline_fifo_request(struct deadline_data *dd, int data_dir)
+{
+       if (list_empty(&dd->fifo_list[data_dir]))
+               return NULL;
+
+       return rq_entry_fifo(dd->fifo_list[data_dir].next);
+}
+
+/*
+ * For the specified data direction, return the next request to
+ * dispatch using sector position sorted lists.
+ */
+static struct request *
+deadline_next_request(struct deadline_data *dd, int data_dir)
+{
+       return dd->next_rq[data_dir];
+}
+
+/*
  * deadline_dispatch_requests selects the best request according to
  * read/write expire, fifo_batch, etc
  */
 static struct request *__dd_dispatch_request(struct blk_mq_hw_ctx *hctx)
 {
        struct deadline_data *dd = hctx->queue->elevator->elevator_data;
-       struct request *rq;
+       struct request *rq, *next_rq;
        bool reads, writes;
        int data_dir;
 
@@ -218,10 +241,9 @@ static struct request *__dd_dispatch_request(struct 
blk_mq_hw_ctx *hctx)
        /*
         * batches are currently reads XOR writes
         */
-       if (dd->next_rq[WRITE])
-               rq = dd->next_rq[WRITE];
-       else
-               rq = dd->next_rq[READ];
+       rq = deadline_next_request(dd, WRITE);
+       if (!rq)
+               rq = deadline_next_request(dd, READ);
 
        if (rq && dd->batching < dd->fifo_batch)
                /* we have a next request are still entitled to batch */
@@ -264,19 +286,20 @@ static struct request *__dd_dispatch_request(struct 
blk_mq_hw_ctx *hctx)
        /*
         * we are not running a batch, find best request for selected data_dir
         */
-       if (deadline_check_fifo(dd, data_dir) || !dd->next_rq[data_dir]) {
+       next_rq = deadline_next_request(dd, data_dir);
+       if (deadline_check_fifo(dd, data_dir) || !next_rq) {
                /*
                 * A deadline has expired, the last request was in the other
                 * direction, or we have run out of higher-sectored requests.
                 * Start again from the request with the earliest expiry time.
                 */
-               rq = rq_entry_fifo(dd->fifo_list[data_dir].next);
+               rq = deadline_fifo_request(dd, data_dir);
        } else {
                /*
                 * The last req was the same dir and we have a next request in
                 * sort order. No expired requests so continue on from here.
                 */
-               rq = dd->next_rq[data_dir];
+               rq = next_rq;
        }
 
        dd->batching = 0;
-- 
2.13.5