If we have that hook, we know the driver handles bd->last == true in
a smart fashion. If it does, even for multiple hardware queues, it's
a good idea to flush batches of requests to the device, if we have
batches of requests from the submitter.
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
---
block/blk-mq.c | 26 ++++++++++++++++++++++++++
1 file changed, 26 insertions(+)
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 0a12cec0b426..232f4914c8db 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1953,6 +1953,32 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
list_add_tail(&rq->queuelist, &plug->mq_list);
plug->rq_count++;
plug->do_sort = true;
+ } else if (plug && q->mq_ops->commit_rqs) {
+ /*
+ * If we have a ->commit_rqs(), then we know the driver can
+ * batch submission doorbell updates. Add rq to plug list,
+ * and flush if we exceed the plug count only.
+ */
+ blk_mq_bio_to_request(rq, bio);
+ blk_mq_put_ctx(data.ctx);
+
+ /*
+ * If we have requests for more than one queue here, we
+ * should sort the list when it's flushed.
+ */
+ if (!plug->do_sort && !list_empty(&plug->mq_list)) {
+ same_queue_rq = list_first_entry(&plug->mq_list,
+ struct request, queuelist);
+ if (same_queue_rq->q != q)
+ plug->do_sort = true;
+ }
+
+ list_add_tail(&rq->queuelist, &plug->mq_list);
+ plug->rq_count++;
+ if (plug->rq_count >= BLK_MAX_REQUEST_COUNT) {
+ blk_flush_plug_list(plug, false);
+ trace_block_plug(q);
+ }
} else if (plug && !blk_queue_nomerges(q)) {
blk_mq_bio_to_request(rq, bio);
--
2.17.1
