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 <[email protected]> --- 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
