On Mon, 2017-03-13 at 09:48 -0600, Christoph Hellwig wrote:
> @@ -1534,7 +1529,36 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
> }
>
> plug = current->plug;
> - if (((plug && !blk_queue_nomerges(q)) || is_sync)) {
> + if (plug && q->nr_hw_queues == 1) {
> + struct request *last = NULL;
> +
> + blk_mq_bio_to_request(rq, bio);
> +
> + /*
> + * @request_count may become stale because of schedule
> + * out, so check the list again.
> + */
The above comment was relevant as long as there was a request_count assignment
above blk_mq_sched_get_request(). This patch moves that assignment inside if
(plug && q->nr_hw_queues == 1). Does that mean that the above comment should be
removed entirely?
> + if (list_empty(&plug->mq_list))
> + request_count = 0;
> + else if (blk_queue_nomerges(q))
> + request_count = blk_plug_queued_count(q);
> +
> + if (!request_count)
> + trace_block_plug(q);
> + else
> + last = list_entry_rq(plug->mq_list.prev);
> +
> + blk_mq_put_ctx(data.ctx);
> +
> + if (request_count >= BLK_MAX_REQUEST_COUNT || (last &&
> + blk_rq_bytes(last) >= BLK_PLUG_FLUSH_SIZE)) {
> + blk_flush_plug_list(plug, false);
> + trace_block_plug(q);
> + }
> +
> + list_add_tail(&rq->queuelist, &plug->mq_list);
> + goto done;
> + } else if (((plug && !blk_queue_nomerges(q)) || is_sync)) {
> struct request *old_rq = NULL;
>
> blk_mq_bio_to_request(rq, bio);
Bart.
