Commit beadf008 authored by Christoph Hellwig's avatar Christoph Hellwig Committed by Jens Axboe
Browse files

nvme-pci: reverse request order in nvme_queue_rqs 



blk_mq_flush_plug_list submits requests in the reverse order that they
were submitted, which leads to a rather suboptimal I/O pattern especially
in rotational devices.  Fix this by rewriting nvme_queue_rqs so that it
always pops the requests from the passed in request list, and then adds
them to the head of a local submit list.  This actually simplifies the
code a bit as it removes the complicated list splicing, at the cost of
extra updates of the rq_next pointer.  As that should be cache hot
anyway it should be an easy price to pay.

Fixes: d62cbcf6 ("nvme: add support for mq_ops->queue_rqs()")
Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20241113152050.157179-2-hch@lst.de


Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent e559ee02

drivers/nvme/host/pci.c

+17 −22
Original line number Diff line number Diff line
@@ -906,9 +906,10 @@ static blk_status_t nvme_queue_rq(struct blk_mq_hw_ctx *hctx, 


static void nvme_submit_cmds(struct nvme_queue *nvmeq, struct request **rqlist)

{

	struct request *req;



	spin_lock(&nvmeq->sq_lock);

	while (!rq_list_empty(*rqlist)) {

		struct request *req = rq_list_pop(rqlist);

	while ((req = rq_list_pop(rqlist))) {

		struct nvme_iod *iod = blk_mq_rq_to_pdu(req);



		nvme_sq_copy_cmd(nvmeq, &iod->cmd);
@@ -933,31 +934,25 @@ static bool nvme_prep_rq_batch(struct nvme_queue *nvmeq, struct request *req) 


static void nvme_queue_rqs(struct request **rqlist)

{

	struct request *req, *next, *prev = NULL;

	struct request *submit_list = NULL;

	struct request *requeue_list = NULL;

	struct request **requeue_lastp = &requeue_list;

	struct nvme_queue *nvmeq = NULL;

	struct request *req;



	rq_list_for_each_safe(rqlist, req, next) {

		struct nvme_queue *nvmeq = req->mq_hctx->driver_data;



		if (!nvme_prep_rq_batch(nvmeq, req)) {

			/* detach 'req' and add to remainder list */

			rq_list_move(rqlist, &requeue_list, req, prev);



			req = prev;

			if (!req)

				continue;

		}

	while ((req = rq_list_pop(rqlist))) {

		if (nvmeq && nvmeq != req->mq_hctx->driver_data)

			nvme_submit_cmds(nvmeq, &submit_list);

		nvmeq = req->mq_hctx->driver_data;



		if (!next || req->mq_hctx != next->mq_hctx) {

			/* detach rest of list, and submit */

			req->rq_next = NULL;

			nvme_submit_cmds(nvmeq, rqlist);

			*rqlist = next;

			prev = NULL;

		} else

			prev = req;

		if (nvme_prep_rq_batch(nvmeq, req))

			rq_list_add(&submit_list, req); /* reverse order */

		else

			rq_list_add_tail(&requeue_lastp, req);

	}



	if (nvmeq)

		nvme_submit_cmds(nvmeq, &submit_list);

	*rqlist = requeue_list;

}