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: d62cbcf62f2f ("nvme: add support for mq_ops->queue_rqs()")
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
---
drivers/nvme/host/pci.c | 39 +++++++++++++++++----------------------
1 file changed, 17 insertions(+), 22 deletions(-)
diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index 4b9fda0b1d9a..c66ea2c23690 100644
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -904,9 +904,10 @@ 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);
@@ -931,31 +932,25 @@ 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;
}
--
2.45.2
