[PATCH 1/4] block: add mq_ops->queue_rqs hook

Jens Axboe
2021-12-16T16:06:33Z

If we have a list of requests in our plug list, send it to the driver in
one go, if possible. The driver must set mq_ops->queue_rqs() to support
this, if not the usual one-by-one path is used.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
block/blk-mq.c | 26 +++++++++++++++++++++++---
include/linux/blk-mq.h | 8 ++++++++
2 files changed, 31 insertions(+), 3 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 75154cc788db..51991232824a 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2553,6 +2553,7 @@ void blk_mq_flush_plug_list(struct blk_plug *plug, bool from_schedule)
{
struct blk_mq_hw_ctx *this_hctx;
struct blk_mq_ctx *this_ctx;
+ struct request *rq;
unsigned int depth;
LIST_HEAD(list);

@@ -2561,7 +2562,28 @@ void blk_mq_flush_plug_list(struct blk_plug *plug, bool from_schedule)
plug->rq_count = 0;

if (!plug->multiple_queues && !plug->has_elevator && !from_schedule) {
- struct request_queue *q = rq_list_peek(&plug->mq_list)->q;
+ struct request_queue *q;
+
+ rq = rq_list_peek(&plug->mq_list);
+ q = rq->q;
+
+ /*
+ * Peek first request and see if we have a ->queue_rqs() hook.
+ * If we do, we can dispatch the whole plug list in one go. We
+ * already know at this point that all requests belong to the
+ * same queue, caller must ensure that's the case.
+ *
+ * Since we pass off the full list to the driver at this point,
+ * we do not increment the active request count for the queue.
+ * Bypass shared tags for now because of that.
+ */
+ if (q->mq_ops->queue_rqs &&
+ !(rq->mq_hctx->flags & BLK_MQ_F_TAG_QUEUE_SHARED)) {
+ blk_mq_run_dispatch_ops(q,
+ q->mq_ops->queue_rqs(&plug->mq_list));
+ if (rq_list_empty(plug->mq_list))
+ return;
+ }

blk_mq_run_dispatch_ops(q,
blk_mq_plug_issue_direct(plug, false));
@@ -2573,8 +2595,6 @@ void blk_mq_flush_plug_list(struct blk_plug *plug, bool from_schedule)
this_ctx = NULL;
depth = 0;
do {
- struct request *rq;
-
rq = rq_list_pop(&plug->mq_list);

if (!this_hctx) {
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index 772f8f921526..550996cf419c 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -492,6 +492,14 @@ struct blk_mq_ops {
*/
void (*commit_rqs)(struct blk_mq_hw_ctx *);

+ /**
+ * @queue_rqs: Queue a list of new requests. Driver is guaranteed
+ * that each request belongs to the same queue. If the driver doesn't
+ * empty the @rqlist completely, then the rest will be queued
+ * individually by the block layer upon return.
+ */
+ void (*queue_rqs)(struct request **rqlist);
+
/**
* @get_budget: Reserve budget before queue request, once .queue_rq is
* run, it is driver's responsibility to release the
--
2.34.1