[PATCH v5 2/6] block: wire-up support for passthrough plugging

Kanchan Joshi
2022-05-11T06:32:20Z

From: Jens Axboe <axboe@kernel.dk>

Add support for plugging in passthrough path. When plugging is enabled, the
requests are added to a plug instead of getting dispatched to the driver.
And when the plug is finished, the whole batch gets dispatched via
->queue_rqs which turns out to be more efficient. Otherwise dispatching
used to happen via ->queue_rq, one request at a time.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
block/blk-mq.c | 73 +++++++++++++++++++++++++++-----------------------
1 file changed, 39 insertions(+), 34 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 84d749511f55..2cf011b57cf9 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2340,6 +2340,40 @@ void __blk_mq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
blk_mq_hctx_mark_pending(hctx, ctx);
}

+/*
+ * Allow 2x BLK_MAX_REQUEST_COUNT requests on plug queue for multiple
+ * queues. This is important for md arrays to benefit from merging
+ * requests.
+ */
+static inline unsigned short blk_plug_max_rq_count(struct blk_plug *plug)
+{
+ if (plug->multiple_queues)
+ return BLK_MAX_REQUEST_COUNT * 2;
+ return BLK_MAX_REQUEST_COUNT;
+}
+
+static void blk_add_rq_to_plug(struct blk_plug *plug, struct request *rq)
+{
+ struct request *last = rq_list_peek(&plug->mq_list);
+
+ if (!plug->rq_count) {
+ trace_block_plug(rq->q);
+ } else if (plug->rq_count >= blk_plug_max_rq_count(plug) ||
+ (!blk_queue_nomerges(rq->q) &&
+ blk_rq_bytes(last) >= BLK_PLUG_FLUSH_SIZE)) {
+ blk_mq_flush_plug_list(plug, false);
+ trace_block_plug(rq->q);
+ }
+
+ if (!plug->multiple_queues && last && last->q != rq->q)
+ plug->multiple_queues = true;
+ if (!plug->has_elevator && (rq->rq_flags & RQF_ELV))
+ plug->has_elevator = true;
+ rq->rq_next = NULL;
+ rq_list_add(&plug->mq_list, rq);
+ plug->rq_count++;
+}
+
/**
* blk_mq_request_bypass_insert - Insert a request at dispatch list.
* @rq: Pointer to request to be inserted.
@@ -2353,7 +2387,12 @@ void blk_mq_request_bypass_insert(struct request *rq, bool at_head,
bool run_queue)
{
struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
+ struct blk_plug *plug = current->plug;

+ if (plug) {
+ blk_add_rq_to_plug(plug, rq);
+ return;
+ }
spin_lock(&hctx->lock);
if (at_head)
list_add(&rq->queuelist, &hctx->dispatch);
@@ -2676,40 +2715,6 @@ void blk_mq_try_issue_list_directly(struct blk_mq_hw_ctx *hctx,
hctx->queue->mq_ops->commit_rqs(hctx);
}

-/*
- * Allow 2x BLK_MAX_REQUEST_COUNT requests on plug queue for multiple
- * queues. This is important for md arrays to benefit from merging
- * requests.
- */
-static inline unsigned short blk_plug_max_rq_count(struct blk_plug *plug)
-{
- if (plug->multiple_queues)
- return BLK_MAX_REQUEST_COUNT * 2;
- return BLK_MAX_REQUEST_COUNT;
-}
-
-static void blk_add_rq_to_plug(struct blk_plug *plug, struct request *rq)
-{
- struct request *last = rq_list_peek(&plug->mq_list);
-
- if (!plug->rq_count) {
- trace_block_plug(rq->q);
- } else if (plug->rq_count >= blk_plug_max_rq_count(plug) ||
- (!blk_queue_nomerges(rq->q) &&
- blk_rq_bytes(last) >= BLK_PLUG_FLUSH_SIZE)) {
- blk_mq_flush_plug_list(plug, false);
- trace_block_plug(rq->q);
- }
-
- if (!plug->multiple_queues && last && last->q != rq->q)
- plug->multiple_queues = true;
- if (!plug->has_elevator && (rq->rq_flags & RQF_ELV))
- plug->has_elevator = true;
- rq->rq_next = NULL;
- rq_list_add(&plug->mq_list, rq);
- plug->rq_count++;
-}
-
static bool blk_mq_attempt_bio_merge(struct request_queue *q,
struct bio *bio, unsigned int nr_segs)
{
--
2.25.1