block: wire-up support for passthrough plugging

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.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20220511054750.20432-3-joshi.k@samsung.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 84d7495..2cf011b 100644 (file)
--- 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)
 {