linux-kernel - [PATCH V2 2/2] blk-mq: immediately dispatch big size request

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Date:   Thu, 3 Nov 2016 17:03:54 -0700
From:   Shaohua Li <shli@...com>
To:     <linux-block@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC:     <Kernel-team@...com>, <axboe@...com>
Subject: [PATCH V2 2/2] blk-mq: immediately dispatch big size request

This is corresponding part for blk-mq. Disk with multiple hardware
queues doesn't need this as we only hold 1 request at most.

Signed-off-by: Shaohua Li <shli@...com>
---
 block/blk-mq.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index f3d27a6..a72538a 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1401,13 +1401,18 @@ static blk_qc_t blk_sq_make_request(struct request_queue *q, struct bio *bio)
 	 */
 	plug = current->plug;
 	if (plug) {
+		struct request *last = NULL;
+
 		blk_mq_bio_to_request(rq, bio);
 		if (!request_count)
 			trace_block_plug(q);
+		else
+			last = list_entry_rq(plug->mq_list.prev);
 
 		blk_mq_put_ctx(data.ctx);
 
-		if (request_count >= BLK_MAX_REQUEST_COUNT) {
+		if (request_count >= BLK_MAX_REQUEST_COUNT || (last &&
+		    blk_rq_bytes(last) >= BLK_PLUG_FLUSH_SIZE)) {
 			blk_flush_plug_list(plug, false);
 			trace_block_plug(q);
 		}
-- 
2.9.3