Commit 7f2a6a69 authored by Song Liu's avatar Song Liu Committed by Jens Axboe
Browse files

blk-mq: allow 4x BLK_MAX_REQUEST_COUNT at blk_plug for multiple_queues 

Limiting number of request to BLK_MAX_REQUEST_COUNT at blk_plug hurts
performance for large md arrays. [1] shows resync speed of md array drops
for md array with more than 16 HDDs.

Fix this by allowing more request at plug queue. The multiple_queue flag
is used to only apply higher limit to multiple queue cases.

[1] https://lore.kernel.org/linux-raid/CAFDAVznS71BXW8Jxv6k9dXc2iR3ysX3iZRBww_rzA8WifBFxGg@mail.gmail.com/


Tested-by: default avatarMarcin Wanat <marcin.wanat@gmail.com>
Signed-off-by: default avatarSong Liu <songliubraving@fb.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 0dca4462

block/blk-mq.c

+13 −1
Original line number Diff line number Diff line
@@ -2135,6 +2135,18 @@ static void blk_add_rq_to_plug(struct blk_plug *plug, struct request *rq) 
	}

}



/*

 * Allow 4x 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 * 4;

	return BLK_MAX_REQUEST_COUNT;

}



/**

 * blk_mq_submit_bio - Create and send a request to block device.

 * @bio: Bio pointer.
@@ -2231,7 +2243,7 @@ blk_qc_t blk_mq_submit_bio(struct bio *bio) 
		else

			last = list_entry_rq(plug->mq_list.prev);



		if (request_count >= BLK_MAX_REQUEST_COUNT || (last &&

		if (request_count >= blk_plug_max_rq_count(plug) || (last &&

		    blk_rq_bytes(last) >= BLK_PLUG_FLUSH_SIZE)) {

			blk_flush_plug_list(plug, false);

			trace_block_plug(q);