Commit 668ffc03 authored by Damien Le Moal's avatar Damien Le Moal Committed by Jens Axboe
Browse files

block: prevent merging of requests with different priorities 



Growing in size a high priority request by merging it with a lower
priority BIO or request will increase the request execution time. This
is the opposite result of the desired effect of high I/O priorities,
namely getting low I/O latencies. Prevent merging of requests and BIOs
that have different I/O priorities to fix this.

Signed-off-by: default avatarDamien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 76dc8913

block/blk-core.c

+0 −3
Original line number Diff line number Diff line
@@ -662,7 +662,6 @@ bool bio_attempt_back_merge(struct request_queue *q, struct request *req, 
	req->biotail->bi_next = bio;

	req->biotail = bio;

	req->__data_len += bio->bi_iter.bi_size;

	req->ioprio = ioprio_best(req->ioprio, bio_prio(bio));



	blk_account_io_start(req, false);

	return true;
@@ -686,7 +685,6 @@ bool bio_attempt_front_merge(struct request_queue *q, struct request *req, 


	req->__sector = bio->bi_iter.bi_sector;

	req->__data_len += bio->bi_iter.bi_size;

	req->ioprio = ioprio_best(req->ioprio, bio_prio(bio));



	blk_account_io_start(req, false);

	return true;
@@ -706,7 +704,6 @@ bool bio_attempt_discard_merge(struct request_queue *q, struct request *req, 
	req->biotail->bi_next = bio;

	req->biotail = bio;

	req->__data_len += bio->bi_iter.bi_size;

	req->ioprio = ioprio_best(req->ioprio, bio_prio(bio));

	req->nr_phys_segments = segments + 1;



	blk_account_io_start(req, false);

block/blk-merge.c

+6 −2
Original line number Diff line number Diff line
@@ -752,6 +752,9 @@ static struct request *attempt_merge(struct request_queue *q, 
	if (req->write_hint != next->write_hint)

		return NULL;



	if (req->ioprio != next->ioprio)

		return NULL;



	/*

	 * If we are allowed to merge, then append bio list

	 * from next to rq and release next. merge_requests_fn
@@ -807,8 +810,6 @@ static struct request *attempt_merge(struct request_queue *q, 
	 */

	blk_account_io_merge(next);



	req->ioprio = ioprio_best(req->ioprio, next->ioprio);



	/*

	 * ownership of bio passed from next to req, return 'next' for

	 * the caller to free
@@ -883,6 +884,9 @@ bool blk_rq_merge_ok(struct request *rq, struct bio *bio) 
	if (rq->write_hint != bio->bi_write_hint)

		return false;



	if (rq->ioprio != bio_prio(bio))

		return false;



	return true;

}

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