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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: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Damien Le Moal 2018-11-20 10:52:37 +09:00 committed by Jens Axboe
parent 76dc891395
commit 668ffc0341
2 changed files with 6 additions and 5 deletions
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3
block/blk-core.c
View File

@ -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);

8
block/blk-merge.c
View File

@ -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;
}