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 <[email protected]> --- block/blk-core.c | 3 --- block/blk-merge.c | 14 ++++++++++++-- 2 files changed, 12 insertions(+), 5 deletions(-) diff --git a/block/blk-core.c b/block/blk-core.c index 4450d3c08f25..dde30b08aa14 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -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); diff --git a/block/blk-merge.c b/block/blk-merge.c index b1df622cbd85..129f554d250d 100644 --- a/block/blk-merge.c +++ b/block/blk-merge.c @@ -752,6 +752,12 @@ static struct request *attempt_merge(struct request_queue *q, if (req->write_hint != next->write_hint) return NULL; + /* + * Don't allow merge of different I/O priorities. + */ + 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 +813,6 @@ 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 +887,12 @@ bool blk_rq_merge_ok(struct request *rq, struct bio *bio) if (rq->write_hint != bio->bi_write_hint) return false; + /* + * Don't allow merge of different I/O priorities. + */ + if (rq->ioprio != bio_prio(bio)) + return false; + return true; } -- 2.19.1
