From: Damien Le Moal <damien.lemoal@wdc.com>
Date: Tue, 20 Nov 2018 01:52:37 +0000 (+0900)
Subject: block: prevent merging of requests with different priorities
X-Git-Tag: v5.4-rc1~1880^2~204
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=668ffc03418bc779f699797c72ecf968cd6525a9;p=platform%2Fkernel%2Flinux-rpi.git

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>
---

diff --git a/block/blk-core.c b/block/blk-core.c
index 4450d3c..dde30b0 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 b1df622..6be04ef 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -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;
 }