Last patch makes plug work for multiple queue case. However it only
works for single disk case, because it assumes only one request in the
plug list. If a task is accessing multiple disks, eg MD/DM, the
assumption is wrong. Let blk_attempt_plug_merge() record request from
the same queue.
Cc: Jens Axboe <ax...@fb.com>
Cc: Christoph Hellwig <h...@lst.de>
Signed-off-by: Shaohua Li <s...@fb.com>
---
block/blk-core.c | 10 +++++++---
block/blk-mq.c | 11 ++++++-----
block/blk.h | 3 ++-
3 files changed, 15 insertions(+), 9 deletions(-)
diff --git a/block/blk-core.c b/block/blk-core.c
index d51ed61..a5e1574 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1521,7 +1521,8 @@ bool bio_attempt_front_merge(struct request_queue *q,
struct request *req,
* Caller must ensure !blk_queue_nomerges(q) beforehand.
*/
bool blk_attempt_plug_merge(struct request_queue *q, struct bio *bio,
- unsigned int *request_count)
+ unsigned int *request_count,
+ struct request **same_queue_rq)
{
struct blk_plug *plug;
struct request *rq;
@@ -1541,8 +1542,10 @@ bool blk_attempt_plug_merge(struct request_queue *q,
struct bio *bio,
list_for_each_entry_reverse(rq, plug_list, queuelist) {
int el_ret;
- if (rq->q == q)
+ if (rq->q == q) {
(*request_count)++;
+ *same_queue_rq = rq;
+ }
if (rq->q != q || !blk_rq_merge_ok(rq, bio))
continue;
@@ -1583,6 +1586,7 @@ void blk_queue_bio(struct request_queue *q, struct bio
*bio)
int el_ret, rw_flags, where = ELEVATOR_INSERT_SORT;
struct request *req;
unsigned int request_count = 0;
+ struct request *same_queue_rq;
/*
* low level driver can indicate that it wants pages above a
@@ -1607,7 +1611,7 @@ void blk_queue_bio(struct request_queue *q, struct bio
*bio)
* any locks.
*/
if (!blk_queue_nomerges(q) &&
- blk_attempt_plug_merge(q, bio, &request_count))
+ blk_attempt_plug_merge(q, bio, &request_count, &same_queue_rq))
return;
spin_lock_irq(q->queue_lock);
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 5545828..c45739c 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1269,6 +1269,7 @@ static void blk_mq_make_request(struct request_queue *q,
struct bio *bio)
struct request *rq;
unsigned int request_count = 0;
struct blk_plug *plug;
+ struct request *same_queue_rq = NULL;
blk_queue_bounce(q, &bio);
@@ -1278,7 +1279,7 @@ static void blk_mq_make_request(struct request_queue *q,
struct bio *bio)
}
if (likely(!is_flush_fua) && !blk_queue_nomerges(q) &&
- blk_attempt_plug_merge(q, bio, &request_count))
+ blk_attempt_plug_merge(q, bio, &request_count, &same_queue_rq))
return;
rq = blk_mq_map_request(q, bio, &data);
@@ -1308,9 +1309,8 @@ static void blk_mq_make_request(struct request_queue *q,
struct bio *bio)
* issued. So the plug list will have one request at most
*/
if (plug) {
- if (!list_empty(&plug->mq_list)) {
- old_rq = list_first_entry(&plug->mq_list,
- struct request, queuelist);
+ if (same_queue_rq) {
+ old_rq = same_queue_rq;
list_del_init(&old_rq->queuelist);
}
list_add_tail(&rq->queuelist, &plug->mq_list);
@@ -1350,6 +1350,7 @@ static void blk_sq_make_request(struct request_queue *q,
struct bio *bio)
unsigned int request_count = 0;
struct blk_map_ctx data;
struct request *rq;
+ struct request *same_queue_rq;
blk_queue_bounce(q, &bio);
@@ -1359,7 +1360,7 @@ static void blk_sq_make_request(struct request_queue *q,
struct bio *bio)
}
if (likely(!is_flush_fua) && !blk_queue_nomerges(q) &&
- blk_attempt_plug_merge(q, bio, &request_count))
+ blk_attempt_plug_merge(q, bio, &request_count, &same_queue_rq))
return;
rq = blk_mq_map_request(q, bio, &data);
diff --git a/block/blk.h b/block/blk.h
index 43b0361..aa8633c 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -78,7 +78,8 @@ bool bio_attempt_front_merge(struct request_queue *q, struct
request *req,
bool bio_attempt_back_merge(struct request_queue *q, struct request *req,
struct bio *bio);
bool blk_attempt_plug_merge(struct request_queue *q, struct bio *bio,
- unsigned int *request_count);
+ unsigned int *request_count,
+ struct request **same_queue_rq);
void blk_account_io_start(struct request *req, bool new_io);
void blk_account_io_completion(struct request *req, unsigned int bytes);
--
1.8.1
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