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blk-mq: make plug work for mutiple disks and queues

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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.

V2: use NULL parameter in !mq case. Fix a bug. Add comments in
blk_attempt_plug_merge to make it less (hopefully) confusion.

Cc: Jens Axboe <axboe@fb.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Shaohua Li <shli@fb.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
This commit is contained in:
Shaohua Li 2015-05-08 10:51:33 -07:00 committed by Jens Axboe
parent f984df1f0f
commit 5b3f341f09
3 changed files with 23 additions and 9 deletions
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15
block/blk-core.c
View File

@ -1522,7 +1522,8 @@ 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;
@ -1542,8 +1543,16 @@ 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)++;
/*
* Only blk-mq multiple hardware queues case checks the
* rq in the same queue, there should be only one such
* rq in a queue
**/
if (same_queue_rq)
*same_queue_rq = rq;
}
if (rq->q != q || !blk_rq_merge_ok(rq, bio))
continue;
@ -1608,7 +1617,7 @@ 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, NULL))
return;
spin_lock_irq(q->queue_lock);

14
block/blk-mq.c
View File

@ -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 (!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);
@ -1309,9 +1310,12 @@ 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);
/*
* The plug list might get flushed before this. If that
* happens, same_queue_rq is invalid and plug list is empty
**/
if (same_queue_rq && !list_empty(&plug->mq_list)) {
old_rq = same_queue_rq;
list_del_init(&old_rq->queuelist);
}
list_add_tail(&rq->queuelist, &plug->mq_list);
@ -1360,7 +1364,7 @@ static void blk_sq_make_request(struct request_queue *q, struct bio *bio)
}
if (!is_flush_fua && !blk_queue_nomerges(q) &&
blk_attempt_plug_merge(q, bio, &request_count))
blk_attempt_plug_merge(q, bio, &request_count, NULL))
return;
rq = blk_mq_map_request(q, bio, &data);

3
block/blk.h
View File

@ -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);