blk-mq: make plug work for mutiple disks and queues
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>
diff --git a/block/blk-core.c b/block/blk-core.c
index 9dcfb8e..f0be754 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1522,7 +1522,8 @@
* 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 @@
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 @@
* 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);