On 3/10/22 5:07 PM, Jens Axboe wrote:
> In any case, just doing larger reads would likely help quite a bit, but
> would still be nice to get to the bottom of why we're not seeing the
> level of merging we expect.
Song, can you try this one? It'll do the dispatch in a somewhat saner
fashion, bundling identical queues. And we'll keep iterating the plug
list for a merge if we have multiple disks, until we've seen a queue
match and checked.
diff --git a/block/blk-merge.c b/block/blk-merge.c
index 0e871d4e7cb8..68b623d00db5 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -1073,12 +1073,20 @@ bool blk_attempt_plug_merge(struct request_queue *q, struct bio *bio,
if (!plug || rq_list_empty(plug->mq_list))
return false;
- /* check the previously added entry for a quick merge attempt */
- rq = rq_list_peek(&plug->mq_list);
- if (rq->q == q) {
- if (blk_attempt_bio_merge(q, rq, bio, nr_segs, false) ==
- BIO_MERGE_OK)
- return true;
+ rq_list_for_each(&plug->mq_list, rq) {
+ if (rq->q == q) {
+ if (blk_attempt_bio_merge(q, rq, bio, nr_segs, false) ==
+ BIO_MERGE_OK)
+ return true;
+ break;
+ }
+
+ /*
+ * Only keep iterating plug list for merges if we have multiple
+ * queues
+ */
+ if (!plug->multiple_queues)
+ break;
}
return false;
}
diff --git a/block/blk-mq.c b/block/blk-mq.c
index bb263abbb40f..9c784262fd6b 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2576,13 +2576,36 @@ static void __blk_mq_flush_plug_list(struct request_queue *q,
q->mq_ops->queue_rqs(&plug->mq_list);
}
+static void blk_mq_dispatch_plug_list(struct blk_plug *plug, bool from_sched)
+{
+ struct blk_mq_hw_ctx *this_hctx = NULL;
+ struct blk_mq_ctx *this_ctx = NULL;
+ struct request *requeue_list = NULL;
+ unsigned int depth = 0;
+ LIST_HEAD(list);
+
+ do {
+ struct request *rq = rq_list_pop(&plug->mq_list);
+
+ if (!this_hctx) {
+ this_hctx = rq->mq_hctx;
+ this_ctx = rq->mq_ctx;
+ } else if (this_hctx != rq->mq_hctx || this_ctx != rq->mq_ctx) {
+ rq_list_add(&requeue_list, rq);
+ continue;
+ }
+ list_add_tail(&rq->queuelist, &list);
+ depth++;
+ } while (!rq_list_empty(plug->mq_list));
+
+ plug->mq_list = requeue_list;
+ trace_block_unplug(this_hctx->queue, depth, !from_sched);
+ blk_mq_sched_insert_requests(this_hctx, this_ctx, &list, from_sched);
+}
+
void blk_mq_flush_plug_list(struct blk_plug *plug, bool from_schedule)
{
- struct blk_mq_hw_ctx *this_hctx;
- struct blk_mq_ctx *this_ctx;
struct request *rq;
- unsigned int depth;
- LIST_HEAD(list);
if (rq_list_empty(plug->mq_list))
return;
@@ -2618,35 +2641,9 @@ void blk_mq_flush_plug_list(struct blk_plug *plug, bool from_schedule)
return;
}
- this_hctx = NULL;
- this_ctx = NULL;
- depth = 0;
do {
- rq = rq_list_pop(&plug->mq_list);
-
- if (!this_hctx) {
- this_hctx = rq->mq_hctx;
- this_ctx = rq->mq_ctx;
- } else if (this_hctx != rq->mq_hctx || this_ctx != rq->mq_ctx) {
- trace_block_unplug(this_hctx->queue, depth,
- !from_schedule);
- blk_mq_sched_insert_requests(this_hctx, this_ctx,
- &list, from_schedule);
- depth = 0;
- this_hctx = rq->mq_hctx;
- this_ctx = rq->mq_ctx;
-
- }
-
- list_add(&rq->queuelist, &list);
- depth++;
+ blk_mq_dispatch_plug_list(plug, from_schedule);
} while (!rq_list_empty(plug->mq_list));
-
- if (!list_empty(&list)) {
- trace_block_unplug(this_hctx->queue, depth, !from_schedule);
- blk_mq_sched_insert_requests(this_hctx, this_ctx, &list,
- from_schedule);
- }
}
void blk_mq_try_issue_list_directly(struct blk_mq_hw_ctx *hctx,
--
Jens Axboe
