[PATCH 1/2] Revert "blk-mq, elevator: Count requests per hctx to improve performance"

[Jan Kara <jack@suse.cz>]

This reverts commit b445547ec1bbd3e7bf4b1c142550942f70527d95.

Since both mq-deadline and BFQ completely ignore hctx they are passed to
their dispatch function and dispatch whatever request they deem fit
checking whether any request for a particular hctx is queued is just
pointless since we'll very likely get a request from a different hctx
anyway. In the following commit we'll deal with lock contention in these
IO schedulers in presence of multiple HW queues in a different way.

Signed-off-by: Jan Kara <jack@suse.cz>
---
 block/bfq-iosched.c    | 5 -----
 block/blk-mq.c         | 1 -
 block/mq-deadline.c    | 6 ------
 include/linux/blk-mq.h | 4 ----
 4 files changed, 16 deletions(-)

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 9e81d1052091..a99dfaa75a8c 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -4640,9 +4640,6 @@ static bool bfq_has_work(struct blk_mq_hw_ctx *hctx)
 {
 	struct bfq_data *bfqd = hctx->queue->elevator->elevator_data;
 
-	if (!atomic_read(&hctx->elevator_queued))
-		return false;
-
 	/*
 	 * Avoiding lock: a race on bfqd->busy_queues should cause at
 	 * most a call to dispatch for nothing
@@ -5557,7 +5554,6 @@ static void bfq_insert_requests(struct blk_mq_hw_ctx *hctx,
 		rq = list_first_entry(list, struct request, queuelist);
 		list_del_init(&rq->queuelist);
 		bfq_insert_request(hctx, rq, at_head);
-		atomic_inc(&hctx->elevator_queued);
 	}
 }
 
@@ -5925,7 +5921,6 @@ static void bfq_finish_requeue_request(struct request *rq)
 
 		bfq_completed_request(bfqq, bfqd);
 		bfq_finish_requeue_request_body(bfqq);
-		atomic_dec(&rq->mq_hctx->elevator_queued);
 
 		spin_unlock_irqrestore(&bfqd->lock, flags);
 	} else {
diff --git a/block/blk-mq.c b/block/blk-mq.c
index f285a9123a8b..57f3482b2c26 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2653,7 +2653,6 @@ blk_mq_alloc_hctx(struct request_queue *q, struct blk_mq_tag_set *set,
 		goto free_hctx;
 
 	atomic_set(&hctx->nr_active, 0);
-	atomic_set(&hctx->elevator_queued, 0);
 	if (node == NUMA_NO_NODE)
 		node = set->numa_node;
 	hctx->numa_node = node;
diff --git a/block/mq-deadline.c b/block/mq-deadline.c
index 800ac902809b..b57470e154c8 100644
--- a/block/mq-deadline.c
+++ b/block/mq-deadline.c
@@ -386,8 +386,6 @@ static struct request *dd_dispatch_request(struct blk_mq_hw_ctx *hctx)
 	spin_lock(&dd->lock);
 	rq = __dd_dispatch_request(dd);
 	spin_unlock(&dd->lock);
-	if (rq)
-		atomic_dec(&rq->mq_hctx->elevator_queued);
 
 	return rq;
 }
@@ -535,7 +533,6 @@ static void dd_insert_requests(struct blk_mq_hw_ctx *hctx,
 		rq = list_first_entry(list, struct request, queuelist);
 		list_del_init(&rq->queuelist);
 		dd_insert_request(hctx, rq, at_head);
-		atomic_inc(&hctx->elevator_queued);
 	}
 	spin_unlock(&dd->lock);
 }
@@ -582,9 +579,6 @@ static bool dd_has_work(struct blk_mq_hw_ctx *hctx)
 {
 	struct deadline_data *dd = hctx->queue->elevator->elevator_data;
 
-	if (!atomic_read(&hctx->elevator_queued))
-		return false;
-
 	return !list_empty_careful(&dd->dispatch) ||
 		!list_empty_careful(&dd->fifo_list[0]) ||
 		!list_empty_careful(&dd->fifo_list[1]);
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index d705b174d346..b4b9604bbfd7 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -140,10 +140,6 @@ struct blk_mq_hw_ctx {
 	 * shared across request queues.
 	 */
 	atomic_t		nr_active;
-	/**
-	 * @elevator_queued: Number of queued requests on hctx.
-	 */
-	atomic_t                elevator_queued;
 
 	/** @cpuhp_online: List to store request if CPU is going to die */
 	struct hlist_node	cpuhp_online;
-- 
2.26.2