Commit e093b784 authored by Bart Van Assche's avatar Bart Van Assche Committed by Jens Axboe
Browse files

block: Simplify blk_mq_dispatch_rq_list() and its callers 



The 'nr_budgets' argument of blk_mq_dispatch_rq_list() is either the
number of elements in the 'list' argument or zero. Instead of passing
the number of list elements to blk_mq_dispatch_rq_list(), pass a boolean
argument that indicates whether or not blk_mq_dispatch_rq_list() should
request the block driver for a budget for each request in 'list'.

Remove the code for counting list elements from blk_mq_dispatch_rq_list()
callers where possible. Remove the code that decrements nr_budgets from
blk_mq_dispatch_rq_list() because it is superfluous. Each request that
is processed by blk_mq_dispatch_rq_list() is in one of these two states
if 'get_budget' is false:
* Either the request is on 'list' and the budget for the request has to
  be released from the error path.
* Or the request is not on 'list' and q->mq_ops->queue_rq() has already
  released the budget (ret != BLK_STS_OK) or q->mq_ops->queue_rq() will
  release the budget asynchronously (ret == BLK_STS_OK).

Cc: Christoph Hellwig <hch@lst.de>
Cc: Ming Lei <ming.lei@redhat.com>
Cc: John Garry <john.g.garry@oracle.com>
Signed-off-by: default avatarBart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20250415205134.3650042-1-bvanassche@acm.org


Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 9d7a0577

block/blk-mq-sched.c

+5 −7
Original line number Diff line number Diff line
@@ -59,19 +59,17 @@ static bool blk_mq_dispatch_hctx_list(struct list_head *rq_list) 
		list_first_entry(rq_list, struct request, queuelist)->mq_hctx;

	struct request *rq;

	LIST_HEAD(hctx_list);

	unsigned int count = 0;



	list_for_each_entry(rq, rq_list, queuelist) {

		if (rq->mq_hctx != hctx) {

			list_cut_before(&hctx_list, rq_list, &rq->queuelist);

			goto dispatch;

		}

		count++;

	}

	list_splice_tail_init(rq_list, &hctx_list);



dispatch:

	return blk_mq_dispatch_rq_list(hctx, &hctx_list, count);

	return blk_mq_dispatch_rq_list(hctx, &hctx_list, false);

}



#define BLK_MQ_BUDGET_DELAY	3		/* ms units */
@@ -167,7 +165,7 @@ static int __blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx) 
			dispatched |= blk_mq_dispatch_hctx_list(&rq_list);

		} while (!list_empty(&rq_list));

	} else {

		dispatched = blk_mq_dispatch_rq_list(hctx, &rq_list, count);

		dispatched = blk_mq_dispatch_rq_list(hctx, &rq_list, false);

	}



	if (busy)
@@ -261,7 +259,7 @@ static int blk_mq_do_dispatch_ctx(struct blk_mq_hw_ctx *hctx) 
		/* round robin for fair dispatch */

		ctx = blk_mq_next_ctx(hctx, rq->mq_ctx);



	} while (blk_mq_dispatch_rq_list(rq->mq_hctx, &rq_list, 1));

	} while (blk_mq_dispatch_rq_list(rq->mq_hctx, &rq_list, false));



	WRITE_ONCE(hctx->dispatch_from, ctx);

	return ret;
@@ -298,7 +296,7 @@ static int __blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx) 
	 */

	if (!list_empty(&rq_list)) {

		blk_mq_sched_mark_restart_hctx(hctx);

		if (!blk_mq_dispatch_rq_list(hctx, &rq_list, 0))

		if (!blk_mq_dispatch_rq_list(hctx, &rq_list, true))

			return 0;

		need_dispatch = true;

	} else {
@@ -312,7 +310,7 @@ static int __blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx) 
	if (need_dispatch)

		return blk_mq_do_dispatch_ctx(hctx);

	blk_mq_flush_busy_ctxs(hctx, &rq_list);

	blk_mq_dispatch_rq_list(hctx, &rq_list, 0);

	blk_mq_dispatch_rq_list(hctx, &rq_list, true);

	return 0;

}

block/blk-mq.c

+7 −9
Original line number Diff line number Diff line
@@ -2080,7 +2080,7 @@ static void blk_mq_commit_rqs(struct blk_mq_hw_ctx *hctx, int queued, 
 * Returns true if we did some work AND can potentially do more.

 */

bool blk_mq_dispatch_rq_list(struct blk_mq_hw_ctx *hctx, struct list_head *list,

			     unsigned int nr_budgets)

			     bool get_budget)

{

	enum prep_dispatch prep;

	struct request_queue *q = hctx->queue;
@@ -2102,7 +2102,7 @@ bool blk_mq_dispatch_rq_list(struct blk_mq_hw_ctx *hctx, struct list_head *list, 
		rq = list_first_entry(list, struct request, queuelist);



		WARN_ON_ONCE(hctx != rq->mq_hctx);

		prep = blk_mq_prep_dispatch_rq(rq, !nr_budgets);

		prep = blk_mq_prep_dispatch_rq(rq, get_budget);

		if (prep != PREP_DISPATCH_OK)

			break;
@@ -2111,12 +2111,6 @@ bool blk_mq_dispatch_rq_list(struct blk_mq_hw_ctx *hctx, struct list_head *list, 
		bd.rq = rq;

		bd.last = list_empty(list);



		/*

		 * once the request is queued to lld, no need to cover the

		 * budget any more

		 */

		if (nr_budgets)

			nr_budgets--;

		ret = q->mq_ops->queue_rq(hctx, &bd);

		switch (ret) {

		case BLK_STS_OK:
@@ -2150,7 +2144,11 @@ bool blk_mq_dispatch_rq_list(struct blk_mq_hw_ctx *hctx, struct list_head *list, 
			((hctx->flags & BLK_MQ_F_TAG_QUEUE_SHARED) ||

			blk_mq_is_shared_tags(hctx->flags));



		if (nr_budgets)

		/*

		 * If the caller allocated budgets, free the budgets of the

		 * requests that have not yet been passed to the block driver.

		 */

		if (!get_budget)

			blk_mq_release_budgets(q, list);



		spin_lock(&hctx->lock);

block/blk-mq.h

+1 −1
Original line number Diff line number Diff line
@@ -48,7 +48,7 @@ void blk_mq_exit_queue(struct request_queue *q); 
int blk_mq_update_nr_requests(struct request_queue *q, unsigned int nr);

void blk_mq_wake_waiters(struct request_queue *q);

bool blk_mq_dispatch_rq_list(struct blk_mq_hw_ctx *hctx, struct list_head *,

			     unsigned int);

			     bool);

void blk_mq_flush_busy_ctxs(struct blk_mq_hw_ctx *hctx, struct list_head *list);

struct request *blk_mq_dequeue_from_ctx(struct blk_mq_hw_ctx *hctx,

					struct blk_mq_ctx *start);