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Commit de148297 authored by Ming Lei's avatar Ming Lei Committed by Jens Axboe
Browse files

blk-mq: introduce .get_budget and .put_budget in blk_mq_ops 



For SCSI devices, there is often a per-request-queue depth, which needs
to be respected before queuing one request.

Currently blk-mq always dequeues the request first, then calls
.queue_rq() to dispatch the request to lld. One obvious issue with this
approach is that I/O merging may not be successful, because when the
per-request-queue depth can't be respected, .queue_rq() has to return
BLK_STS_RESOURCE, and then this request has to stay in hctx->dispatch
list. This means it never gets a chance to be merged with other IO.

This patch introduces .get_budget and .put_budget callback in blk_mq_ops,
then we can try to get reserved budget first before dequeuing request.
If the budget for queueing I/O can't be satisfied, we don't need to
dequeue request at all. Hence the request can be left in the IO
scheduler queue, for more merging opportunities.

Signed-off-by: default avatarMing Lei <ming.lei@redhat.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 63ba8e31

block/blk-mq-sched.c

+45 −10
Original line number Diff line number Diff line
@@ -89,31 +89,57 @@ static bool blk_mq_sched_restart_hctx(struct blk_mq_hw_ctx *hctx) 
	return false;

}



static void blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)

/* return true if hctx need to run again */

static bool blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)

{

	struct request_queue *q = hctx->queue;

	struct elevator_queue *e = q->elevator;

	LIST_HEAD(rq_list);



	do {

		struct request *rq = e->type->ops.mq.dispatch_request(hctx);

		struct request *rq;

		blk_status_t ret;



		if (e->type->ops.mq.has_work &&

				!e->type->ops.mq.has_work(hctx))

			break;



		ret = blk_mq_get_dispatch_budget(hctx);

		if (ret == BLK_STS_RESOURCE)

			return true;



		if (!rq)

		rq = e->type->ops.mq.dispatch_request(hctx);

		if (!rq) {

			blk_mq_put_dispatch_budget(hctx);

			break;

		} else if (ret != BLK_STS_OK) {

			blk_mq_end_request(rq, ret);

			continue;

		}



		/*

		 * Now this rq owns the budget which has to be released

		 * if this rq won't be queued to driver via .queue_rq()

		 * in blk_mq_dispatch_rq_list().

		 */

		list_add(&rq->queuelist, &rq_list);

	} while (blk_mq_dispatch_rq_list(q, &rq_list));

	} while (blk_mq_dispatch_rq_list(q, &rq_list, true));



	return false;

}



void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)

/* return true if hw queue need to be run again */

bool blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)

{

	struct request_queue *q = hctx->queue;

	struct elevator_queue *e = q->elevator;

	const bool has_sched_dispatch = e && e->type->ops.mq.dispatch_request;

	LIST_HEAD(rq_list);

	bool run_queue = false;



	/* RCU or SRCU read lock is needed before checking quiesced flag */

	if (unlikely(blk_mq_hctx_stopped(hctx) || blk_queue_quiesced(q)))

		return;

		return false;



	hctx->run++;
@@ -143,14 +169,23 @@ void 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(q, &rq_list) && has_sched_dispatch)

			blk_mq_do_dispatch_sched(hctx);

		if (blk_mq_dispatch_rq_list(q, &rq_list, false) &&

				has_sched_dispatch)

			run_queue = blk_mq_do_dispatch_sched(hctx);

	} else if (has_sched_dispatch) {

		blk_mq_do_dispatch_sched(hctx);

		run_queue = blk_mq_do_dispatch_sched(hctx);

	} else {

		blk_mq_flush_busy_ctxs(hctx, &rq_list);

		blk_mq_dispatch_rq_list(q, &rq_list);

		blk_mq_dispatch_rq_list(q, &rq_list, false);

	}



	if (run_queue && !blk_mq_sched_needs_restart(hctx) &&

			!test_bit(BLK_MQ_S_TAG_WAITING, &hctx->state)) {

		blk_mq_sched_mark_restart_hctx(hctx);

		return true;

	}



	return false;

}



bool blk_mq_sched_try_merge(struct request_queue *q, struct bio *bio,

block/blk-mq-sched.h

+1 −1
Original line number Diff line number Diff line
@@ -22,7 +22,7 @@ void blk_mq_sched_insert_requests(struct request_queue *q, 
				  struct blk_mq_ctx *ctx,

				  struct list_head *list, bool run_queue_async);



void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx);

bool blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx);



int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e);

void blk_mq_exit_sched(struct request_queue *q, struct elevator_queue *e);

block/blk-mq.c

+38 −5
Original line number Diff line number Diff line
@@ -1048,7 +1048,8 @@ static bool blk_mq_dispatch_wait_add(struct blk_mq_hw_ctx *hctx) 
	return true;

}



bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list)

bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list,

		bool got_budget)

{

	struct blk_mq_hw_ctx *hctx;

	struct request *rq;
@@ -1057,6 +1058,8 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list) 
	if (list_empty(list))

		return false;



	WARN_ON(!list_is_singular(list) && got_budget);



	/*

	 * Now process all the entries, sending them to the driver.

	 */
@@ -1074,16 +1077,30 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list) 
			 * The initial allocation attempt failed, so we need to

			 * rerun the hardware queue when a tag is freed.

			 */

			if (!blk_mq_dispatch_wait_add(hctx))

			if (!blk_mq_dispatch_wait_add(hctx)) {

				if (got_budget)

					blk_mq_put_dispatch_budget(hctx);

				break;

			}



			/*

			 * It's possible that a tag was freed in the window

			 * between the allocation failure and adding the

			 * hardware queue to the wait queue.

			 */

			if (!blk_mq_get_driver_tag(rq, &hctx, false))

			if (!blk_mq_get_driver_tag(rq, &hctx, false)) {

				if (got_budget)

					blk_mq_put_dispatch_budget(hctx);

				break;

			}

		}



		if (!got_budget) {

			ret = blk_mq_get_dispatch_budget(hctx);

			if (ret == BLK_STS_RESOURCE)

				break;

			if (ret != BLK_STS_OK)

				goto fail_rq;

		}



		list_del_init(&rq->queuelist);
@@ -1111,6 +1128,7 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list) 
			break;

		}



 fail_rq:

		if (unlikely(ret != BLK_STS_OK)) {

			errors++;

			blk_mq_end_request(rq, BLK_STS_IOERR);
@@ -1169,6 +1187,7 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list) 
static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx)

{

	int srcu_idx;

	bool run_queue;



	/*

	 * We should be running this queue from one of the CPUs that
@@ -1185,15 +1204,18 @@ static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx) 


	if (!(hctx->flags & BLK_MQ_F_BLOCKING)) {

		rcu_read_lock();

		blk_mq_sched_dispatch_requests(hctx);

		run_queue = blk_mq_sched_dispatch_requests(hctx);

		rcu_read_unlock();

	} else {

		might_sleep();



		srcu_idx = srcu_read_lock(hctx->queue_rq_srcu);

		blk_mq_sched_dispatch_requests(hctx);

		run_queue = blk_mq_sched_dispatch_requests(hctx);

		srcu_read_unlock(hctx->queue_rq_srcu, srcu_idx);

	}



	if (run_queue)

		blk_mq_run_hw_queue(hctx, true);

}



/*
@@ -1582,6 +1604,13 @@ static void __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx, 
	if (!blk_mq_get_driver_tag(rq, NULL, false))

		goto insert;



	ret = blk_mq_get_dispatch_budget(hctx);

	if (ret == BLK_STS_RESOURCE) {

		blk_mq_put_driver_tag(rq);

		goto insert;

	} else if (ret != BLK_STS_OK)

		goto fail_rq;



	new_cookie = request_to_qc_t(hctx, rq);



	/*
@@ -1598,6 +1627,7 @@ static void __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx, 
		__blk_mq_requeue_request(rq);

		goto insert;

	default:

 fail_rq:

		*cookie = BLK_QC_T_NONE;

		blk_mq_end_request(rq, ret);

		return;
@@ -2582,6 +2612,9 @@ int blk_mq_alloc_tag_set(struct blk_mq_tag_set *set) 
	if (!set->ops->queue_rq)

		return -EINVAL;



	if (!set->ops->get_budget ^ !set->ops->put_budget)

		return -EINVAL;



	if (set->queue_depth > BLK_MQ_MAX_DEPTH) {

		pr_info("blk-mq: reduced tag depth to %u\n",

			BLK_MQ_MAX_DEPTH);

block/blk-mq.h

+19 −1
Original line number Diff line number Diff line
@@ -30,7 +30,7 @@ void blk_mq_freeze_queue(struct request_queue *q); 
void blk_mq_free_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 request_queue *, struct list_head *);

bool blk_mq_dispatch_rq_list(struct request_queue *, struct list_head *, bool);

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

bool blk_mq_hctx_has_pending(struct blk_mq_hw_ctx *hctx);

bool blk_mq_get_driver_tag(struct request *rq, struct blk_mq_hw_ctx **hctx,
@@ -137,4 +137,22 @@ static inline bool blk_mq_hw_queue_mapped(struct blk_mq_hw_ctx *hctx) 
void blk_mq_in_flight(struct request_queue *q, struct hd_struct *part,

			unsigned int inflight[2]);



static inline void blk_mq_put_dispatch_budget(struct blk_mq_hw_ctx *hctx)

{

	struct request_queue *q = hctx->queue;



	if (q->mq_ops->put_budget)

		q->mq_ops->put_budget(hctx);

}



static inline blk_status_t blk_mq_get_dispatch_budget(

		struct blk_mq_hw_ctx *hctx)

{

	struct request_queue *q = hctx->queue;



	if (q->mq_ops->get_budget)

		return q->mq_ops->get_budget(hctx);

	return BLK_STS_OK;

}



#endif

include/linux/blk-mq.h

+11 −0
Original line number Diff line number Diff line
@@ -90,6 +90,8 @@ struct blk_mq_queue_data { 


typedef blk_status_t (queue_rq_fn)(struct blk_mq_hw_ctx *,

		const struct blk_mq_queue_data *);

typedef blk_status_t (get_budget_fn)(struct blk_mq_hw_ctx *);

typedef void (put_budget_fn)(struct blk_mq_hw_ctx *);

typedef enum blk_eh_timer_return (timeout_fn)(struct request *, bool);

typedef int (init_hctx_fn)(struct blk_mq_hw_ctx *, void *, unsigned int);

typedef void (exit_hctx_fn)(struct blk_mq_hw_ctx *, unsigned int);
@@ -111,6 +113,15 @@ struct blk_mq_ops { 
	 */

	queue_rq_fn		*queue_rq;



	/*

	 * Reserve budget before queue request, once .queue_rq is

	 * run, it is driver's responsibility to release the

	 * reserved budget. Also we have to handle failure case

	 * of .get_budget for avoiding I/O deadlock.

	 */

	get_budget_fn		*get_budget;

	put_budget_fn		*put_budget;



	/*

	 * Called on request timeout

	 */