Commit e42cfb1d authored by Damien Le Moal's avatar Damien Le Moal Committed by Jens Axboe
Browse files

block: Remove unnecessary elevator operation checks 



The insert_requests and dispatch_request elevator operations are
mandatory for the correct execution of an elevator, and all implemented
elevators (bfq, kyber and mq-deadline) implement them. As a result,
there is no need to check for these operations before calling them when
a queue has an elevator set. This simplifies the code in
__blk_mq_sched_dispatch_requests() and blk_mq_sched_insert_request().

To avoid out-of-tree elevators to crash the kernel in case of bad
implementation, add a check in elv_register() to verify that these
operations are implemented.

A small, probably not significant, IOPS improvement of 0.1% is observed
with this patch applied (4.117 MIOPS to 4.123 MIOPS, average of 20 fio
runs doing 4K random direct reads with psync and 32 jobs).

Signed-off-by: default avatarDamien Le Moal <damien.lemoal@wdc.com>
Reviewed-by: default avatarJohannes Thumshirn <johannes.thumshirn@wdc.com>
Link: https://lore.kernel.org/r/20210618015922.713999-1-damien.lemoal@wdc.com


Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent f0c1c4d2

block/blk-mq-sched.c

+6 −7
Original line number Diff line number Diff line
@@ -294,8 +294,7 @@ static int blk_mq_do_dispatch_ctx(struct blk_mq_hw_ctx *hctx) 
static int __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.dispatch_request;

	const bool has_sched = q->elevator;

	int ret = 0;

	LIST_HEAD(rq_list);
@@ -326,12 +325,12 @@ 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 (has_sched_dispatch)

			if (has_sched)

				ret = blk_mq_do_dispatch_sched(hctx);

			else

				ret = blk_mq_do_dispatch_ctx(hctx);

		}

	} else if (has_sched_dispatch) {

	} else if (has_sched) {

		ret = blk_mq_do_dispatch_sched(hctx);

	} else if (hctx->dispatch_busy) {

		/* dequeue request one by one from sw queue if queue is busy */
@@ -463,7 +462,7 @@ void blk_mq_sched_insert_request(struct request *rq, bool at_head, 
		goto run;

	}



	if (e && e->type->ops.insert_requests) {

	if (e) {

		LIST_HEAD(list);



		list_add(&rq->queuelist, &list);
@@ -494,9 +493,9 @@ void blk_mq_sched_insert_requests(struct blk_mq_hw_ctx *hctx, 
	percpu_ref_get(&q->q_usage_counter);



	e = hctx->queue->elevator;

	if (e && e->type->ops.insert_requests)

	if (e) {

		e->type->ops.insert_requests(hctx, list, false);

	else {

	} else {

		/*

		 * try to issue requests directly if the hw queue isn't

		 * busy in case of 'none' scheduler, and this way may save

block/elevator.c

+4 −0
Original line number Diff line number Diff line
@@ -522,6 +522,10 @@ void elv_unregister_queue(struct request_queue *q) 


int elv_register(struct elevator_type *e)

{

	/* insert_requests and dispatch_request are mandatory */

	if (WARN_ON_ONCE(!e->ops.insert_requests || !e->ops.dispatch_request))

		return -EINVAL;



	/* create icq_cache if requested */

	if (e->icq_size) {

		if (WARN_ON(e->icq_size < sizeof(struct io_cq)) ||