Commit 596dce11 authored by Ming Lei's avatar Ming Lei Committed by Jens Axboe
Browse files

block: simplify elevator reattachment for updating nr_hw_queues 



In blk_mq_update_nr_hw_queues(), nr_hw_queues changes and elevator data
depends on it, and elevator has to be reattached, so call elevator_switch()
to force attachment.

Add elv_update_nr_hw_queues() simply for blk_mq_update_nr_hw_queues() to
reattach elevator, since elevator switch isn't likely when running
blk_mq_update_nr_hw_queues(). This way removes the current switch
none and switch back code.

Reviewed-by: default avatarHannes Reinecke <hare@suse.de>
Reviewed-by: default avatarNilay Shroff <nilay@linux.ibm.com>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Signed-off-by: default avatarMing Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250505141805.2751237-14-ming.lei@redhat.com


Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent ac55b71a

block/blk-mq.c

+1 −89
Original line number Diff line number Diff line
@@ -4987,88 +4987,10 @@ int blk_mq_update_nr_requests(struct request_queue *q, unsigned int nr) 
	return ret;

}



/*

 * request_queue and elevator_type pair.

 * It is just used by __blk_mq_update_nr_hw_queues to cache

 * the elevator_type associated with a request_queue.

 */

struct blk_mq_qe_pair {

	struct list_head node;

	struct request_queue *q;

	struct elevator_type *type;

};



/*

 * Cache the elevator_type in qe pair list and switch the

 * io scheduler to 'none'

 */

static bool blk_mq_elv_switch_none(struct list_head *head,

		struct request_queue *q)

{

	struct blk_mq_qe_pair *qe;



	qe = kmalloc(sizeof(*qe), GFP_NOIO | __GFP_NOWARN | __GFP_NORETRY);

	if (!qe)

		return false;



	/* Accessing q->elevator needs protection from ->elevator_lock. */

	mutex_lock(&q->elevator_lock);



	if (!q->elevator) {

		kfree(qe);

		goto unlock;

	}



	INIT_LIST_HEAD(&qe->node);

	qe->q = q;

	qe->type = q->elevator->type;

	/* keep a reference to the elevator module as we'll switch back */

	__elevator_get(qe->type);

	list_add(&qe->node, head);

	elevator_disable(q);

unlock:

	mutex_unlock(&q->elevator_lock);



	return true;

}



static struct blk_mq_qe_pair *blk_lookup_qe_pair(struct list_head *head,

						struct request_queue *q)

{

	struct blk_mq_qe_pair *qe;



	list_for_each_entry(qe, head, node)

		if (qe->q == q)

			return qe;



	return NULL;

}



static void blk_mq_elv_switch_back(struct list_head *head,

				  struct request_queue *q)

{

	struct blk_mq_qe_pair *qe;

	struct elevator_type *t;



	qe = blk_lookup_qe_pair(head, q);

	if (!qe)

		return;

	t = qe->type;

	list_del(&qe->node);

	kfree(qe);



	mutex_lock(&q->elevator_lock);

	elevator_switch(q, t->elevator_name);

	/* drop the reference acquired in blk_mq_elv_switch_none */

	elevator_put(t);

	mutex_unlock(&q->elevator_lock);

}



static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set,

							int nr_hw_queues)

{

	struct request_queue *q;

	LIST_HEAD(head);

	int prev_nr_hw_queues = set->nr_hw_queues;

	unsigned int memflags;

	int i;
@@ -5086,15 +5008,6 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, 
	list_for_each_entry(q, &set->tag_list, tag_set_list)

		blk_mq_freeze_queue_nomemsave(q);



	/*

	 * Switch IO scheduler to 'none', cleaning up the data associated

	 * with the previous scheduler. We will switch back once we are done

	 * updating the new sw to hw queue mappings.

	 */

	list_for_each_entry(q, &set->tag_list, tag_set_list)

		if (!blk_mq_elv_switch_none(&head, q))

			goto switch_back;



	list_for_each_entry(q, &set->tag_list, tag_set_list) {

		blk_mq_debugfs_unregister_hctxs(q);

		blk_mq_sysfs_unregister_hctxs(q);
@@ -5128,9 +5041,8 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, 
		blk_mq_debugfs_register_hctxs(q);

	}



switch_back:

	list_for_each_entry(q, &set->tag_list, tag_set_list)

		blk_mq_elv_switch_back(&head, q);

		elv_update_nr_hw_queues(q);



	list_for_each_entry(q, &set->tag_list, tag_set_list)

		blk_mq_unfreeze_queue_nomemrestore(q);

block/blk.h

+1 −2
Original line number Diff line number Diff line
@@ -322,8 +322,7 @@ bool blk_bio_list_merge(struct request_queue *q, struct list_head *list, 


bool blk_insert_flush(struct request *rq);



int elevator_switch(struct request_queue *q, const char *name);

void elevator_disable(struct request_queue *q);

void elv_update_nr_hw_queues(struct request_queue *q);

void elevator_exit(struct request_queue *q);

int elv_register_queue(struct request_queue *q, bool uevent);

void elv_unregister_queue(struct request_queue *q);

block/elevator.c

+19 −1
Original line number Diff line number Diff line
@@ -621,7 +621,7 @@ void elevator_init_mq(struct request_queue *q) 
 * If switching fails, we are most likely running out of memory and not able

 * to restore the old io scheduler, so leaving the io scheduler being none.

 */

int elevator_switch(struct request_queue *q, const char *name)

static int elevator_switch(struct request_queue *q, const char *name)

{

	struct elevator_type *new_e = NULL;

	int ret = 0;
@@ -682,6 +682,24 @@ static int elevator_change(struct request_queue *q, const char *elevator_name) 
	return elevator_switch(q, elevator_name);

}



/*

 * The I/O scheduler depends on the number of hardware queues, this forces a

 * reattachment when nr_hw_queues changes.

 */

void elv_update_nr_hw_queues(struct request_queue *q)

{

	WARN_ON_ONCE(q->mq_freeze_depth == 0);



	mutex_lock(&q->elevator_lock);

	if (q->elevator && !blk_queue_dying(q) && !blk_queue_registered(q)) {

		const char *name = q->elevator->type->elevator_name;



		/* force to reattach elevator after nr_hw_queue is updated */

		elevator_switch(q, name);

	}

	mutex_unlock(&q->elevator_lock);

}



static void elv_iosched_load_module(char *elevator_name)

{

	struct elevator_type *found;