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block: simplify elevator reattachment for updating nr_hw_queues

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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: Hannes Reinecke <hare@suse.de>
Reviewed-by: Nilay Shroff <nilay@linux.ibm.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250505141805.2751237-14-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Ming Lei 2025-05-05 22:17:51 +08:00 • committed by Jens Axboe
parent ac55b71a31
commit 596dce110b
3 changed files with 21 additions and 92 deletions
Download patch file Download diff file Expand all files Collapse all files

90
block/blk-mq.c
View file

@ -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 @@ reregister:
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);

3
block/blk.h
View file

@ -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);

20
block/elevator.c
View file

@ -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;