On 8/20/18 1:20 AM, Jianchao Wang wrote:
> @@ -2913,6 +2906,29 @@ 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(q);
>
> + /*
> + * switch io scheduler to NULL to clean up the data in it.
> + * will get it back after update mapping between cpu and hw queues.
> + */
"Switch IO scheduler to 'none', cleaning up the data associated with
the previous scheduler. We'll switch back once we're done updating
the new sw to hw queue mappings.
> + list_for_each_entry(q, &set->tag_list, tag_set_list) {
> + if (!q->elevator) {
> + q->elv_type = NULL;
> + continue;
> + }
> + q->elv_type = q->elevator->type;
> + mutex_lock(&q->sysfs_lock);
> + /*
> + * After elevator_switch_mq, the previous elevator_queue will be
> + * released by elevator_release. The reference of the io scheduler
> + * module get by elevator_get will also be put. So we need to get
> + * a reference of the io scheduler module here to prevent it to be
> + * removed.
> + */
> + __module_get(q->elv_type->elevator_owner);
> + elevator_switch_mq(q, NULL);
> + mutex_unlock(&q->sysfs_lock);
> + }
I don't hate this, but I also find it pretty annoying to put local state
into the queue itself. It would be much nicer _not_ to have ->elv_type
in the queue itself. That would need an allocation, however...
Apart from those two things, looks fine to me.
--
Jens Axboe
