Hi Jens
On 08/20/2018 10:45 PM, Jens Axboe wrote:
> 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.
>
Thanks very much for your comment.
I have reworked this patch based on your kindly suggestion and posted the V4.
Thanks
Jianchao
