[QUESTION] blk_mq_freeze_queue in elevator_init_mq

[yangerkun]

On 2021/11/17 18:19, Ming Lei wrote:
> On Wed, Nov 17, 2021 at 05:00:22PM +0800, yangerkun wrote:
>>
>>
>> On 2021/11/17 16:06, Ming Lei wrote:
>>> On Wed, Nov 17, 2021 at 11:37:13AM +0800, yangerkun wrote:
>>>> Nowdays we meet the boot regression while enable lots of mtdblock
>>>
>>> What is your boot regression? Any dmesg log?
>>
>> The result is that when boot with 5.10 kernel compare with 4.4, 5.10
>> will consume about 1.6s more...
> 
> OK, I understand the issue now, and please try the attached patch
> which depends on the following one:

Hi, this patch can help solve the problem!

> 
> https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git/commit/?h=block-5.16&id=2a19b28f7929866e1cec92a3619f4de9f2d20005
> 
> 
> diff --git a/block/elevator.c b/block/elevator.c
> index 1f39f6e8ebb9..19a78d5516ba 100644
> --- a/block/elevator.c
> +++ b/block/elevator.c
> @@ -694,12 +694,18 @@ void elevator_init_mq(struct request_queue *q)
>   	if (!e)
>   		return;
>   
> +	/*
> +	 * We are called before adding disk, when there isn't any FS I/O,
> +	 * so freezing queue plus canceling dispatch work is enough to
> +	 * drain any dispatch activities originated from passthrough
> +	 * requests, then no need to quiesce queue which may add long boot
> +	 * latency, especially when lots of disks are involved.
> +	 */
>   	blk_mq_freeze_queue(q);
> -	blk_mq_quiesce_queue(q);
> +	blk_mq_cancel_work_sync(q);
>   
>   	err = blk_mq_init_sched(q, e);
>   
> -	blk_mq_unquiesce_queue(q);
>   	blk_mq_unfreeze_queue(q);
>   
>   	if (err) {
> 
> 
> 
> thanks,
> Ming
> 
> .
>