linux-kernel - Re: [PATCH RFC v2 4/4] block/mq-deadline: introduce min_async

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Message-ID: <818ca8e9-d691-421f-9b66-f13c76f523f3@acm.org>
Date: Thu, 19 Dec 2024 11:25:25 -0800
From: Bart Van Assche <bvanassche@....org>
To: Yu Kuai <yukuai1@...weicloud.com>, axboe@...nel.dk,
 akpm@...ux-foundation.org, ming.lei@...hat.com, yang.yang@...o.com,
 osandov@...com, paolo.valente@...aro.org
Cc: linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
 yi.zhang@...wei.com, yangerkun@...wei.com, "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH RFC v2 4/4] block/mq-deadline: introduce min_async_depth

On 12/18/24 5:21 PM, Yu Kuai wrote:
> Hi,
> 
> 在 2024/12/19 2:00, Bart Van Assche 写道:
>> On 12/17/24 5:14 PM, Yu Kuai wrote:
>>> I can't make this read-write, because set lower value will cause
>>> problems for existing elevator, because wake_batch has to be
>>> updated as well.
>>
>> Should the request queue perhaps be frozen before wake_batch is updated?
> 
> Yes, we should. The good thing is for now it's frozen already:
>   - update nr_requests context;
>   - switch elevator;
> 
> However, if you mean do this while writing async_depth, freeze queue
> is not enough, we have to ping all the hctx as well by q->sysfs_lock,
> which is not possible.
> 
> Or if you mean do this while write the new min_async_depth, then we have
> to update wat_batch for all the queues in the system, too crazy for
> me...

Should min_async_depth perhaps be a request queue attribute instead of
an mq-deadline I/O scheduler attribute?

Thanks,

Bart.