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

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Message-ID: <b1a4c70e-e41e-e434-0f98-6c61a4bd7dbc@huaweicloud.com>
Date: Fri, 20 Dec 2024 14:08:58 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: Bart Van Assche <bvanassche@....org>, 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

Hi,

在 2024/12/20 3:25, Bart Van Assche 写道:
> 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?

Yes, I think this make sense, at least kyber and deadline can both
benefit from this. And I might must add a new async_depth_updated() api
to the elevator ops.

Thanks,
Kuai

> 
> Thanks,
> 
> Bart.
> 
> 
> .
>