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

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Message-ID: <8fa8c620-22ff-0963-d1ee-c6fe6f13b49c@huaweicloud.com>
Date: Wed, 18 Dec 2024 09:12:24 +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 2024/12/18 6:13, Bart Van Assche 写道:
> On 12/16/24 6:40 PM, Yu Kuai wrote:
>> +static unsigned int min_async_depth = 64;
>> +module_param(min_async_depth, int, 0444);
>> +MODULE_PARM_DESC(min_async_depth, "The minimal number of tags 
>> available for asynchronous requests");
> 
> Users may not like it that this parameter is read-only.
> 
>> @@ -513,9 +523,12 @@ static void dd_depth_updated(struct blk_mq_hw_ctx 
>> *hctx)
>>       struct deadline_data *dd = q->elevator->elevator_data;
>>       struct blk_mq_tags *tags = hctx->sched_tags;
>> -    dd->async_depth = max(1UL, 3 * q->nr_requests / 4);
> 
> Shouldn't this assignment be retained instead of removing it? 
> Additionally, some time ago a user requested to initialize 
> dd->async_depth to q->nr_requests instead of 3/4 of that value because
> the lower value introduced a performance regression.
dd->async_depth is initialized to 0 now, functionally I think
it's the same as q->nr_requests. And I do explain this in commit
message, maybe it's not clear?

BTW, if user sets new nr_requests and async_depth < new nr_requests,
async_depth won't be reset after this patch.

Thanks,
Kuai

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