linux-kernel - Re: [PATCH RFC -next 0/7] blk-iocost: support to build iocost as kernel module

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Date: Fri, 14 Jun 2024 09:07:03 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: Bart Van Assche <bvanassche@....org>, Greg KH
 <gregkh@...uxfoundation.org>, Yu Kuai <yukuai1@...weicloud.com>
Cc: axboe@...nel.dk, tj@...nel.org, josef@...icpanda.com,
 lizefan.x@...edance.com, hannes@...xchg.org, linux-block@...r.kernel.org,
 linux-kernel@...r.kernel.org, cgroups@...r.kernel.org, yi.zhang@...wei.com,
 yangerkun@...wei.com, "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH RFC -next 0/7] blk-iocost: support to build iocost as
 kernel module

Hi,

在 2024/06/14 0:15, Bart Van Assche 写道:
> On 6/12/24 10:54 PM, Greg KH wrote:
>> On Thu, Jun 13, 2024 at 09:49:30AM +0800, Yu Kuai wrote:
>>> From: Yu Kuai <yukuai3@...wei.com>
>>>
>>> Yu Kuai (7):
>>>    kernfs: export pr_cont_kernfs_path()
>>>    cgroup: export cgroup_parse_float
>>>    block: export some API
>>>    blk-iocost: factor out helpers to handle params from ioc_qos_write()
>>>    blk-iocost: parse params before initializing iocost
>>>    blk-iocost: support to free iocost
>>>    blk-iocost: support to build iocost as kernel module
>>
>> No where do you say _why_ building this as a module is a good idea.
>>
>> Why do this at all?
> 
> With CONFIG_BLK_CGROUP_IOCOST=y (as in the Android kernel), the
> blk-iocost kernel module causes a (small) runtime overhead, even if it
> is not being used.

I think this is not true... Because iocost is lazy initialized, and if
iocost is not initialized, there should not be such overhead.

Thanks,
Kuai

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