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

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Message-ID: <97a2b888-4dac-451c-bb9c-40d8dc52cd60@acm.org>
Date: Thu, 13 Jun 2024 09:15:11 -0700
From: Bart Van Assche <bvanassche@....org>
To: 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, yukuai3@...wei.com,
 yi.zhang@...wei.com, yangerkun@...wei.com
Subject: Re: [PATCH RFC -next 0/7] blk-iocost: support to build iocost as
 kernel module

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.

Thanks,

Bart.