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Subject: Re: Situation of CONFIG_BLK_WBT_MQ after commit b11d31ae01e6
 ("blk-wbt: remove unnecessary check in wbt_enable_default()")
To:     Lukas Bulwahn <lukas.bulwahn@gmail.com>,
        Christoph Hellwig <hch@lst.de>, Jens Axboe <axboe@kernel.dk>,
        linux-block@vger.kernel.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "yukuai (C)" <yukuai3@huawei.com>
References: <CAKXUXMzfKq_J9nKHGyr5P5rvUETY4B-fxoQD4sO+NYjFOfVtZA@mail.gmail.com>
From:   Yu Kuai <yukuai1@huaweicloud.com>
Message-ID: <8a86ba08-cde4-97a4-d7e2-dc340609381c@huaweicloud.com>
Date:   Wed, 10 May 2023 11:24:55 +0800
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Hi,

在 2023/05/08 12:37, Lukas Bulwahn 写道:
> Dear Yu Kuai, dear Christoph, dear Jens,
> 
> 
> The commit b11d31ae01e6 ("blk-wbt: remove unnecessary check in
> wbt_enable_default()") removes the only reference to the config
> BLK_WBT_MQ in the kernel tree.
> 
> The commit comes with the statement "If CONFIG_BLK_WBT_MQ is disabled,
> wbt_init() won't do anything.". The statement "If CONFIG_BLK_WBT is
> disabled, wbt_init() won't do anything." (note: CONFIG_BLK_WBT vs.
> CONFIG_BLK_WBT_MQ) is certainly true, but I do not see that "If
> CONFIG_BLK_WBT_MQ is disabled, wbt_init() won't do anything.", but I
> believe it would simply do what wbt_init() does with CONFIG_BLK_WBT
> being enabled.
> 
> Now, it seems that with this commit applied, the intended switch of
> the config BLK_WBT_MQ is gone, and the config really now has no effect
> at all.
> 
> So, I am a bit puzzled:
> 
> 1. Either the config BLK_WBT_MQ does have an effect somewhere, but one
> cannot find its reference with 'git grep -i "BLK_WBT_MQ" .' --- so, my
> investigation is just incomplete or wrong, or
> 
> 2. We really do not need this further build config BLK_WBT_MQ beyond
> the other configs already there --- then this config should just be
> removed, or
> 
> 3. the commit unintentionally broke the purpose of the config
> BLK_WBT_MQ --- then this commit above should be reverted.

Thanks for the report, it's the above case and it's my mistake.
I will fix this.

Kuai
> 
> I would be happy if you could provide some guidance on what is the
> situation with config BLK_WBT_MQ.
> 
> Currently, I am guessing it is option 2 and the config BLK_WBT_MQ
> simply can be deleted, but I am really unsure. Probably, this build
> option is not used by many people and its effect is hardly noticed, if
> one does not specifically check for that in the running system.
> 
> 
> Best regards,
> 
> Lukas
> .
>