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Subject: Re: [PATCH v3 1/5] wbt: don't show valid wbt_lat_usec in sysfs while
 wbt is disabled
To:     Jan Kara <jack@suse.cz>, Yu Kuai <yukuai1@huaweicloud.com>
Cc:     paolo.valente@linaro.org, axboe@kernel.dk,
        linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
        yi.zhang@huawei.com, "yukuai (C)" <yukuai3@huawei.com>
References: <20220922113558.1085314-1-yukuai3@huawei.com>
 <20220922113558.1085314-2-yukuai3@huawei.com>
 <20220926094434.jrl6gnlbjqkex3wa@quack3>
 <6736753f-b5ae-39f1-b0c4-508b7f45d701@huaweicloud.com>
 <20220926114726.ta2w3vcbxgkh3sov@quack3>
From:   Yu Kuai <yukuai1@huaweicloud.com>
Message-ID: <84ae1c2c-9b57-6cb7-173b-68b5c7634d64@huaweicloud.com>
Date:   Mon, 26 Sep 2022 21:01:41 +0800
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Hi, Jan

在 2022/09/26 19:47, Jan Kara 写道:
> On Mon 26-09-22 18:25:18, Yu Kuai wrote:
>> Hi, Jan
>>
>> 在 2022/09/26 17:44, Jan Kara 写道:
>>> On Thu 22-09-22 19:35:54, Yu Kuai wrote:
>>>> Currently, if wbt is initialized and then disabled by
>>>> wbt_disable_default(), sysfs will still show valid wbt_lat_usec, which
>>>> will confuse users that wbt is still enabled.
>>>>
>>>> This patch shows wbt_lat_usec as zero and forbid to set it while wbt
>>>> is disabled.
>>>
>>> So I agree we should show 0 in wbt_lat_usec if wbt is disabled by
>>> wbt_disable_default(). But why do you forbid setting of wbt_lat_usec?
>>> IMHO if wbt_lat_usec is set, admin wants to turn on wbt so we should just
>>> update rwb->enable_state to WBT_STATE_ON_MANUAL.
>>
>> I was thinking that don't enable wbt if elevator is bfq. Since we know
>> that performance is bad, thus it doesn't make sense to me to do that,
>> and user might doesn't aware of the problem.
> 
> Yeah, I don't think it is a good idea (that is the reason why it is
> disabled by default) but in priciple I don't see a reason why we should
> block admin from enabling it.

I'll enable it in next version.

Thanks,
Kuai