linux-kernel - Re: [PATCH v2] blk-ioprio: Introduce promote-to-rt policy

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Date:   Thu, 23 Feb 2023 09:08:06 +0800
From:   Hou Tao <houtao@...weicloud.com>
To:     Bagas Sanjaya <bagasdotme@...il.com>, linux-block@...r.kernel.org
Cc:     Bart Van Assche <bvanassche@....org>, Jan Kara <jack@...e.cz>,
        Jens Axboe <axboe@...nel.dk>, cgroups@...r.kernel.org,
        Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Jonathan Corbet <corbet@....net>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, houtao1@...wei.com
Subject: Re: [PATCH v2] blk-ioprio: Introduce promote-to-rt policy

Hi,

On 2/22/2023 3:38 PM, Bagas Sanjaya wrote:
> On 2/20/23 20:54, Hou Tao wrote:
>> diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
>> index 74cec76be9f2..ccfb9fdfbc16 100644
>> --- a/Documentation/admin-guide/cgroup-v2.rst
>> +++ b/Documentation/admin-guide/cgroup-v2.rst
>> @@ -2021,31 +2021,33 @@ that attribute:
>>    no-change
>>  	Do not modify the I/O priority class.
>>  
>> -  none-to-rt
>> -	For requests that do not have an I/O priority class (NONE),
>> -	change the I/O priority class into RT. Do not modify
>> -	the I/O priority class of other requests.
>> +  promote-to-rt
>> +	For requests that have a no-RT I/O priority class, change it into RT.
> "non-RT" maybe? Or the original wording is better?
Because promote-to-rt doesn't work like none-to-rt, so using the original word
is incorrect. Will fix it to non-RT in v3.
>> +	Also change the priority level of these requests to 4. Do not modify
>> +	the I/O priority of requests that have priority class RT.>  
>>    restrict-to-be
>>  	For requests that do not have an I/O priority class or that have I/O
>> -	priority class RT, change it into BE. Do not modify the I/O priority
>> -	class of requests that have priority class IDLE.
>> +	priority class RT, change it into BE. Also change the priority level
>> +	of these requests to 0. Do not modify the I/O priority class of
>> +	requests that have priority class IDLE.
>>  
>>    idle
>>  	Change the I/O priority class of all requests into IDLE, the lowest
>>  	I/O priority class.
>>  
>> +  none-to-rt
>> +	Deprecated. Just an alias for promote-to-rt.
>> +
>>  The following numerical values are associated with the I/O priority policies:
>>  
>> -+-------------+---+
>> -| no-change   | 0 |
>> -+-------------+---+
>> -| none-to-rt  | 1 |
>> -+-------------+---+
>> -| rt-to-be    | 2 |
>> -+-------------+---+
>> -| all-to-idle | 3 |
>> -+-------------+---+
>> ++----------------+---+
>> +| no-change      | 0 |
>> ++----------------+---+
>> +| rt-to-be       | 2 |
>> ++----------------+---+
>> +| all-to-idle    | 3 |
>> ++----------------+---+
>>  
>>  The numerical value that corresponds to each I/O priority class is as follows:
>>  
>> @@ -2061,9 +2063,13 @@ The numerical value that corresponds to each I/O priority class is as follows:
>>  
>>  The algorithm to set the I/O priority class for a request is as follows:
>>  
>> -- Translate the I/O priority class policy into a number.
>> -- Change the request I/O priority class into the maximum of the I/O priority
>> -  class policy number and the numerical I/O priority class.
>> +- If I/O priority class policy is promote-to-rt, change the request I/O
>> +  priority class to IOPRIO_CLASS_RT and change the request I/O priority
>> +  level to 4.
>> +- If I/O priorityt class is not promote-to-rt, translate the I/O priority
>> +  class policy into a number, then change the request I/O priority class
>> +  into the maximum of the I/O priority class policy number and the numerical
>> +  I/O priority class.
>>  
>>  PID
>>  ---
> The rest is LGTM.
Thanks for you review.
>