[v4] blk-ioprio: Introduce promote-to-rt policy

  From: Hou Tao <houtao1@huawei.com>

Since commit a78418e6a04c ("block: Always initialize bio IO priority on
submit"), bio->bi_ioprio will never be IOPRIO_CLASS_NONE when calling
blkcg_set_ioprio(), so there will be no way to promote the io-priority
of one cgroup to IOPRIO_CLASS_RT, because bi_ioprio will always be
greater than or equals to IOPRIO_CLASS_RT.

It seems possible to call blkcg_set_ioprio() first then try to
initialize bi_ioprio later in bio_set_ioprio(), but this doesn't work
for bio in which bi_ioprio is already initialized (e.g., direct-io), so
introduce a new promote-to-rt policy to promote the iopriority of bio to
IOPRIO_CLASS_RT if the ioprio is not already RT.

For none-to-rt policy, although it doesn't work now, but considering
that its purpose was also to override the io-priority to RT and allowing
for a smoother transition, just keep it and treat it as an alias of
the promote-to-rt policy.

Acked-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Hou Tao <houtao1@huawei.com>
---
v4:
 * rebased on 33afd4b76393
 * Add Reviewed-by from Jan Kara

v3: https://lore.kernel.org/linux-block/20230223135154.3749088-1-houtao@huaweicloud.com
 * Use 'non-RT' instead of 'no-RT' in document (from Bagas)
 * Remove repeated sentence in commit message
 * Add Reviewed-by and Acked-by tags
 
v2: https://lore.kernel.org/linux-block/20230220135428.2632906-1-houtao@huaweicloud.com

 * Simplify the implementation of promote-to-rt (from Bart)
 * Make none-to-rt to work again by treating it as an alias of
   the promote-to-rt policy (from Bart & Jan)
 * fix the style of new content in cgroup-v2.rst (from Bagas)
 * set the default priority level to 4 instead of 0 for promote-to-rt

v1: https://lore.kernel.org/linux-block/20230201045227.2203123-1-houtao@huaweicloud.com

 Documentation/admin-guide/cgroup-v2.rst | 42 ++++++++++++++-----------
 block/blk-ioprio.c                      | 23 ++++++++++++--
 2 files changed, 44 insertions(+), 21 deletions(-)
  

On 4/28/23 14:44, Hou Tao wrote:
> diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
> index f67c0829350b..7544ce00e0cb 100644
> --- a/Documentation/admin-guide/cgroup-v2.rst
> +++ b/Documentation/admin-guide/cgroup-v2.rst
> @@ -2024,31 +2024,33 @@ 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 non-RT I/O priority class, change it into RT.
> +	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:
>  
> @@ -2064,9 +2066,13 @@ 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 doc LGTM, thanks!

Reviewed-by: Bagas Sanjaya <bagasdotme@gmail.com>
  

ping ?

On 4/28/2023 3:44 PM, Hou Tao wrote:
> From: Hou Tao <houtao1@huawei.com>
>
> Since commit a78418e6a04c ("block: Always initialize bio IO priority on
> submit"), bio->bi_ioprio will never be IOPRIO_CLASS_NONE when calling
> blkcg_set_ioprio(), so there will be no way to promote the io-priority
> of one cgroup to IOPRIO_CLASS_RT, because bi_ioprio will always be
> greater than or equals to IOPRIO_CLASS_RT.
>
> It seems possible to call blkcg_set_ioprio() first then try to
> initialize bi_ioprio later in bio_set_ioprio(), but this doesn't work
> for bio in which bi_ioprio is already initialized (e.g., direct-io), so
> introduce a new promote-to-rt policy to promote the iopriority of bio to
> IOPRIO_CLASS_RT if the ioprio is not already RT.
>
> For none-to-rt policy, although it doesn't work now, but considering
> that its purpose was also to override the io-priority to RT and allowing
> for a smoother transition, just keep it and treat it as an alias of
> the promote-to-rt policy.
>
> Acked-by: Tejun Heo <tj@kernel.org>
> Reviewed-by: Bart Van Assche <bvanassche@acm.org>
> Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
> Reviewed-by: Jan Kara <jack@suse.cz>
> Signed-off-by: Hou Tao <houtao1@huawei.com>
> ---
> v4:
>  * rebased on 33afd4b76393
>  * Add Reviewed-by from Jan Kara
>
> v3: https://lore.kernel.org/linux-block/20230223135154.3749088-1-houtao@huaweicloud.com
>  * Use 'non-RT' instead of 'no-RT' in document (from Bagas)
>  * Remove repeated sentence in commit message
>  * Add Reviewed-by and Acked-by tags
>  
> v2: https://lore.kernel.org/linux-block/20230220135428.2632906-1-houtao@huaweicloud.com
>
>  * Simplify the implementation of promote-to-rt (from Bart)
>  * Make none-to-rt to work again by treating it as an alias of
>    the promote-to-rt policy (from Bart & Jan)
>  * fix the style of new content in cgroup-v2.rst (from Bagas)
>  * set the default priority level to 4 instead of 0 for promote-to-rt
>
> v1: https://lore.kernel.org/linux-block/20230201045227.2203123-1-houtao@huaweicloud.com
>
>  Documentation/admin-guide/cgroup-v2.rst | 42 ++++++++++++++-----------
>  block/blk-ioprio.c                      | 23 ++++++++++++--
>  2 files changed, 44 insertions(+), 21 deletions(-)
>
> diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
> index f67c0829350b..7544ce00e0cb 100644
> --- a/Documentation/admin-guide/cgroup-v2.rst
> +++ b/Documentation/admin-guide/cgroup-v2.rst
> @@ -2024,31 +2024,33 @@ 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 non-RT I/O priority class, change it into RT.
> +	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:
>  
> @@ -2064,9 +2066,13 @@ 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
>  ---
> diff --git a/block/blk-ioprio.c b/block/blk-ioprio.c
> index 055529b9b92b..4051fada01f1 100644
> --- a/block/blk-ioprio.c
> +++ b/block/blk-ioprio.c
> @@ -23,25 +23,28 @@
>  /**
>   * enum prio_policy - I/O priority class policy.
>   * @POLICY_NO_CHANGE: (default) do not modify the I/O priority class.
> - * @POLICY_NONE_TO_RT: modify IOPRIO_CLASS_NONE into IOPRIO_CLASS_RT.
> + * @POLICY_PROMOTE_TO_RT: modify no-IOPRIO_CLASS_RT to IOPRIO_CLASS_RT.
>   * @POLICY_RESTRICT_TO_BE: modify IOPRIO_CLASS_NONE and IOPRIO_CLASS_RT into
>   *		IOPRIO_CLASS_BE.
>   * @POLICY_ALL_TO_IDLE: change the I/O priority class into IOPRIO_CLASS_IDLE.
> + * @POLICY_NONE_TO_RT: an alias for POLICY_PROMOTE_TO_RT.
>   *
>   * See also <linux/ioprio.h>.
>   */
>  enum prio_policy {
>  	POLICY_NO_CHANGE	= 0,
> -	POLICY_NONE_TO_RT	= 1,
> +	POLICY_PROMOTE_TO_RT	= 1,
>  	POLICY_RESTRICT_TO_BE	= 2,
>  	POLICY_ALL_TO_IDLE	= 3,
> +	POLICY_NONE_TO_RT	= 4,
>  };
>  
>  static const char *policy_name[] = {
>  	[POLICY_NO_CHANGE]	= "no-change",
> -	[POLICY_NONE_TO_RT]	= "none-to-rt",
> +	[POLICY_PROMOTE_TO_RT]	= "promote-to-rt",
>  	[POLICY_RESTRICT_TO_BE]	= "restrict-to-be",
>  	[POLICY_ALL_TO_IDLE]	= "idle",
> +	[POLICY_NONE_TO_RT]	= "none-to-rt",
>  };
>  
>  static struct blkcg_policy ioprio_policy;
> @@ -189,6 +192,20 @@ void blkcg_set_ioprio(struct bio *bio)
>  	if (!blkcg || blkcg->prio_policy == POLICY_NO_CHANGE)
>  		return;
>  
> +	if (blkcg->prio_policy == POLICY_PROMOTE_TO_RT ||
> +	    blkcg->prio_policy == POLICY_NONE_TO_RT) {
> +		/*
> +		 * For RT threads, the default priority level is 4 because
> +		 * task_nice is 0. By promoting non-RT io-priority to RT-class
> +		 * and default level 4, those requests that are already
> +		 * RT-class but need a higher io-priority can use ioprio_set()
> +		 * to achieve this.
> +		 */
> +		if (IOPRIO_PRIO_CLASS(bio->bi_ioprio) != IOPRIO_CLASS_RT)
> +			bio->bi_ioprio = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_RT, 4);
> +		return;
> +	}
> +
>  	/*
>  	 * Except for IOPRIO_CLASS_NONE, higher I/O priority numbers
>  	 * correspond to a lower priority. Hence, the max_t() below selects
  

ping ?

On 5/8/2023 8:08 PM, Hou Tao wrote:
> ping ?
>
> On 4/28/2023 3:44 PM, Hou Tao wrote:
>> From: Hou Tao <houtao1@huawei.com>
>>
>> Since commit a78418e6a04c ("block: Always initialize bio IO priority on
>> submit"), bio->bi_ioprio will never be IOPRIO_CLASS_NONE when calling
>> blkcg_set_ioprio(), so there will be no way to promote the io-priority
>> of one cgroup to IOPRIO_CLASS_RT, because bi_ioprio will always be
>> greater than or equals to IOPRIO_CLASS_RT.
>>
>> It seems possible to call blkcg_set_ioprio() first then try to
>> initialize bi_ioprio later in bio_set_ioprio(), but this doesn't work
>> for bio in which bi_ioprio is already initialized (e.g., direct-io), so
>> introduce a new promote-to-rt policy to promote the iopriority of bio to
>> IOPRIO_CLASS_RT if the ioprio is not already RT.
>>
>> For none-to-rt policy, although it doesn't work now, but considering
>> that its purpose was also to override the io-priority to RT and allowing
>> for a smoother transition, just keep it and treat it as an alias of
>> the promote-to-rt policy.
>>
>> Acked-by: Tejun Heo <tj@kernel.org>
>> Reviewed-by: Bart Van Assche <bvanassche@acm.org>
>> Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
>> Reviewed-by: Jan Kara <jack@suse.cz>
>> Signed-off-by: Hou Tao <houtao1@huawei.com>
>> ---
>> v4:
>>  * rebased on 33afd4b76393
>>  * Add Reviewed-by from Jan Kara
>>
>> v3: https://lore.kernel.org/linux-block/20230223135154.3749088-1-houtao@huaweicloud.com
>>  * Use 'non-RT' instead of 'no-RT' in document (from Bagas)
>>  * Remove repeated sentence in commit message
>>  * Add Reviewed-by and Acked-by tags
>>  
>> v2: https://lore.kernel.org/linux-block/20230220135428.2632906-1-houtao@huaweicloud.com
>>
>>  * Simplify the implementation of promote-to-rt (from Bart)
>>  * Make none-to-rt to work again by treating it as an alias of
>>    the promote-to-rt policy (from Bart & Jan)
>>  * fix the style of new content in cgroup-v2.rst (from Bagas)
>>  * set the default priority level to 4 instead of 0 for promote-to-rt
>>
>> v1: https://lore.kernel.org/linux-block/20230201045227.2203123-1-houtao@huaweicloud.com
>>
>>  Documentation/admin-guide/cgroup-v2.rst | 42 ++++++++++++++-----------
>>  block/blk-ioprio.c                      | 23 ++++++++++++--
>>  2 files changed, 44 insertions(+), 21 deletions(-)
>>
>> diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
>> index f67c0829350b..7544ce00e0cb 100644
>> --- a/Documentation/admin-guide/cgroup-v2.rst
>> +++ b/Documentation/admin-guide/cgroup-v2.rst
>> @@ -2024,31 +2024,33 @@ 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 non-RT I/O priority class, change it into RT.
>> +	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:
>>  
>> @@ -2064,9 +2066,13 @@ 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
>>  ---
>> diff --git a/block/blk-ioprio.c b/block/blk-ioprio.c
>> index 055529b9b92b..4051fada01f1 100644
>> --- a/block/blk-ioprio.c
>> +++ b/block/blk-ioprio.c
>> @@ -23,25 +23,28 @@
>>  /**
>>   * enum prio_policy - I/O priority class policy.
>>   * @POLICY_NO_CHANGE: (default) do not modify the I/O priority class.
>> - * @POLICY_NONE_TO_RT: modify IOPRIO_CLASS_NONE into IOPRIO_CLASS_RT.
>> + * @POLICY_PROMOTE_TO_RT: modify no-IOPRIO_CLASS_RT to IOPRIO_CLASS_RT.
>>   * @POLICY_RESTRICT_TO_BE: modify IOPRIO_CLASS_NONE and IOPRIO_CLASS_RT into
>>   *		IOPRIO_CLASS_BE.
>>   * @POLICY_ALL_TO_IDLE: change the I/O priority class into IOPRIO_CLASS_IDLE.
>> + * @POLICY_NONE_TO_RT: an alias for POLICY_PROMOTE_TO_RT.
>>   *
>>   * See also <linux/ioprio.h>.
>>   */
>>  enum prio_policy {
>>  	POLICY_NO_CHANGE	= 0,
>> -	POLICY_NONE_TO_RT	= 1,
>> +	POLICY_PROMOTE_TO_RT	= 1,
>>  	POLICY_RESTRICT_TO_BE	= 2,
>>  	POLICY_ALL_TO_IDLE	= 3,
>> +	POLICY_NONE_TO_RT	= 4,
>>  };
>>  
>>  static const char *policy_name[] = {
>>  	[POLICY_NO_CHANGE]	= "no-change",
>> -	[POLICY_NONE_TO_RT]	= "none-to-rt",
>> +	[POLICY_PROMOTE_TO_RT]	= "promote-to-rt",
>>  	[POLICY_RESTRICT_TO_BE]	= "restrict-to-be",
>>  	[POLICY_ALL_TO_IDLE]	= "idle",
>> +	[POLICY_NONE_TO_RT]	= "none-to-rt",
>>  };
>>  
>>  static struct blkcg_policy ioprio_policy;
>> @@ -189,6 +192,20 @@ void blkcg_set_ioprio(struct bio *bio)
>>  	if (!blkcg || blkcg->prio_policy == POLICY_NO_CHANGE)
>>  		return;
>>  
>> +	if (blkcg->prio_policy == POLICY_PROMOTE_TO_RT ||
>> +	    blkcg->prio_policy == POLICY_NONE_TO_RT) {
>> +		/*
>> +		 * For RT threads, the default priority level is 4 because
>> +		 * task_nice is 0. By promoting non-RT io-priority to RT-class
>> +		 * and default level 4, those requests that are already
>> +		 * RT-class but need a higher io-priority can use ioprio_set()
>> +		 * to achieve this.
>> +		 */
>> +		if (IOPRIO_PRIO_CLASS(bio->bi_ioprio) != IOPRIO_CLASS_RT)
>> +			bio->bi_ioprio = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_RT, 4);
>> +		return;
>> +	}
>> +
>>  	/*
>>  	 * Except for IOPRIO_CLASS_NONE, higher I/O priority numbers
>>  	 * correspond to a lower priority. Hence, the max_t() below selects
> .
  

ping ?

On 5/23/2023 2:48 PM, Hou Tao wrote:
> ping ?
>
> On 5/8/2023 8:08 PM, Hou Tao wrote:
>> ping ?
>>
>> On 4/28/2023 3:44 PM, Hou Tao wrote:
>>> From: Hou Tao <houtao1@huawei.com>
>>>
>>> Since commit a78418e6a04c ("block: Always initialize bio IO priority on
>>> submit"), bio->bi_ioprio will never be IOPRIO_CLASS_NONE when calling
>>> blkcg_set_ioprio(), so there will be no way to promote the io-priority
>>> of one cgroup to IOPRIO_CLASS_RT, because bi_ioprio will always be
>>> greater than or equals to IOPRIO_CLASS_RT.
>>>
>>> It seems possible to call blkcg_set_ioprio() first then try to
>>> initialize bi_ioprio later in bio_set_ioprio(), but this doesn't work
>>> for bio in which bi_ioprio is already initialized (e.g., direct-io), so
>>> introduce a new promote-to-rt policy to promote the iopriority of bio to
>>> IOPRIO_CLASS_RT if the ioprio is not already RT.
>>>
>>> For none-to-rt policy, although it doesn't work now, but considering
>>> that its purpose was also to override the io-priority to RT and allowing
>>> for a smoother transition, just keep it and treat it as an alias of
>>> the promote-to-rt policy.
>>>
>>> Acked-by: Tejun Heo <tj@kernel.org>
>>> Reviewed-by: Bart Van Assche <bvanassche@acm.org>
>>> Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
>>> Reviewed-by: Jan Kara <jack@suse.cz>
>>> Signed-off-by: Hou Tao <houtao1@huawei.com>
>>> ---
>>> v4:
>>>  * rebased on 33afd4b76393
>>>  * Add Reviewed-by from Jan Kara
>>>
>>> v3: https://lore.kernel.org/linux-block/20230223135154.3749088-1-houtao@huaweicloud.com
>>>  * Use 'non-RT' instead of 'no-RT' in document (from Bagas)
>>>  * Remove repeated sentence in commit message
>>>  * Add Reviewed-by and Acked-by tags
>>>  
>>> v2: https://lore.kernel.org/linux-block/20230220135428.2632906-1-houtao@huaweicloud.com
>>>
>>>  * Simplify the implementation of promote-to-rt (from Bart)
>>>  * Make none-to-rt to work again by treating it as an alias of
>>>    the promote-to-rt policy (from Bart & Jan)
>>>  * fix the style of new content in cgroup-v2.rst (from Bagas)
>>>  * set the default priority level to 4 instead of 0 for promote-to-rt
>>>
>>> v1: https://lore.kernel.org/linux-block/20230201045227.2203123-1-houtao@huaweicloud.com
>>>
>>>  Documentation/admin-guide/cgroup-v2.rst | 42 ++++++++++++++-----------
>>>  block/blk-ioprio.c                      | 23 ++++++++++++--
>>>  2 files changed, 44 insertions(+), 21 deletions(-)
>>>
>>> diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
>>> index f67c0829350b..7544ce00e0cb 100644
>>> --- a/Documentation/admin-guide/cgroup-v2.rst
>>> +++ b/Documentation/admin-guide/cgroup-v2.rst
>>> @@ -2024,31 +2024,33 @@ 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 non-RT I/O priority class, change it into RT.
>>> +	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:
>>>  
>>> @@ -2064,9 +2066,13 @@ 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
>>>  ---
>>> diff --git a/block/blk-ioprio.c b/block/blk-ioprio.c
>>> index 055529b9b92b..4051fada01f1 100644
>>> --- a/block/blk-ioprio.c
>>> +++ b/block/blk-ioprio.c
>>> @@ -23,25 +23,28 @@
>>>  /**
>>>   * enum prio_policy - I/O priority class policy.
>>>   * @POLICY_NO_CHANGE: (default) do not modify the I/O priority class.
>>> - * @POLICY_NONE_TO_RT: modify IOPRIO_CLASS_NONE into IOPRIO_CLASS_RT.
>>> + * @POLICY_PROMOTE_TO_RT: modify no-IOPRIO_CLASS_RT to IOPRIO_CLASS_RT.
>>>   * @POLICY_RESTRICT_TO_BE: modify IOPRIO_CLASS_NONE and IOPRIO_CLASS_RT into
>>>   *		IOPRIO_CLASS_BE.
>>>   * @POLICY_ALL_TO_IDLE: change the I/O priority class into IOPRIO_CLASS_IDLE.
>>> + * @POLICY_NONE_TO_RT: an alias for POLICY_PROMOTE_TO_RT.
>>>   *
>>>   * See also <linux/ioprio.h>.
>>>   */
>>>  enum prio_policy {
>>>  	POLICY_NO_CHANGE	= 0,
>>> -	POLICY_NONE_TO_RT	= 1,
>>> +	POLICY_PROMOTE_TO_RT	= 1,
>>>  	POLICY_RESTRICT_TO_BE	= 2,
>>>  	POLICY_ALL_TO_IDLE	= 3,
>>> +	POLICY_NONE_TO_RT	= 4,
>>>  };
>>>  
>>>  static const char *policy_name[] = {
>>>  	[POLICY_NO_CHANGE]	= "no-change",
>>> -	[POLICY_NONE_TO_RT]	= "none-to-rt",
>>> +	[POLICY_PROMOTE_TO_RT]	= "promote-to-rt",
>>>  	[POLICY_RESTRICT_TO_BE]	= "restrict-to-be",
>>>  	[POLICY_ALL_TO_IDLE]	= "idle",
>>> +	[POLICY_NONE_TO_RT]	= "none-to-rt",
>>>  };
>>>  
>>>  static struct blkcg_policy ioprio_policy;
>>> @@ -189,6 +192,20 @@ void blkcg_set_ioprio(struct bio *bio)
>>>  	if (!blkcg || blkcg->prio_policy == POLICY_NO_CHANGE)
>>>  		return;
>>>  
>>> +	if (blkcg->prio_policy == POLICY_PROMOTE_TO_RT ||
>>> +	    blkcg->prio_policy == POLICY_NONE_TO_RT) {
>>> +		/*
>>> +		 * For RT threads, the default priority level is 4 because
>>> +		 * task_nice is 0. By promoting non-RT io-priority to RT-class
>>> +		 * and default level 4, those requests that are already
>>> +		 * RT-class but need a higher io-priority can use ioprio_set()
>>> +		 * to achieve this.
>>> +		 */
>>> +		if (IOPRIO_PRIO_CLASS(bio->bi_ioprio) != IOPRIO_CLASS_RT)
>>> +			bio->bi_ioprio = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_RT, 4);
>>> +		return;
>>> +	}
>>> +
>>>  	/*
>>>  	 * Except for IOPRIO_CLASS_NONE, higher I/O priority numbers
>>>  	 * correspond to a lower priority. Hence, the max_t() below selects
>> .
> .
  

On Fri, 28 Apr 2023 15:44:04 +0800, Hou Tao wrote:
> Since commit a78418e6a04c ("block: Always initialize bio IO priority on
> submit"), bio->bi_ioprio will never be IOPRIO_CLASS_NONE when calling
> blkcg_set_ioprio(), so there will be no way to promote the io-priority
> of one cgroup to IOPRIO_CLASS_RT, because bi_ioprio will always be
> greater than or equals to IOPRIO_CLASS_RT.
> 
> It seems possible to call blkcg_set_ioprio() first then try to
> initialize bi_ioprio later in bio_set_ioprio(), but this doesn't work
> for bio in which bi_ioprio is already initialized (e.g., direct-io), so
> introduce a new promote-to-rt policy to promote the iopriority of bio to
> IOPRIO_CLASS_RT if the ioprio is not already RT.
> 
> [...]

Applied, thanks!

[1/1] blk-ioprio: Introduce promote-to-rt policy
      commit: ddf63516d8d37528dc6834c7f19b55084e956068

Best regards,