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Message-ID: <bff92f4c-0f21-9cf2-7135-812a184716b3@huaweicloud.com>
Date: Tue, 23 May 2023 14:48:20 +0800
From: Hou Tao <houtao@...weicloud.com>
To: linux-block@...r.kernel.org, Jens Axboe <axboe@...nel.dk>
Cc: Bart Van Assche <bvanassche@....org>, Jan Kara <jack@...e.cz>,
Bagas Sanjaya <bagasdotme@...il.com>,
Chaitanya Kulkarni <kch@...dia.com>, 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" <houtao1@...wei.com>
Subject: Re: [PATCH v4] blk-ioprio: Introduce promote-to-rt policy
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@...wei.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@...nel.org>
>> Reviewed-by: Bart Van Assche <bvanassche@....org>
>> Reviewed-by: Chaitanya Kulkarni <kch@...dia.com>
>> Reviewed-by: Jan Kara <jack@...e.cz>
>> Signed-off-by: Hou Tao <houtao1@...wei.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
> .
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