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Message-ID: <1db53a95-46d3-c906-31a1-0be4992a4b8d@huaweicloud.com>
Date: Mon, 8 May 2023 20:08:15 +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 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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