From ddf63516d8d37528dc6834c7f19b55084e956068 Mon Sep 17 00:00:00 2001 From: Hou Tao Date: Fri, 28 Apr 2023 15:44:04 +0800 Subject: [PATCH] blk-ioprio: Introduce promote-to-rt policy 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 Reviewed-by: Bart Van Assche Reviewed-by: Chaitanya Kulkarni Reviewed-by: Jan Kara Signed-off-by: Hou Tao Reviewed-by: Bagas Sanjaya Link: https://lore.kernel.org/r/20230428074404.280532-1-houtao@huaweicloud.com Signed-off-by: Jens Axboe --- 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 . */ 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