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blk-ioprio: Introduce promote-to-rt policy

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Since commit a78418e6a0 ("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>
Reviewed-by: Bagas Sanjaya <bagasdotme@gmail.com>
Link: https://lore.kernel.org/r/20230428074404.280532-1-houtao@huaweicloud.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Hou Tao
2023-04-28 15:44:04 +08:00
committed by Jens Axboe
parent 8d21155467
commit ddf63516d8
2 changed files with 44 additions and 21 deletions
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23
block/blk-ioprio.c
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@@ -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