Commit ddf63516 authored by Hou Tao's avatar Hou Tao Committed by Jens Axboe

blk-ioprio: Introduce promote-to-rt policy

Since commit a78418e6 ("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: default avatarTejun Heo <tj@kernel.org>
Reviewed-by: default avatarBart Van Assche <bvanassche@acm.org>
Reviewed-by: default avatarChaitanya Kulkarni <kch@nvidia.com>
Reviewed-by: default avatarJan Kara <jack@suse.cz>
Signed-off-by: default avatarHou Tao <houtao1@huawei.com>
Reviewed-by: default avatarBagas Sanjaya <bagasdotme@gmail.com>
Link: https://lore.kernel.org/r/20230428074404.280532-1-houtao@huaweicloud.comSigned-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 8d211554
...@@ -2024,31 +2024,33 @@ that attribute: ...@@ -2024,31 +2024,33 @@ that attribute:
no-change no-change
Do not modify the I/O priority class. Do not modify the I/O priority class.
none-to-rt promote-to-rt
For requests that do not have an I/O priority class (NONE), For requests that have a non-RT I/O priority class, change it into RT.
change the I/O priority class into RT. Do not modify Also change the priority level of these requests to 4. Do not modify
the I/O priority class of other requests. the I/O priority of requests that have priority class RT.
restrict-to-be restrict-to-be
For requests that do not have an I/O priority class or that have I/O 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 priority class RT, change it into BE. Also change the priority level
class of requests that have priority class IDLE. of these requests to 0. Do not modify the I/O priority class of
requests that have priority class IDLE.
idle idle
Change the I/O priority class of all requests into IDLE, the lowest Change the I/O priority class of all requests into IDLE, the lowest
I/O priority class. 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: The following numerical values are associated with the I/O priority policies:
+-------------+---+ +----------------+---+
| no-change | 0 | | no-change | 0 |
+-------------+---+ +----------------+---+
| none-to-rt | 1 | | rt-to-be | 2 |
+-------------+---+ +----------------+---+
| rt-to-be | 2 | | all-to-idle | 3 |
+-------------+---+ +----------------+---+
| all-to-idle | 3 |
+-------------+---+
The numerical value that corresponds to each I/O priority class is as follows: 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: ...@@ -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: 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. - If I/O priority class policy is promote-to-rt, change the request I/O
- Change the request I/O priority class into the maximum of the I/O priority priority class to IOPRIO_CLASS_RT and change the request I/O priority
class policy number and the numerical I/O priority class. 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 PID
--- ---
......
...@@ -23,25 +23,28 @@ ...@@ -23,25 +23,28 @@
/** /**
* enum prio_policy - I/O priority class policy. * enum prio_policy - I/O priority class policy.
* @POLICY_NO_CHANGE: (default) do not modify the I/O priority class. * @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 * @POLICY_RESTRICT_TO_BE: modify IOPRIO_CLASS_NONE and IOPRIO_CLASS_RT into
* IOPRIO_CLASS_BE. * IOPRIO_CLASS_BE.
* @POLICY_ALL_TO_IDLE: change the I/O priority class into IOPRIO_CLASS_IDLE. * @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>. * See also <linux/ioprio.h>.
*/ */
enum prio_policy { enum prio_policy {
POLICY_NO_CHANGE = 0, POLICY_NO_CHANGE = 0,
POLICY_NONE_TO_RT = 1, POLICY_PROMOTE_TO_RT = 1,
POLICY_RESTRICT_TO_BE = 2, POLICY_RESTRICT_TO_BE = 2,
POLICY_ALL_TO_IDLE = 3, POLICY_ALL_TO_IDLE = 3,
POLICY_NONE_TO_RT = 4,
}; };
static const char *policy_name[] = { static const char *policy_name[] = {
[POLICY_NO_CHANGE] = "no-change", [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_RESTRICT_TO_BE] = "restrict-to-be",
[POLICY_ALL_TO_IDLE] = "idle", [POLICY_ALL_TO_IDLE] = "idle",
[POLICY_NONE_TO_RT] = "none-to-rt",
}; };
static struct blkcg_policy ioprio_policy; static struct blkcg_policy ioprio_policy;
...@@ -189,6 +192,20 @@ void blkcg_set_ioprio(struct bio *bio) ...@@ -189,6 +192,20 @@ void blkcg_set_ioprio(struct bio *bio)
if (!blkcg || blkcg->prio_policy == POLICY_NO_CHANGE) if (!blkcg || blkcg->prio_policy == POLICY_NO_CHANGE)
return; 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 * Except for IOPRIO_CLASS_NONE, higher I/O priority numbers
* correspond to a lower priority. Hence, the max_t() below selects * correspond to a lower priority. Hence, the max_t() below selects
......
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