From: Hou Tao <houtao1@xxxxxxxxxx>
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 ioprio policy to promote the iopriority of bio to
IOPRIO_CLASS_RT if the ioprio is not already RT.
So introduce a new promote-to-rt policy to achieve this. 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 allow for a smoother
transition, just keep it and treat it as an alias of the promote-to-rt
policy.
Signed-off-by: Hou Tao <houtao1@xxxxxxxxxx>
---
v2:
* 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@xxxxxxxxxxxxxxx
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 74cec76be9f2..ccfb9fdfbc16 100644
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -2021,31 +2021,33 @@ 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 no-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:
@@ -2061,9 +2063,13 @@ 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 8bb6b8eba4ce..4eba569d4823 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
--
2.29.2
