Re: [PATCH] blk-ioprio: Introduce promote-to-rt policy

Bart Van Assche
2023-02-03T19:45:32Z

On 2/2/23 17:48, Hou Tao wrote:
> I don't get it on how to remove IOPRIO_POL_PROMOTION when calculating the final
> ioprio for bio. IOPRIO_POL_PROMOTION is not used for IOPRIO_CLASS values but
> used to determinate on how to calculate the final ioprio for bio: choosing the
> maximum or minimum between blkcg ioprio and original bio bi_ioprio.

Do the block layer code changes shown below implement the functionality that you
need?

Thanks,

Bart.

diff --git a/block/blk-ioprio.c b/block/blk-ioprio.c
index 8bb6b8eba4ce..4a56da95168e 100644
--- a/block/blk-ioprio.c
+++ b/block/blk-ioprio.c
@@ -27,6 +27,8 @@
* @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_PROMOTE_TO_RT: modify IOPRIO_CLASS_NONE and IOPRIO_CLASS_BE into
+ * IOPRIO_CLASS_RT.
*
* See also <linux/ioprio.h>.
*/
@@ -35,6 +37,7 @@ enum prio_policy {
POLICY_NONE_TO_RT = 1,
POLICY_RESTRICT_TO_BE = 2,
POLICY_ALL_TO_IDLE = 3,
+ POLICY_PROMOTE_TO_RT,
};

static const char *policy_name[] = {
@@ -42,6 +45,7 @@ static const char *policy_name[] = {
[POLICY_NONE_TO_RT] = "none-to-rt",
[POLICY_RESTRICT_TO_BE] = "restrict-to-be",
[POLICY_ALL_TO_IDLE] = "idle",
+ [POLICY_PROMOTE_TO_RT] = "promote-to-rt",
};

static struct blkcg_policy ioprio_policy;
@@ -189,17 +193,23 @@ void blkcg_set_ioprio(struct bio *bio)
if (!blkcg || blkcg->prio_policy == POLICY_NO_CHANGE)
return;

- /*
- * Except for IOPRIO_CLASS_NONE, higher I/O priority numbers
- * correspond to a lower priority. Hence, the max_t() below selects
- * the lower priority of bi_ioprio and the cgroup I/O priority class.
- * If the bio I/O priority equals IOPRIO_CLASS_NONE, the cgroup I/O
- * priority is assigned to the bio.
- */
- prio = max_t(u16, bio->bi_ioprio,
- IOPRIO_PRIO_VALUE(blkcg->prio_policy, 0));
- if (prio > bio->bi_ioprio)
- bio->bi_ioprio = prio;
+ if (blkcg->prio_policy == PROMOTE_TO_RT) {
+ if (IOPRIO_PRIO_CLASS(bio->bi_ioprio) != IOPRIO_CLASS_RT)
+ bio->bi_ioprio = IOPRIO_CLASS_RT;
+ } else {
+ /*
+ * Except for IOPRIO_CLASS_NONE, higher I/O priority numbers
+ * correspond to a lower priority. Hence, the max_t() below
+ * selects the lower priority of bi_ioprio and the cgroup I/O
+ * priority class. If the bio I/O priority equals
+ * IOPRIO_CLASS_NONE, the cgroup I/O priority is assigned to the
+ * bio.
+ */
+ prio = max_t(u16, bio->bi_ioprio,
+ IOPRIO_PRIO_VALUE(blkcg->prio_policy, 0));
+ if (prio > bio->bi_ioprio)
+ bio->bi_ioprio = prio;
+ }
}

void blk_ioprio_exit(struct gendisk *disk)