Re: [PATCH v2 02/15] blk-ioprio: Modify fewer bio->bi_ioprio bits

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On 10/5/23 23:36, Kanchan Joshi wrote:
On Thu, Oct 05, 2023 at 12:40:48PM -0700, Bart Van Assche wrote:
A later patch will store the data lifetime in the bio->bi_ioprio member
before the blk-ioprio policy is applied. Make sure that this policy doesn't
clear more bits than necessary.

Cc: Damien Le Moal <dlemoal@xxxxxxxxxx>
Cc: Niklas Cassel <niklas.cassel@xxxxxxx>
Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
---
block/blk-ioprio.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/block/blk-ioprio.c b/block/blk-ioprio.c
index 4051fada01f1..2db86f153b6d 100644
--- a/block/blk-ioprio.c
+++ b/block/blk-ioprio.c
@@ -202,7 +202,8 @@ void blkcg_set_ioprio(struct bio *bio)
         * to achieve this.
         */
        if (IOPRIO_PRIO_CLASS(bio->bi_ioprio) != IOPRIO_CLASS_RT)
-            bio->bi_ioprio = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_RT, 4);
+            ioprio_set_class_and_level(&bio->bi_ioprio,
+                    IOPRIO_PRIO_VALUE(IOPRIO_CLASS_RT, 4));
        return;
    }

@@ -213,10 +214,10 @@ void blkcg_set_ioprio(struct bio *bio)
     * 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,
+    prio = max_t(u16, bio->bi_ioprio & IOPRIO_CLASS_LEVEL_MASK,
            IOPRIO_PRIO_VALUE(blkcg->prio_policy, 0));

All 9 bits (including CDL) are not taking part in this decision making
now. Maybe you want to exclude only lifetime bits.

-    if (prio > bio->bi_ioprio)
-        bio->bi_ioprio = prio;
+    if (prio > (bio->bi_ioprio & IOPRIO_CLASS_LEVEL_MASK))
+        ioprio_set_class_and_level(&bio->bi_ioprio, prio);

Same as above.

Hi Kanchan,

It is intentional that the CDL bits are left out from these decisions.
I think the decisions made in this policy should be based on the I/O
priority class and level only and not on the CDL value.

Thanks,

Bart.



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