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

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Date:   Fri, 3 Feb 2023 11:45:32 -0800
From:   Bart Van Assche <bvanassche@....org>
To:     Hou Tao <houtao@...weicloud.com>, linux-block@...r.kernel.org
Cc:     Jan Kara <jack@...e.cz>, Jens Axboe <axboe@...nel.dk>,
        cgroups@...r.kernel.org, Tejun Heo <tj@...nel.org>,
        Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Jonathan Corbet <corbet@....net>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, houtao1@...wei.com
Subject: Re: [PATCH] blk-ioprio: Introduce promote-to-rt policy

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)