linux-kernel - [RFC PATCH 8/8] bfq: optimize the calculation of bfq_weight_to

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Message-Id: <cbd1e689ca0010c3d437f22c904f10b123e6b1f4.1615203034.git.brookxu@tencent.com>
Date:   Mon,  8 Mar 2021 20:00:21 +0800
From:   brookxu <brookxu.cn@...il.com>
To:     paolo.valente@...aro.org, axboe@...nel.dk, tj@...nel.org
Cc:     linux-block@...r.kernel.org, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [RFC PATCH 8/8] bfq: optimize the calculation of bfq_weight_to_ioprio()

From: Chunguang Xu <brookxu@...cent.com>

From: Chunguang Xu <brookxu@...cent.com>

The value range of ioprio is [0, 7], but the result of
bfq_weight_to_ioprio() may exceed this range, so simple
optimization is required.

Signed-off-by: Chunguang Xu <brookxu@...cent.com>
---
 block/bfq-wf2q.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/block/bfq-wf2q.c b/block/bfq-wf2q.c
index 850a8e2f0bda..1d565daf516f 100644
--- a/block/bfq-wf2q.c
+++ b/block/bfq-wf2q.c
@@ -536,8 +536,9 @@ unsigned short bfq_ioprio_to_weight(int ioprio)
  */
 static unsigned short bfq_weight_to_ioprio(int weight)
 {
-	return max_t(int, 0,
-		     IOPRIO_BE_NR * BFQ_WEIGHT_CONVERSION_COEFF - weight);
+	int ioprio = IOPRIO_BE_NR  - weight / BFQ_WEIGHT_CONVERSION_COEFF;
+
+	return ioprio < 0 ? 0 : min_t(int, ioprio, IOPRIO_BE_NR - 1);
 }
 
 static void bfq_get_entity(struct bfq_entity *entity)
-- 
2.30.0