linux-kernel - [PATCH v4 6/6] blk-wbt: don't enable throttling if default elevator is bfq

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Date:   Fri, 30 Sep 2022 11:19:06 +0800
From:   Yu Kuai <yukuai1@...weicloud.com>
To:     jack@...e.cz, hch@...radead.org, ebiggers@...nel.org,
        paolo.valente@...aro.org, axboe@...nel.dk
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        yukuai3@...wei.com, yukuai1@...weicloud.com, yi.zhang@...wei.com
Subject: [PATCH v4 6/6] blk-wbt: don't enable throttling if default elevator is bfq

From: Yu Kuai <yukuai3@...wei.com>

Commit b5dc5d4d1f4f ("block,bfq: Disable writeback throttling") tries to
disable wbt for bfq, it's done by calling wbt_disable_default() in
bfq_init_queue(). However, wbt is still enabled if default elevator is
bfq:

device_add_disk
 elevator_init_mq
  bfq_init_queue
   wbt_disable_default -> done nothing

 blk_register_queue
  wbt_enable_default -> wbt is enabled

Fix the problem by adding a new flag ELEVATOR_FLAG_DISBALE_WBT, bfq
will set the flag in bfq_init_queue, and following wbt_enable_default()
won't enable wbt while the flag is set.

Signed-off-by: Yu Kuai <yukuai3@...wei.com>
---
 block/bfq-iosched.c |  2 ++
 block/blk-wbt.c     | 11 ++++++++---
 block/elevator.h    |  3 ++-
 3 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 7ea427817f7f..ccfadc6f71bf 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -7045,6 +7045,7 @@ static void bfq_exit_queue(struct elevator_queue *e)
 #endif
 
 	blk_stat_disable_accounting(bfqd->queue);
+	clear_bit(ELEVATOR_FLAG_DISABLE_WBT, &e->flags);
 	wbt_enable_default(bfqd->queue);
 
 	kfree(bfqd);
@@ -7190,6 +7191,7 @@ static int bfq_init_queue(struct request_queue *q, struct elevator_type *e)
 	/* We dispatch from request queue wide instead of hw queue */
 	blk_queue_flag_set(QUEUE_FLAG_SQ_SCHED, q);
 
+	set_bit(ELEVATOR_FLAG_DISABLE_WBT, &eq->flags);
 	wbt_disable_default(q);
 	blk_stat_enable_accounting(q);
 
diff --git a/block/blk-wbt.c b/block/blk-wbt.c
index 1852ef223c68..41f5aae659f0 100644
--- a/block/blk-wbt.c
+++ b/block/blk-wbt.c
@@ -27,6 +27,7 @@
 
 #include "blk-wbt.h"
 #include "blk-rq-qos.h"
+#include "elevator.h"
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/wbt.h>
@@ -651,11 +652,15 @@ void wbt_set_write_cache(struct request_queue *q, bool write_cache_on)
  */
 void wbt_enable_default(struct request_queue *q)
 {
-	struct rq_qos *rqos = wbt_rq_qos(q);
+	struct rq_qos *rqos;
+	bool disable_flag = q->elevator &&
+		    test_bit(ELEVATOR_FLAG_DISABLE_WBT, &q->elevator->flags);
 
 	/* Throttling already enabled? */
+	rqos = wbt_rq_qos(q);
 	if (rqos) {
-		if (RQWB(rqos)->enable_state == WBT_STATE_OFF_DEFAULT)
+		if (!disable_flag &&
+		    RQWB(rqos)->enable_state == WBT_STATE_OFF_DEFAULT)
 			RQWB(rqos)->enable_state = WBT_STATE_ON_DEFAULT;
 		return;
 	}
@@ -664,7 +669,7 @@ void wbt_enable_default(struct request_queue *q)
 	if (!blk_queue_registered(q))
 		return;
 
-	if (queue_is_mq(q))
+	if (queue_is_mq(q) && !disable_flag)
 		wbt_init(q);
 }
 EXPORT_SYMBOL_GPL(wbt_enable_default);
diff --git a/block/elevator.h b/block/elevator.h
index ed574bf3e629..75382471222d 100644
--- a/block/elevator.h
+++ b/block/elevator.h
@@ -104,7 +104,8 @@ struct elevator_queue
 	DECLARE_HASHTABLE(hash, ELV_HASH_BITS);
 };
 
-#define ELEVATOR_FLAG_REGISTERED 0
+#define ELEVATOR_FLAG_REGISTERED	0
+#define ELEVATOR_FLAG_DISABLE_WBT	1
 
 /*
  * block elevator interface
-- 
2.31.1