[v2,3/3] blk-wbt: don't enable throttling if default elevator is bfq

Commit Message

Yu Kuai Sept. 19, 2022, 7:09 a.m. UTC

From: Yu Kuai <[e-mail]>

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 checking elevator name if wbt_enable_default() is
called from blk_register_queue().

Signed-off-by: Yu Kuai <[e-mail]>
---
 block/bfq-iosched.c | 2 +-
 block/blk-sysfs.c   | 2 +-
 block/blk-wbt.c     | 6 +++++-
 block/blk-wbt.h     | 5 +++--
 4 files changed, 10 insertions(+), 5 deletions(-)

Comments

Christoph Hellwig Sept. 20, 2022, 7:25 a.m. UTC | #1

Matching names is always is a bad idea.

Just ad a flags field to elevator_mq_ops, add a DISABLE_WBT flag
to it, and check for that and everything should become much, much
simpler.

Yu Kuai Sept. 20, 2022, 7:48 a.m. UTC | #2

Hi, Christoph!

在 2022/09/20 15:25, Christoph Hellwig 写道:
> Matching names is always is a bad idea.
> 
> Just ad a flags field to elevator_mq_ops, add a DISABLE_WBT flag
> to it, and check for that and everything should become much, much
> simpler.

Thanks for the adivce, that is a good idea!

Kuai
> 
> .
>

Patch

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 7ea427817f7f..f769c90744fd 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -7045,7 +7045,7 @@  static void bfq_exit_queue(struct elevator_queue *e)
 #endif
 
 	blk_stat_disable_accounting(bfqd->queue);
-	wbt_enable_default(bfqd->queue);
+	wbt_enable_default(bfqd->queue, false);
 
 	kfree(bfqd);
 }
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 1955bb6a284d..3e8adb95ff02 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -850,7 +850,7 @@  int blk_register_queue(struct gendisk *disk)
 		goto put_dev;
 
 	blk_queue_flag_set(QUEUE_FLAG_REGISTERED, q);
-	wbt_enable_default(q);
+	wbt_enable_default(q, true);
 	blk_throtl_register_queue(q);
 
 	/* Now everything is ready and send out KOBJ_ADD uevent */
diff --git a/block/blk-wbt.c b/block/blk-wbt.c
index 68851c2c02d2..c6256e7c9e8e 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>
@@ -643,10 +644,13 @@  void wbt_set_write_cache(struct request_queue *q, bool write_cache_on)
 /*
  * Enable wbt if defaults are configured that way
  */
-void wbt_enable_default(struct request_queue *q)
+void wbt_enable_default(struct request_queue *q, bool check_elevator)
 {
 	struct rq_qos *rqos = wbt_rq_qos(q);
 
+	if (check_elevator && check_elevator_name(q->elevator, "bfq"))
+		return;
+
 	/* Throttling already enabled? */
 	if (rqos) {
 		if (RQWB(rqos)->enable_state == WBT_STATE_OFF_DEFAULT)
diff --git a/block/blk-wbt.h b/block/blk-wbt.h
index e42465ddcbb6..eb028febaff0 100644
--- a/block/blk-wbt.h
+++ b/block/blk-wbt.h
@@ -90,7 +90,7 @@  static inline unsigned int wbt_inflight(struct rq_wb *rwb)
 
 int wbt_init(struct request_queue *);
 void wbt_disable_default(struct request_queue *);
-void wbt_enable_default(struct request_queue *);
+void wbt_enable_default(struct request_queue *, bool);
 
 u64 wbt_get_min_lat(struct request_queue *q);
 void wbt_set_min_lat(struct request_queue *q, u64 val);
@@ -109,7 +109,8 @@  static inline int wbt_init(struct request_queue *q)
 static inline void wbt_disable_default(struct request_queue *q)
 {
 }
-static inline void wbt_enable_default(struct request_queue *q)
+static inline void wbt_enable_default(struct request_queue *q,
+				      bool check_elevator)
 {
 }
 static inline void wbt_set_write_cache(struct request_queue *q, bool wc)