blk-wbt: don't enable throttling if default elevator is bfq

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@huawei.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20221019121518.3865235-7-yukuai1@huaweicloud.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 7ea4278..ccfadc6 100644 (file)
--- 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 07ed0b0..68a774d 100644 (file)
--- 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 ed574bf..7538247 100644 (file)
--- 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