[PATCH 0/4] blk-throttle cleanups

[PATCH 0/4] blk-throttle cleanups

[Yu Kuai]

From: Yu Kuai <yukuai3@huawei.com>

There are no functional changes.

Yu Kuai (4):
  blk-throttle: use 'READ/WRITE' instead of '0/1'
  blk-throttle: calling throtl_dequeue/enqueue_tg in pairs
  blk-throttle: cleanup tg_update_disptime()
  blk-throttle: cleanup throtl_dequeue_tg()

 block/blk-throttle.c | 24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

-- 
2.31.1

[PATCH 1/4] blk-throttle: use 'READ/WRITE' instead of '0/1'

[Yu Kuai]

From: Yu Kuai <yukuai3@huawei.com>

Make the code easier to read, like everywhere else.

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Acked-by: Tejun Heo <tj@kernel.org>
---
 block/blk-throttle.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 9f5fe62afff9..fe1fa6441105 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -329,8 +329,8 @@ static struct bio *throtl_pop_queued(struct list_head *queued,
 /* init a service_queue, assumes the caller zeroed it */
 static void throtl_service_queue_init(struct throtl_service_queue *sq)
 {
-	INIT_LIST_HEAD(&sq->queued[0]);
-	INIT_LIST_HEAD(&sq->queued[1]);
+	INIT_LIST_HEAD(&sq->queued[READ]);
+	INIT_LIST_HEAD(&sq->queued[WRITE]);
 	sq->pending_tree = RB_ROOT_CACHED;
 	timer_setup(&sq->pending_timer, throtl_pending_timer_fn, 0);
 }
@@ -1106,7 +1106,7 @@ static int throtl_select_dispatch(struct throtl_service_queue *parent_sq)
 		nr_disp += throtl_dispatch_tg(tg);
 
 		sq = &tg->service_queue;
-		if (sq->nr_queued[0] || sq->nr_queued[1])
+		if (sq->nr_queued[READ] || sq->nr_queued[WRITE])
 			tg_update_disptime(tg);
 
 		if (nr_disp >= THROTL_QUANTUM)
-- 
2.31.1

[PATCH 2/4] blk-throttle: calling throtl_dequeue/enqueue_tg in pairs

[Yu Kuai]

From: Yu Kuai <yukuai3@huawei.com>

It's a little weird to call throtl_dequeue_tg() unconditionally in
throtl_select_dispatch(), since it will be called in tg_update_disptime()
again if some bio is still throttled. Thus call it later if there are no
throttled bio. There are no functional changes.

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Acked-by: Tejun Heo <tj@kernel.org>
---
 block/blk-throttle.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index fe1fa6441105..64002435fa43 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -1101,13 +1101,13 @@ static int throtl_select_dispatch(struct throtl_service_queue *parent_sq)
 		if (time_before(jiffies, tg->disptime))
 			break;
 
-		throtl_dequeue_tg(tg);
-
 		nr_disp += throtl_dispatch_tg(tg);
 
 		sq = &tg->service_queue;
 		if (sq->nr_queued[READ] || sq->nr_queued[WRITE])
 			tg_update_disptime(tg);
+		else
+			throtl_dequeue_tg(tg);
 
 		if (nr_disp >= THROTL_QUANTUM)
 			break;
-- 
2.31.1

[PATCH 3/4] blk-throttle: cleanup tg_update_disptime()

[Yu Kuai]

From: Yu Kuai <yukuai3@huawei.com>

tg_update_disptime() only need to adjust postion for 'tg' in
'parent_sq', there is no need to call throtl_enqueue/dequeue_tg(),
since they will set/clear flag THROTL_TG_PENDING and increase/decrease
nr_pending, which is useless. By the way, clear the flag/decrease
nr_pending while there are still throttled bios is not good for debugging.

There are no functional changes.

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
---
 block/blk-throttle.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 64002435fa43..47142a1dd102 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -520,7 +520,6 @@ static void throtl_rb_erase(struct rb_node *n,
 {
 	rb_erase_cached(n, &parent_sq->pending_tree);
 	RB_CLEAR_NODE(n);
-	--parent_sq->nr_pending;
 }
 
 static void update_min_dispatch_time(struct throtl_service_queue *parent_sq)
@@ -572,7 +571,11 @@ static void throtl_enqueue_tg(struct throtl_grp *tg)
 static void throtl_dequeue_tg(struct throtl_grp *tg)
 {
 	if (tg->flags & THROTL_TG_PENDING) {
-		throtl_rb_erase(&tg->rb_node, tg->service_queue.parent_sq);
+		struct throtl_service_queue *parent_sq =
+			tg->service_queue.parent_sq;
+
+		throtl_rb_erase(&tg->rb_node, parent_sq);
+		--parent_sq->nr_pending;
 		tg->flags &= ~THROTL_TG_PENDING;
 	}
 }
@@ -990,9 +993,9 @@ static void tg_update_disptime(struct throtl_grp *tg)
 	disptime = jiffies + min_wait;
 
 	/* Update dispatch time */
-	throtl_dequeue_tg(tg);
+	throtl_rb_erase(&tg->rb_node, tg->service_queue.parent_sq);
 	tg->disptime = disptime;
-	throtl_enqueue_tg(tg);
+	tg_service_queue_add(tg);
 
 	/* see throtl_add_bio_tg() */
 	tg->flags &= ~THROTL_TG_WAS_EMPTY;
-- 
2.31.1

[PATCH 4/4] blk-throttle: cleanup throtl_dequeue_tg()

[Yu Kuai]

From: Yu Kuai <yukuai3@huawei.com>

Now that throtl_dequeue_tg() is called when the last bio is dispatched,
there is no need to check the flag THROTL_TG_PENDING, since it's ensured
to be set when bio is throttled.

There are no functional changes.

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
---
 block/blk-throttle.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 47142a1dd102..e47506a8ef47 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -570,14 +570,11 @@ static void throtl_enqueue_tg(struct throtl_grp *tg)
 
 static void throtl_dequeue_tg(struct throtl_grp *tg)
 {
-	if (tg->flags & THROTL_TG_PENDING) {
-		struct throtl_service_queue *parent_sq =
-			tg->service_queue.parent_sq;
+	struct throtl_service_queue *parent_sq = tg->service_queue.parent_sq;
 
-		throtl_rb_erase(&tg->rb_node, parent_sq);
-		--parent_sq->nr_pending;
-		tg->flags &= ~THROTL_TG_PENDING;
-	}
+	throtl_rb_erase(&tg->rb_node, parent_sq);
+	--parent_sq->nr_pending;
+	tg->flags &= ~THROTL_TG_PENDING;
 }
 
 /* Call with queue lock held */
-- 
2.31.1

Re: [PATCH 3/4] blk-throttle: cleanup tg_update_disptime()

[Tejun Heo]

On Tue, Aug 23, 2022 at 09:38:09AM +0800, Yu Kuai wrote:
> From: Yu Kuai <yukuai3@huawei.com>
> 
> tg_update_disptime() only need to adjust postion for 'tg' in
> 'parent_sq', there is no need to call throtl_enqueue/dequeue_tg(),
> since they will set/clear flag THROTL_TG_PENDING and increase/decrease
> nr_pending, which is useless. By the way, clear the flag/decrease
> nr_pending while there are still throttled bios is not good for debugging.
> 
> There are no functional changes.
> 
> Signed-off-by: Yu Kuai <yukuai3@huawei.com>

Acked-by: Tejun Heo <tj@kernel.org>

Thanks.

-- 
tejun

Re: [PATCH 4/4] blk-throttle: cleanup throtl_dequeue_tg()

[Tejun Heo]

On Tue, Aug 23, 2022 at 09:38:10AM +0800, Yu Kuai wrote:
> From: Yu Kuai <yukuai3@huawei.com>
> 
> Now that throtl_dequeue_tg() is called when the last bio is dispatched,
> there is no need to check the flag THROTL_TG_PENDING, since it's ensured
> to be set when bio is throttled.
> 
> There are no functional changes.
> 
> Signed-off-by: Yu Kuai <yukuai3@huawei.com>
> ---
>  block/blk-throttle.c | 11 ++++-------
>  1 file changed, 4 insertions(+), 7 deletions(-)
> 
> diff --git a/block/blk-throttle.c b/block/blk-throttle.c
> index 47142a1dd102..e47506a8ef47 100644
> --- a/block/blk-throttle.c
> +++ b/block/blk-throttle.c
> @@ -570,14 +570,11 @@ static void throtl_enqueue_tg(struct throtl_grp *tg)
>  
>  static void throtl_dequeue_tg(struct throtl_grp *tg)
>  {
> -	if (tg->flags & THROTL_TG_PENDING) {
> -		struct throtl_service_queue *parent_sq =
> -			tg->service_queue.parent_sq;
> +	struct throtl_service_queue *parent_sq = tg->service_queue.parent_sq;
>  
> -		throtl_rb_erase(&tg->rb_node, parent_sq);
> -		--parent_sq->nr_pending;
> -		tg->flags &= ~THROTL_TG_PENDING;
> -	}
> +	throtl_rb_erase(&tg->rb_node, parent_sq);
> +	--parent_sq->nr_pending;
> +	tg->flags &= ~THROTL_TG_PENDING;

Yeah, I don't know about this one. This breaks the symmetry with
throtl_enqueue_tg() and it's a bit odd that we aren't at least
WARN_ON_ONCE() on the flag given what the flag tracks. If you want to do
this, I think the prev approach of just removing the flag is better as that
was symmetric at least.

Thanks.

-- 
tejun

Re: [PATCH 4/4] blk-throttle: cleanup throtl_dequeue_tg()

[Yu Kuai]

Hi, Tejun

在 2022/08/24 2:34, Tejun Heo 写道:
> On Tue, Aug 23, 2022 at 09:38:10AM +0800, Yu Kuai wrote:
>> From: Yu Kuai <yukuai3@huawei.com>
>>
>> Now that throtl_dequeue_tg() is called when the last bio is dispatched,
>> there is no need to check the flag THROTL_TG_PENDING, since it's ensured
>> to be set when bio is throttled.
>>
>> There are no functional changes.
>>
>> Signed-off-by: Yu Kuai <yukuai3@huawei.com>
>> ---
>>   block/blk-throttle.c | 11 ++++-------
>>   1 file changed, 4 insertions(+), 7 deletions(-)
>>
>> diff --git a/block/blk-throttle.c b/block/blk-throttle.c
>> index 47142a1dd102..e47506a8ef47 100644
>> --- a/block/blk-throttle.c
>> +++ b/block/blk-throttle.c
>> @@ -570,14 +570,11 @@ static void throtl_enqueue_tg(struct throtl_grp *tg)
>>   
>>   static void throtl_dequeue_tg(struct throtl_grp *tg)
>>   {
>> -	if (tg->flags & THROTL_TG_PENDING) {
>> -		struct throtl_service_queue *parent_sq =
>> -			tg->service_queue.parent_sq;
>> +	struct throtl_service_queue *parent_sq = tg->service_queue.parent_sq;
>>   
>> -		throtl_rb_erase(&tg->rb_node, parent_sq);
>> -		--parent_sq->nr_pending;
>> -		tg->flags &= ~THROTL_TG_PENDING;
>> -	}
>> +	throtl_rb_erase(&tg->rb_node, parent_sq);
>> +	--parent_sq->nr_pending;
>> +	tg->flags &= ~THROTL_TG_PENDING;
> 
> Yeah, I don't know about this one. This breaks the symmetry with
> throtl_enqueue_tg() and it's a bit odd that we aren't at least
> WARN_ON_ONCE() on the flag given what the flag tracks. If you want to do
> this, I think the prev approach of just removing the flag is better as that
> was symmetric at least.

Yes, you are right, thanks for the advice. Since now it's a bit
ambivalent, we might as well just remove this patch?

Thanks,
Kuai
> 
> Thanks.
>