[PATCH V2] null_blk: allow zero poll queues

[PATCH V2] null_blk: allow zero poll queues

[Ming Lei]

There isn't any reason to not allow zero poll queues from user
viewpoint.

Also sometimes we need to compare io poll between poll mode and irq
mode, so not allowing poll queues is bad.

Fixes: 15dfc662ef31 ("null_blk: Fix handling of submit_queues and poll_queues attributes")
Cc: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
V2:
	- fix divide zero fault as reported by Shin'ichiro

 drivers/block/null_blk/main.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/drivers/block/null_blk/main.c b/drivers/block/null_blk/main.c
index 54f7d490f8eb..c73e69ab77ed 100644
--- a/drivers/block/null_blk/main.c
+++ b/drivers/block/null_blk/main.c
@@ -340,9 +340,9 @@ static int nullb_update_nr_hw_queues(struct nullb_device *dev,
 		return 0;
 
 	/*
-	 * Make sure at least one queue exists for each of submit and poll.
+	 * Make sure at least one submit queue exists.
 	 */
-	if (!submit_queues || !poll_queues)
+	if (!submit_queues)
 		return -EINVAL;
 
 	/*
@@ -1878,8 +1878,7 @@ static int null_init_tag_set(struct nullb *nullb, struct blk_mq_tag_set *set)
 	set->nr_hw_queues = nullb ? nullb->dev->submit_queues :
 						g_submit_queues;
 	poll_queues = nullb ? nullb->dev->poll_queues : g_poll_queues;
-	if (poll_queues)
-		set->nr_hw_queues += poll_queues;
+	set->nr_hw_queues += poll_queues;
 	set->queue_depth = nullb ? nullb->dev->hw_queue_depth :
 						g_hw_queue_depth;
 	set->numa_node = nullb ? nullb->dev->home_node : g_home_node;
@@ -1890,7 +1889,7 @@ static int null_init_tag_set(struct nullb *nullb, struct blk_mq_tag_set *set)
 	if (g_shared_tag_bitmap)
 		set->flags |= BLK_MQ_F_TAG_HCTX_SHARED;
 	set->driver_data = nullb;
-	if (g_poll_queues)
+	if (poll_queues)
 		set->nr_maps = 3;
 	else
 		set->nr_maps = 1;
@@ -1917,8 +1916,6 @@ static int null_validate_conf(struct nullb_device *dev)
 
 	if (dev->poll_queues > g_poll_queues)
 		dev->poll_queues = g_poll_queues;
-	else if (dev->poll_queues == 0)
-		dev->poll_queues = 1;
 	dev->prev_poll_queues = dev->poll_queues;
 
 	dev->queue_mode = min_t(unsigned int, dev->queue_mode, NULL_Q_MQ);
-- 
2.31.1

Re: [PATCH V2] null_blk: allow zero poll queues

[Shinichiro Kawasaki]

On Dec 03, 2021 / 21:09, Ming Lei wrote:
> There isn't any reason to not allow zero poll queues from user
> viewpoint.
> 
> Also sometimes we need to compare io poll between poll mode and irq
> mode, so not allowing poll queues is bad.
> 
> Fixes: 15dfc662ef31 ("null_blk: Fix handling of submit_queues and poll_queues attributes")
> Cc: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
> Signed-off-by: Ming Lei <ming.lei@redhat.com>

Thank you for the fix. Looks good to me.

Reviewed-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>

-- 
Best Regards,
Shin'ichiro Kawasaki

Re: [PATCH V2] null_blk: allow zero poll queues

[Shinichiro Kawasaki]

On Dec 03, 2021 / 21:09, Ming Lei wrote:
> There isn't any reason to not allow zero poll queues from user
> viewpoint.
> 
> Also sometimes we need to compare io poll between poll mode and irq
> mode, so not allowing poll queues is bad.
> 
> Fixes: 15dfc662ef31 ("null_blk: Fix handling of submit_queues and poll_queues attributes")
> Cc: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> ---
> V2:
> 	- fix divide zero fault as reported by Shin'ichiro

Jens, Ming,

I find the V1 was applied to the for/5.17-drivers branch, and the additional fix
in the V2 does not look applied to the branch. Do we need another small patch to
cover the delta between V1 and V2?

-- 
Best Regards,
Shin'ichiro Kawasaki

Re: [PATCH V2] null_blk: allow zero poll queues

[Jens Axboe]

On 12/23/21 5:52 PM, Shinichiro Kawasaki wrote:
> On Dec 03, 2021 / 21:09, Ming Lei wrote:
>> There isn't any reason to not allow zero poll queues from user
>> viewpoint.
>>
>> Also sometimes we need to compare io poll between poll mode and irq
>> mode, so not allowing poll queues is bad.
>>
>> Fixes: 15dfc662ef31 ("null_blk: Fix handling of submit_queues and poll_queues attributes")
>> Cc: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
>> Signed-off-by: Ming Lei <ming.lei@redhat.com>
>> ---
>> V2:
>> 	- fix divide zero fault as reported by Shin'ichiro
> 
> Jens, Ming,
> 
> I find the V1 was applied to the for/5.17-drivers branch, and the additional fix
> in the V2 does not look applied to the branch. Do we need another small patch to
> cover the delta between V1 and V2?

Yes, please send an incremental, thanks.

-- 
Jens Axboe

Re: [PATCH V2] null_blk: allow zero poll queues

[Shinichiro Kawasaki]

On Dec 23, 2021 / 17:55, Jens Axboe wrote:
> On 12/23/21 5:52 PM, Shinichiro Kawasaki wrote:
> > On Dec 03, 2021 / 21:09, Ming Lei wrote:
> >> There isn't any reason to not allow zero poll queues from user
> >> viewpoint.
> >>
> >> Also sometimes we need to compare io poll between poll mode and irq
> >> mode, so not allowing poll queues is bad.
> >>
> >> Fixes: 15dfc662ef31 ("null_blk: Fix handling of submit_queues and poll_queues attributes")
> >> Cc: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
> >> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> >> ---
> >> V2:
> >> 	- fix divide zero fault as reported by Shin'ichiro
> > 
> > Jens, Ming,
> > 
> > I find the V1 was applied to the for/5.17-drivers branch, and the additional fix
> > in the V2 does not look applied to the branch. Do we need another small patch to
> > cover the delta between V1 and V2?
> 
> Yes, please send an incremental, thanks.

Thanks, and Ming already provided the small patch (So quick!). I've confirmed
that the patch avoids the issue. Merge to for/5.17-drivers will be appreciated.

-- 
Best Regards,
Shin'ichiro Kawasaki