[PATCH v2 1/1] virtio-blk: add num_io_queues module parameter

[PATCH v2 1/1] virtio-blk: add num_io_queues module parameter

[Max Gurtovoy]

Sometimes a user would like to control the amount of IO queues to be
created for a block device. For example, for limiting the memory
footprint of virtio-blk devices.

Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
---

changes from v1:
 - use param_set_uint_minmax (from Christoph)
 - added "Should > 0" to module description

Note: This commit apply on top of Jens's branch for-5.15/drivers
---
 drivers/block/virtio_blk.c | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 4b49df2dfd23..9332fc4e9b31 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -24,6 +24,22 @@
 /* The maximum number of sg elements that fit into a virtqueue */
 #define VIRTIO_BLK_MAX_SG_ELEMS 32768
 
+static int virtblk_queue_count_set(const char *val,
+		const struct kernel_param *kp)
+{
+	return param_set_uint_minmax(val, kp, 1, nr_cpu_ids);
+}
+
+static const struct kernel_param_ops queue_count_ops = {
+	.set = virtblk_queue_count_set,
+	.get = param_get_uint,
+};
+
+static unsigned int num_io_queues;
+module_param_cb(num_io_queues, &queue_count_ops, &num_io_queues, 0644);
+MODULE_PARM_DESC(num_io_queues,
+		 "Number of IO virt queues to use for blk device. Should > 0");
+
 static int major;
 static DEFINE_IDA(vd_index_ida);
 
@@ -501,7 +517,9 @@ static int init_vq(struct virtio_blk *vblk)
 	if (err)
 		num_vqs = 1;
 
-	num_vqs = min_t(unsigned int, nr_cpu_ids, num_vqs);
+	num_vqs = min_t(unsigned int,
+			min_not_zero(num_io_queues, nr_cpu_ids),
+			num_vqs);
 
 	vblk->vqs = kmalloc_array(num_vqs, sizeof(*vblk->vqs), GFP_KERNEL);
 	if (!vblk->vqs)
-- 
2.18.1

Re: [PATCH v2 1/1] virtio-blk: add num_io_queues module parameter

[Christoph Hellwig]

Looks good,

Reviewed-by: Christoph Hellwig <hch@lst.de>

Re: [PATCH v2 1/1] virtio-blk: add num_io_queues module parameter

[Christoph Hellwig]

Looks good,

Reviewed-by: Christoph Hellwig <hch@lst.de>
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Re: [PATCH v2 1/1] virtio-blk: add num_io_queues module parameter

[Stefan Hajnoczi]

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On Tue, Aug 31, 2021 at 04:50:35PM +0300, Max Gurtovoy wrote:
> Sometimes a user would like to control the amount of IO queues to be
> created for a block device. For example, for limiting the memory
> footprint of virtio-blk devices.
> 
> Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
> ---
> 
> changes from v1:
>  - use param_set_uint_minmax (from Christoph)
>  - added "Should > 0" to module description
> 
> Note: This commit apply on top of Jens's branch for-5.15/drivers
> ---
>  drivers/block/virtio_blk.c | 20 +++++++++++++++++++-
>  1 file changed, 19 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index 4b49df2dfd23..9332fc4e9b31 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -24,6 +24,22 @@
>  /* The maximum number of sg elements that fit into a virtqueue */
>  #define VIRTIO_BLK_MAX_SG_ELEMS 32768
>  
> +static int virtblk_queue_count_set(const char *val,
> +		const struct kernel_param *kp)
> +{
> +	return param_set_uint_minmax(val, kp, 1, nr_cpu_ids);
> +}
> +
> +static const struct kernel_param_ops queue_count_ops = {
> +	.set = virtblk_queue_count_set,
> +	.get = param_get_uint,
> +};
> +
> +static unsigned int num_io_queues;
> +module_param_cb(num_io_queues, &queue_count_ops, &num_io_queues, 0644);
> +MODULE_PARM_DESC(num_io_queues,
> +		 "Number of IO virt queues to use for blk device. Should > 0");
> +
>  static int major;
>  static DEFINE_IDA(vd_index_ida);
>  
> @@ -501,7 +517,9 @@ static int init_vq(struct virtio_blk *vblk)
>  	if (err)
>  		num_vqs = 1;
>  
> -	num_vqs = min_t(unsigned int, nr_cpu_ids, num_vqs);
> +	num_vqs = min_t(unsigned int,
> +			min_not_zero(num_io_queues, nr_cpu_ids),
> +			num_vqs);

If you respin, please consider calling them request queues. That's the
terminology from the VIRTIO spec and it's nice to keep it consistent.
But the purpose of num_io_queues is clear, so:

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

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Re: [PATCH v2 1/1] virtio-blk: add num_io_queues module parameter

[Stefan Hajnoczi]

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On Tue, Aug 31, 2021 at 04:50:35PM +0300, Max Gurtovoy wrote:
> Sometimes a user would like to control the amount of IO queues to be
> created for a block device. For example, for limiting the memory
> footprint of virtio-blk devices.
> 
> Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
> ---
> 
> changes from v1:
>  - use param_set_uint_minmax (from Christoph)
>  - added "Should > 0" to module description
> 
> Note: This commit apply on top of Jens's branch for-5.15/drivers
> ---
>  drivers/block/virtio_blk.c | 20 +++++++++++++++++++-
>  1 file changed, 19 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index 4b49df2dfd23..9332fc4e9b31 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -24,6 +24,22 @@
>  /* The maximum number of sg elements that fit into a virtqueue */
>  #define VIRTIO_BLK_MAX_SG_ELEMS 32768
>  
> +static int virtblk_queue_count_set(const char *val,
> +		const struct kernel_param *kp)
> +{
> +	return param_set_uint_minmax(val, kp, 1, nr_cpu_ids);
> +}
> +
> +static const struct kernel_param_ops queue_count_ops = {
> +	.set = virtblk_queue_count_set,
> +	.get = param_get_uint,
> +};
> +
> +static unsigned int num_io_queues;
> +module_param_cb(num_io_queues, &queue_count_ops, &num_io_queues, 0644);
> +MODULE_PARM_DESC(num_io_queues,
> +		 "Number of IO virt queues to use for blk device. Should > 0");
> +
>  static int major;
>  static DEFINE_IDA(vd_index_ida);
>  
> @@ -501,7 +517,9 @@ static int init_vq(struct virtio_blk *vblk)
>  	if (err)
>  		num_vqs = 1;
>  
> -	num_vqs = min_t(unsigned int, nr_cpu_ids, num_vqs);
> +	num_vqs = min_t(unsigned int,
> +			min_not_zero(num_io_queues, nr_cpu_ids),
> +			num_vqs);

If you respin, please consider calling them request queues. That's the
terminology from the VIRTIO spec and it's nice to keep it consistent.
But the purpose of num_io_queues is clear, so:

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

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Re: [PATCH v2 1/1] virtio-blk: add num_io_queues module parameter

[Michael S. Tsirkin]

On Thu, Sep 02, 2021 at 02:45:52PM +0100, Stefan Hajnoczi wrote:
> On Tue, Aug 31, 2021 at 04:50:35PM +0300, Max Gurtovoy wrote:
> > Sometimes a user would like to control the amount of IO queues to be
> > created for a block device. For example, for limiting the memory
> > footprint of virtio-blk devices.
> > 
> > Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
> > ---
> > 
> > changes from v1:
> >  - use param_set_uint_minmax (from Christoph)
> >  - added "Should > 0" to module description
> > 
> > Note: This commit apply on top of Jens's branch for-5.15/drivers
> > ---
> >  drivers/block/virtio_blk.c | 20 +++++++++++++++++++-
> >  1 file changed, 19 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> > index 4b49df2dfd23..9332fc4e9b31 100644
> > --- a/drivers/block/virtio_blk.c
> > +++ b/drivers/block/virtio_blk.c
> > @@ -24,6 +24,22 @@
> >  /* The maximum number of sg elements that fit into a virtqueue */
> >  #define VIRTIO_BLK_MAX_SG_ELEMS 32768
> >  
> > +static int virtblk_queue_count_set(const char *val,
> > +		const struct kernel_param *kp)
> > +{
> > +	return param_set_uint_minmax(val, kp, 1, nr_cpu_ids);
> > +}
> > +
> > +static const struct kernel_param_ops queue_count_ops = {
> > +	.set = virtblk_queue_count_set,
> > +	.get = param_get_uint,
> > +};
> > +
> > +static unsigned int num_io_queues;
> > +module_param_cb(num_io_queues, &queue_count_ops, &num_io_queues, 0644);
> > +MODULE_PARM_DESC(num_io_queues,
> > +		 "Number of IO virt queues to use for blk device. Should > 0");
> > +
> >  static int major;
> >  static DEFINE_IDA(vd_index_ida);
> >  
> > @@ -501,7 +517,9 @@ static int init_vq(struct virtio_blk *vblk)
> >  	if (err)
> >  		num_vqs = 1;
> >  
> > -	num_vqs = min_t(unsigned int, nr_cpu_ids, num_vqs);
> > +	num_vqs = min_t(unsigned int,
> > +			min_not_zero(num_io_queues, nr_cpu_ids),
> > +			num_vqs);
> 
> If you respin, please consider calling them request queues. That's the
> terminology from the VIRTIO spec and it's nice to keep it consistent.
> But the purpose of num_io_queues is clear, so:
> 
> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

I did this:
+static unsigned int num_io_request_queues;
+module_param_cb(num_io_request_queues, &queue_count_ops, &num_io_request_queues, 0644);
+MODULE_PARM_DESC(num_io_request_queues,
+                "Limit number of IO request virt queues to use for each device. 0 for now limit");

Re: [PATCH v2 1/1] virtio-blk: add num_io_queues module parameter

[Michael S. Tsirkin]

On Thu, Sep 02, 2021 at 02:45:52PM +0100, Stefan Hajnoczi wrote:
> On Tue, Aug 31, 2021 at 04:50:35PM +0300, Max Gurtovoy wrote:
> > Sometimes a user would like to control the amount of IO queues to be
> > created for a block device. For example, for limiting the memory
> > footprint of virtio-blk devices.
> > 
> > Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
> > ---
> > 
> > changes from v1:
> >  - use param_set_uint_minmax (from Christoph)
> >  - added "Should > 0" to module description
> > 
> > Note: This commit apply on top of Jens's branch for-5.15/drivers
> > ---
> >  drivers/block/virtio_blk.c | 20 +++++++++++++++++++-
> >  1 file changed, 19 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> > index 4b49df2dfd23..9332fc4e9b31 100644
> > --- a/drivers/block/virtio_blk.c
> > +++ b/drivers/block/virtio_blk.c
> > @@ -24,6 +24,22 @@
> >  /* The maximum number of sg elements that fit into a virtqueue */
> >  #define VIRTIO_BLK_MAX_SG_ELEMS 32768
> >  
> > +static int virtblk_queue_count_set(const char *val,
> > +		const struct kernel_param *kp)
> > +{
> > +	return param_set_uint_minmax(val, kp, 1, nr_cpu_ids);
> > +}
> > +
> > +static const struct kernel_param_ops queue_count_ops = {
> > +	.set = virtblk_queue_count_set,
> > +	.get = param_get_uint,
> > +};
> > +
> > +static unsigned int num_io_queues;
> > +module_param_cb(num_io_queues, &queue_count_ops, &num_io_queues, 0644);
> > +MODULE_PARM_DESC(num_io_queues,
> > +		 "Number of IO virt queues to use for blk device. Should > 0");
> > +
> >  static int major;
> >  static DEFINE_IDA(vd_index_ida);
> >  
> > @@ -501,7 +517,9 @@ static int init_vq(struct virtio_blk *vblk)
> >  	if (err)
> >  		num_vqs = 1;
> >  
> > -	num_vqs = min_t(unsigned int, nr_cpu_ids, num_vqs);
> > +	num_vqs = min_t(unsigned int,
> > +			min_not_zero(num_io_queues, nr_cpu_ids),
> > +			num_vqs);
> 
> If you respin, please consider calling them request queues. That's the
> terminology from the VIRTIO spec and it's nice to keep it consistent.
> But the purpose of num_io_queues is clear, so:
> 
> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

I did this:
+static unsigned int num_io_request_queues;
+module_param_cb(num_io_request_queues, &queue_count_ops, &num_io_request_queues, 0644);
+MODULE_PARM_DESC(num_io_request_queues,
+                "Limit number of IO request virt queues to use for each device. 0 for now limit");

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Re: [PATCH v2 1/1] virtio-blk: add num_io_queues module parameter

[Max Gurtovoy]

On 9/5/2021 7:02 PM, Michael S. Tsirkin wrote:
> On Thu, Sep 02, 2021 at 02:45:52PM +0100, Stefan Hajnoczi wrote:
>> On Tue, Aug 31, 2021 at 04:50:35PM +0300, Max Gurtovoy wrote:
>>> Sometimes a user would like to control the amount of IO queues to be
>>> created for a block device. For example, for limiting the memory
>>> footprint of virtio-blk devices.
>>>
>>> Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
>>> ---
>>>
>>> changes from v1:
>>>   - use param_set_uint_minmax (from Christoph)
>>>   - added "Should > 0" to module description
>>>
>>> Note: This commit apply on top of Jens's branch for-5.15/drivers
>>> ---
>>>   drivers/block/virtio_blk.c | 20 +++++++++++++++++++-
>>>   1 file changed, 19 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
>>> index 4b49df2dfd23..9332fc4e9b31 100644
>>> --- a/drivers/block/virtio_blk.c
>>> +++ b/drivers/block/virtio_blk.c
>>> @@ -24,6 +24,22 @@
>>>   /* The maximum number of sg elements that fit into a virtqueue */
>>>   #define VIRTIO_BLK_MAX_SG_ELEMS 32768
>>>   
>>> +static int virtblk_queue_count_set(const char *val,
>>> +		const struct kernel_param *kp)
>>> +{
>>> +	return param_set_uint_minmax(val, kp, 1, nr_cpu_ids);
>>> +}
>>> +
>>> +static const struct kernel_param_ops queue_count_ops = {
>>> +	.set = virtblk_queue_count_set,
>>> +	.get = param_get_uint,
>>> +};
>>> +
>>> +static unsigned int num_io_queues;
>>> +module_param_cb(num_io_queues, &queue_count_ops, &num_io_queues, 0644);
>>> +MODULE_PARM_DESC(num_io_queues,
>>> +		 "Number of IO virt queues to use for blk device. Should > 0");
>>> +
>>>   static int major;
>>>   static DEFINE_IDA(vd_index_ida);
>>>   
>>> @@ -501,7 +517,9 @@ static int init_vq(struct virtio_blk *vblk)
>>>   	if (err)
>>>   		num_vqs = 1;
>>>   
>>> -	num_vqs = min_t(unsigned int, nr_cpu_ids, num_vqs);
>>> +	num_vqs = min_t(unsigned int,
>>> +			min_not_zero(num_io_queues, nr_cpu_ids),
>>> +			num_vqs);
>> If you respin, please consider calling them request queues. That's the
>> terminology from the VIRTIO spec and it's nice to keep it consistent.
>> But the purpose of num_io_queues is clear, so:
>>
>> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> I did this:
> +static unsigned int num_io_request_queues;
> +module_param_cb(num_io_request_queues, &queue_count_ops, &num_io_request_queues, 0644);
> +MODULE_PARM_DESC(num_io_request_queues,
> +                "Limit number of IO request virt queues to use for each device. 0 for now limit");

The parameter is writable and can be changed and then new devices might 
be probed with new value.

It can't be zero in the code. we can change param_set_uint_minmax args 
and say that 0 says nr_cpus.

I'm ok with the renaming but I prefer to stick to the description we 
gave in V3 of this patch (and maybe enable value of 0 as mentioned above).

Re: [PATCH v2 1/1] virtio-blk: add num_io_queues module parameter

[Michael S. Tsirkin]

On Mon, Sep 06, 2021 at 01:31:32AM +0300, Max Gurtovoy wrote:
> 
> On 9/5/2021 7:02 PM, Michael S. Tsirkin wrote:
> > On Thu, Sep 02, 2021 at 02:45:52PM +0100, Stefan Hajnoczi wrote:
> > > On Tue, Aug 31, 2021 at 04:50:35PM +0300, Max Gurtovoy wrote:
> > > > Sometimes a user would like to control the amount of IO queues to be
> > > > created for a block device. For example, for limiting the memory
> > > > footprint of virtio-blk devices.
> > > > 
> > > > Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
> > > > ---
> > > > 
> > > > changes from v1:
> > > >   - use param_set_uint_minmax (from Christoph)
> > > >   - added "Should > 0" to module description
> > > > 
> > > > Note: This commit apply on top of Jens's branch for-5.15/drivers
> > > > ---
> > > >   drivers/block/virtio_blk.c | 20 +++++++++++++++++++-
> > > >   1 file changed, 19 insertions(+), 1 deletion(-)
> > > > 
> > > > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> > > > index 4b49df2dfd23..9332fc4e9b31 100644
> > > > --- a/drivers/block/virtio_blk.c
> > > > +++ b/drivers/block/virtio_blk.c
> > > > @@ -24,6 +24,22 @@
> > > >   /* The maximum number of sg elements that fit into a virtqueue */
> > > >   #define VIRTIO_BLK_MAX_SG_ELEMS 32768
> > > > +static int virtblk_queue_count_set(const char *val,
> > > > +		const struct kernel_param *kp)
> > > > +{
> > > > +	return param_set_uint_minmax(val, kp, 1, nr_cpu_ids);
> > > > +}


Hmm which tree is this for?

> > > > +
> > > > +static const struct kernel_param_ops queue_count_ops = {
> > > > +	.set = virtblk_queue_count_set,
> > > > +	.get = param_get_uint,
> > > > +};
> > > > +
> > > > +static unsigned int num_io_queues;
> > > > +module_param_cb(num_io_queues, &queue_count_ops, &num_io_queues, 0644);
> > > > +MODULE_PARM_DESC(num_io_queues,
> > > > +		 "Number of IO virt queues to use for blk device. Should > 0");



better:

+MODULE_PARM_DESC(num_io_request_queues,
+                "Limit number of IO request virt queues to use for each device. 0 for now limit");


> > > > +
> > > >   static int major;
> > > >   static DEFINE_IDA(vd_index_ida);
> > > > @@ -501,7 +517,9 @@ static int init_vq(struct virtio_blk *vblk)
> > > >   	if (err)
> > > >   		num_vqs = 1;
> > > > -	num_vqs = min_t(unsigned int, nr_cpu_ids, num_vqs);
> > > > +	num_vqs = min_t(unsigned int,
> > > > +			min_not_zero(num_io_queues, nr_cpu_ids),
> > > > +			num_vqs);
> > > If you respin, please consider calling them request queues. That's the
> > > terminology from the VIRTIO spec and it's nice to keep it consistent.
> > > But the purpose of num_io_queues is clear, so:
> > > 
> > > Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> > I did this:
> > +static unsigned int num_io_request_queues;
> > +module_param_cb(num_io_request_queues, &queue_count_ops, &num_io_request_queues, 0644);
> > +MODULE_PARM_DESC(num_io_request_queues,
> > +                "Limit number of IO request virt queues to use for each device. 0 for now limit");
> 
> The parameter is writable and can be changed and then new devices might be
> probed with new value.
> 
> It can't be zero in the code. we can change param_set_uint_minmax args and
> say that 0 says nr_cpus.
> 
> I'm ok with the renaming but I prefer to stick to the description we gave in
> V3 of this patch (and maybe enable value of 0 as mentioned above).

Re: [PATCH v2 1/1] virtio-blk: add num_io_queues module parameter

[Michael S. Tsirkin]

On Mon, Sep 06, 2021 at 01:31:32AM +0300, Max Gurtovoy wrote:
> 
> On 9/5/2021 7:02 PM, Michael S. Tsirkin wrote:
> > On Thu, Sep 02, 2021 at 02:45:52PM +0100, Stefan Hajnoczi wrote:
> > > On Tue, Aug 31, 2021 at 04:50:35PM +0300, Max Gurtovoy wrote:
> > > > Sometimes a user would like to control the amount of IO queues to be
> > > > created for a block device. For example, for limiting the memory
> > > > footprint of virtio-blk devices.
> > > > 
> > > > Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
> > > > ---
> > > > 
> > > > changes from v1:
> > > >   - use param_set_uint_minmax (from Christoph)
> > > >   - added "Should > 0" to module description
> > > > 
> > > > Note: This commit apply on top of Jens's branch for-5.15/drivers
> > > > ---
> > > >   drivers/block/virtio_blk.c | 20 +++++++++++++++++++-
> > > >   1 file changed, 19 insertions(+), 1 deletion(-)
> > > > 
> > > > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> > > > index 4b49df2dfd23..9332fc4e9b31 100644
> > > > --- a/drivers/block/virtio_blk.c
> > > > +++ b/drivers/block/virtio_blk.c
> > > > @@ -24,6 +24,22 @@
> > > >   /* The maximum number of sg elements that fit into a virtqueue */
> > > >   #define VIRTIO_BLK_MAX_SG_ELEMS 32768
> > > > +static int virtblk_queue_count_set(const char *val,
> > > > +		const struct kernel_param *kp)
> > > > +{
> > > > +	return param_set_uint_minmax(val, kp, 1, nr_cpu_ids);
> > > > +}


Hmm which tree is this for?

> > > > +
> > > > +static const struct kernel_param_ops queue_count_ops = {
> > > > +	.set = virtblk_queue_count_set,
> > > > +	.get = param_get_uint,
> > > > +};
> > > > +
> > > > +static unsigned int num_io_queues;
> > > > +module_param_cb(num_io_queues, &queue_count_ops, &num_io_queues, 0644);
> > > > +MODULE_PARM_DESC(num_io_queues,
> > > > +		 "Number of IO virt queues to use for blk device. Should > 0");



better:

+MODULE_PARM_DESC(num_io_request_queues,
+                "Limit number of IO request virt queues to use for each device. 0 for now limit");


> > > > +
> > > >   static int major;
> > > >   static DEFINE_IDA(vd_index_ida);
> > > > @@ -501,7 +517,9 @@ static int init_vq(struct virtio_blk *vblk)
> > > >   	if (err)
> > > >   		num_vqs = 1;
> > > > -	num_vqs = min_t(unsigned int, nr_cpu_ids, num_vqs);
> > > > +	num_vqs = min_t(unsigned int,
> > > > +			min_not_zero(num_io_queues, nr_cpu_ids),
> > > > +			num_vqs);
> > > If you respin, please consider calling them request queues. That's the
> > > terminology from the VIRTIO spec and it's nice to keep it consistent.
> > > But the purpose of num_io_queues is clear, so:
> > > 
> > > Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> > I did this:
> > +static unsigned int num_io_request_queues;
> > +module_param_cb(num_io_request_queues, &queue_count_ops, &num_io_request_queues, 0644);
> > +MODULE_PARM_DESC(num_io_request_queues,
> > +                "Limit number of IO request virt queues to use for each device. 0 for now limit");
> 
> The parameter is writable and can be changed and then new devices might be
> probed with new value.
> 
> It can't be zero in the code. we can change param_set_uint_minmax args and
> say that 0 says nr_cpus.
> 
> I'm ok with the renaming but I prefer to stick to the description we gave in
> V3 of this patch (and maybe enable value of 0 as mentioned above).

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Re: [PATCH v2 1/1] virtio-blk: add num_io_queues module parameter

[Max Gurtovoy]

On 9/6/2021 2:20 PM, Michael S. Tsirkin wrote:
> On Mon, Sep 06, 2021 at 01:31:32AM +0300, Max Gurtovoy wrote:
>> On 9/5/2021 7:02 PM, Michael S. Tsirkin wrote:
>>> On Thu, Sep 02, 2021 at 02:45:52PM +0100, Stefan Hajnoczi wrote:
>>>> On Tue, Aug 31, 2021 at 04:50:35PM +0300, Max Gurtovoy wrote:
>>>>> Sometimes a user would like to control the amount of IO queues to be
>>>>> created for a block device. For example, for limiting the memory
>>>>> footprint of virtio-blk devices.
>>>>>
>>>>> Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
>>>>> ---
>>>>>
>>>>> changes from v1:
>>>>>    - use param_set_uint_minmax (from Christoph)
>>>>>    - added "Should > 0" to module description
>>>>>
>>>>> Note: This commit apply on top of Jens's branch for-5.15/drivers
>>>>> ---
>>>>>    drivers/block/virtio_blk.c | 20 +++++++++++++++++++-
>>>>>    1 file changed, 19 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
>>>>> index 4b49df2dfd23..9332fc4e9b31 100644
>>>>> --- a/drivers/block/virtio_blk.c
>>>>> +++ b/drivers/block/virtio_blk.c
>>>>> @@ -24,6 +24,22 @@
>>>>>    /* The maximum number of sg elements that fit into a virtqueue */
>>>>>    #define VIRTIO_BLK_MAX_SG_ELEMS 32768
>>>>> +static int virtblk_queue_count_set(const char *val,
>>>>> +		const struct kernel_param *kp)
>>>>> +{
>>>>> +	return param_set_uint_minmax(val, kp, 1, nr_cpu_ids);
>>>>> +}
>
> Hmm which tree is this for?

I've mentioned in the note that it apply on branch for-5.15/drivers. But 
now you can apply it on linus/master as well.


>
>>>>> +
>>>>> +static const struct kernel_param_ops queue_count_ops = {
>>>>> +	.set = virtblk_queue_count_set,
>>>>> +	.get = param_get_uint,
>>>>> +};
>>>>> +
>>>>> +static unsigned int num_io_queues;
>>>>> +module_param_cb(num_io_queues, &queue_count_ops, &num_io_queues, 0644);
>>>>> +MODULE_PARM_DESC(num_io_queues,
>>>>> +		 "Number of IO virt queues to use for blk device. Should > 0");
>
>
> better:
>
> +MODULE_PARM_DESC(num_io_request_queues,
> +                "Limit number of IO request virt queues to use for each device. 0 for now limit");

You proposed it and I replied on it bellow.


>
>
>>>>> +
>>>>>    static int major;
>>>>>    static DEFINE_IDA(vd_index_ida);
>>>>> @@ -501,7 +517,9 @@ static int init_vq(struct virtio_blk *vblk)
>>>>>    	if (err)
>>>>>    		num_vqs = 1;
>>>>> -	num_vqs = min_t(unsigned int, nr_cpu_ids, num_vqs);
>>>>> +	num_vqs = min_t(unsigned int,
>>>>> +			min_not_zero(num_io_queues, nr_cpu_ids),
>>>>> +			num_vqs);
>>>> If you respin, please consider calling them request queues. That's the
>>>> terminology from the VIRTIO spec and it's nice to keep it consistent.
>>>> But the purpose of num_io_queues is clear, so:
>>>>
>>>> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
>>> I did this:
>>> +static unsigned int num_io_request_queues;
>>> +module_param_cb(num_io_request_queues, &queue_count_ops, &num_io_request_queues, 0644);
>>> +MODULE_PARM_DESC(num_io_request_queues,
>>> +                "Limit number of IO request virt queues to use for each device. 0 for now limit");
>> The parameter is writable and can be changed and then new devices might be
>> probed with new value.
>>
>> It can't be zero in the code. we can change param_set_uint_minmax args and
>> say that 0 says nr_cpus.
>>
>> I'm ok with the renaming but I prefer to stick to the description we gave in
>> V3 of this patch (and maybe enable value of 0 as mentioned above).

Re: [PATCH v2 1/1] virtio-blk: add num_io_queues module parameter

[Michael S. Tsirkin]

On Mon, Sep 06, 2021 at 02:59:40PM +0300, Max Gurtovoy wrote:
> 
> On 9/6/2021 2:20 PM, Michael S. Tsirkin wrote:
> > On Mon, Sep 06, 2021 at 01:31:32AM +0300, Max Gurtovoy wrote:
> > > On 9/5/2021 7:02 PM, Michael S. Tsirkin wrote:
> > > > On Thu, Sep 02, 2021 at 02:45:52PM +0100, Stefan Hajnoczi wrote:
> > > > > On Tue, Aug 31, 2021 at 04:50:35PM +0300, Max Gurtovoy wrote:
> > > > > > Sometimes a user would like to control the amount of IO queues to be
> > > > > > created for a block device. For example, for limiting the memory
> > > > > > footprint of virtio-blk devices.
> > > > > > 
> > > > > > Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
> > > > > > ---
> > > > > > 
> > > > > > changes from v1:
> > > > > >    - use param_set_uint_minmax (from Christoph)
> > > > > >    - added "Should > 0" to module description
> > > > > > 
> > > > > > Note: This commit apply on top of Jens's branch for-5.15/drivers
> > > > > > ---
> > > > > >    drivers/block/virtio_blk.c | 20 +++++++++++++++++++-
> > > > > >    1 file changed, 19 insertions(+), 1 deletion(-)
> > > > > > 
> > > > > > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> > > > > > index 4b49df2dfd23..9332fc4e9b31 100644
> > > > > > --- a/drivers/block/virtio_blk.c
> > > > > > +++ b/drivers/block/virtio_blk.c
> > > > > > @@ -24,6 +24,22 @@
> > > > > >    /* The maximum number of sg elements that fit into a virtqueue */
> > > > > >    #define VIRTIO_BLK_MAX_SG_ELEMS 32768
> > > > > > +static int virtblk_queue_count_set(const char *val,
> > > > > > +		const struct kernel_param *kp)
> > > > > > +{
> > > > > > +	return param_set_uint_minmax(val, kp, 1, nr_cpu_ids);
> > > > > > +}
> > 
> > Hmm which tree is this for?
> 
> I've mentioned in the note that it apply on branch for-5.15/drivers. But now
> you can apply it on linus/master as well.
> 
> 
> > 
> > > > > > +
> > > > > > +static const struct kernel_param_ops queue_count_ops = {
> > > > > > +	.set = virtblk_queue_count_set,
> > > > > > +	.get = param_get_uint,
> > > > > > +};
> > > > > > +
> > > > > > +static unsigned int num_io_queues;
> > > > > > +module_param_cb(num_io_queues, &queue_count_ops, &num_io_queues, 0644);
> > > > > > +MODULE_PARM_DESC(num_io_queues,
> > > > > > +		 "Number of IO virt queues to use for blk device. Should > 0");
> > 
> > 
> > better:
> > 
> > +MODULE_PARM_DESC(num_io_request_queues,
> > +                "Limit number of IO request virt queues to use for each device. 0 for now limit");
> 
> You proposed it and I replied on it bellow.


Can't say I understand 100% what you are saying. Want to send
a description that does make sense to you but
also reflects reality? 0 is the default so
"should > 0" besides being ungrammatical does not seem t"
reflect what it does ...

> 
> > 
> > 
> > > > > > +
> > > > > >    static int major;
> > > > > >    static DEFINE_IDA(vd_index_ida);
> > > > > > @@ -501,7 +517,9 @@ static int init_vq(struct virtio_blk *vblk)
> > > > > >    	if (err)
> > > > > >    		num_vqs = 1;
> > > > > > -	num_vqs = min_t(unsigned int, nr_cpu_ids, num_vqs);
> > > > > > +	num_vqs = min_t(unsigned int,
> > > > > > +			min_not_zero(num_io_queues, nr_cpu_ids),
> > > > > > +			num_vqs);
> > > > > If you respin, please consider calling them request queues. That's the
> > > > > terminology from the VIRTIO spec and it's nice to keep it consistent.
> > > > > But the purpose of num_io_queues is clear, so:
> > > > > 
> > > > > Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> > > > I did this:
> > > > +static unsigned int num_io_request_queues;
> > > > +module_param_cb(num_io_request_queues, &queue_count_ops, &num_io_request_queues, 0644);
> > > > +MODULE_PARM_DESC(num_io_request_queues,
> > > > +                "Limit number of IO request virt queues to use for each device. 0 for now limit");
> > > The parameter is writable and can be changed and then new devices might be
> > > probed with new value.
> > > 
> > > It can't be zero in the code. we can change param_set_uint_minmax args and
> > > say that 0 says nr_cpus.
> > > 
> > > I'm ok with the renaming but I prefer to stick to the description we gave in
> > > V3 of this patch (and maybe enable value of 0 as mentioned above).

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Re: [PATCH v2 1/1] virtio-blk: add num_io_queues module parameter

[Michael S. Tsirkin]

On Mon, Sep 06, 2021 at 02:59:40PM +0300, Max Gurtovoy wrote:
> 
> On 9/6/2021 2:20 PM, Michael S. Tsirkin wrote:
> > On Mon, Sep 06, 2021 at 01:31:32AM +0300, Max Gurtovoy wrote:
> > > On 9/5/2021 7:02 PM, Michael S. Tsirkin wrote:
> > > > On Thu, Sep 02, 2021 at 02:45:52PM +0100, Stefan Hajnoczi wrote:
> > > > > On Tue, Aug 31, 2021 at 04:50:35PM +0300, Max Gurtovoy wrote:
> > > > > > Sometimes a user would like to control the amount of IO queues to be
> > > > > > created for a block device. For example, for limiting the memory
> > > > > > footprint of virtio-blk devices.
> > > > > > 
> > > > > > Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
> > > > > > ---
> > > > > > 
> > > > > > changes from v1:
> > > > > >    - use param_set_uint_minmax (from Christoph)
> > > > > >    - added "Should > 0" to module description
> > > > > > 
> > > > > > Note: This commit apply on top of Jens's branch for-5.15/drivers
> > > > > > ---
> > > > > >    drivers/block/virtio_blk.c | 20 +++++++++++++++++++-
> > > > > >    1 file changed, 19 insertions(+), 1 deletion(-)
> > > > > > 
> > > > > > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> > > > > > index 4b49df2dfd23..9332fc4e9b31 100644
> > > > > > --- a/drivers/block/virtio_blk.c
> > > > > > +++ b/drivers/block/virtio_blk.c
> > > > > > @@ -24,6 +24,22 @@
> > > > > >    /* The maximum number of sg elements that fit into a virtqueue */
> > > > > >    #define VIRTIO_BLK_MAX_SG_ELEMS 32768
> > > > > > +static int virtblk_queue_count_set(const char *val,
> > > > > > +		const struct kernel_param *kp)
> > > > > > +{
> > > > > > +	return param_set_uint_minmax(val, kp, 1, nr_cpu_ids);
> > > > > > +}
> > 
> > Hmm which tree is this for?
> 
> I've mentioned in the note that it apply on branch for-5.15/drivers. But now
> you can apply it on linus/master as well.
> 
> 
> > 
> > > > > > +
> > > > > > +static const struct kernel_param_ops queue_count_ops = {
> > > > > > +	.set = virtblk_queue_count_set,
> > > > > > +	.get = param_get_uint,
> > > > > > +};
> > > > > > +
> > > > > > +static unsigned int num_io_queues;
> > > > > > +module_param_cb(num_io_queues, &queue_count_ops, &num_io_queues, 0644);
> > > > > > +MODULE_PARM_DESC(num_io_queues,
> > > > > > +		 "Number of IO virt queues to use for blk device. Should > 0");
> > 
> > 
> > better:
> > 
> > +MODULE_PARM_DESC(num_io_request_queues,
> > +                "Limit number of IO request virt queues to use for each device. 0 for now limit");
> 
> You proposed it and I replied on it bellow.


Can't say I understand 100% what you are saying. Want to send
a description that does make sense to you but
also reflects reality? 0 is the default so
"should > 0" besides being ungrammatical does not seem t"
reflect what it does ...

> 
> > 
> > 
> > > > > > +
> > > > > >    static int major;
> > > > > >    static DEFINE_IDA(vd_index_ida);
> > > > > > @@ -501,7 +517,9 @@ static int init_vq(struct virtio_blk *vblk)
> > > > > >    	if (err)
> > > > > >    		num_vqs = 1;
> > > > > > -	num_vqs = min_t(unsigned int, nr_cpu_ids, num_vqs);
> > > > > > +	num_vqs = min_t(unsigned int,
> > > > > > +			min_not_zero(num_io_queues, nr_cpu_ids),
> > > > > > +			num_vqs);
> > > > > If you respin, please consider calling them request queues. That's the
> > > > > terminology from the VIRTIO spec and it's nice to keep it consistent.
> > > > > But the purpose of num_io_queues is clear, so:
> > > > > 
> > > > > Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> > > > I did this:
> > > > +static unsigned int num_io_request_queues;
> > > > +module_param_cb(num_io_request_queues, &queue_count_ops, &num_io_request_queues, 0644);
> > > > +MODULE_PARM_DESC(num_io_request_queues,
> > > > +                "Limit number of IO request virt queues to use for each device. 0 for now limit");
> > > The parameter is writable and can be changed and then new devices might be
> > > probed with new value.
> > > 
> > > It can't be zero in the code. we can change param_set_uint_minmax args and
> > > say that 0 says nr_cpus.
> > > 
> > > I'm ok with the renaming but I prefer to stick to the description we gave in
> > > V3 of this patch (and maybe enable value of 0 as mentioned above).

Re: [PATCH v2 1/1] virtio-blk: add num_io_queues module parameter

[Max Gurtovoy]

On 9/9/2021 4:42 PM, Michael S. Tsirkin wrote:
> On Mon, Sep 06, 2021 at 02:59:40PM +0300, Max Gurtovoy wrote:
>> On 9/6/2021 2:20 PM, Michael S. Tsirkin wrote:
>>> On Mon, Sep 06, 2021 at 01:31:32AM +0300, Max Gurtovoy wrote:
>>>> On 9/5/2021 7:02 PM, Michael S. Tsirkin wrote:
>>>>> On Thu, Sep 02, 2021 at 02:45:52PM +0100, Stefan Hajnoczi wrote:
>>>>>> On Tue, Aug 31, 2021 at 04:50:35PM +0300, Max Gurtovoy wrote:
>>>>>>> Sometimes a user would like to control the amount of IO queues to be
>>>>>>> created for a block device. For example, for limiting the memory
>>>>>>> footprint of virtio-blk devices.
>>>>>>>
>>>>>>> Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
>>>>>>> ---
>>>>>>>
>>>>>>> changes from v1:
>>>>>>>     - use param_set_uint_minmax (from Christoph)
>>>>>>>     - added "Should > 0" to module description
>>>>>>>
>>>>>>> Note: This commit apply on top of Jens's branch for-5.15/drivers
>>>>>>> ---
>>>>>>>     drivers/block/virtio_blk.c | 20 +++++++++++++++++++-
>>>>>>>     1 file changed, 19 insertions(+), 1 deletion(-)
>>>>>>>
>>>>>>> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
>>>>>>> index 4b49df2dfd23..9332fc4e9b31 100644
>>>>>>> --- a/drivers/block/virtio_blk.c
>>>>>>> +++ b/drivers/block/virtio_blk.c
>>>>>>> @@ -24,6 +24,22 @@
>>>>>>>     /* The maximum number of sg elements that fit into a virtqueue */
>>>>>>>     #define VIRTIO_BLK_MAX_SG_ELEMS 32768
>>>>>>> +static int virtblk_queue_count_set(const char *val,
>>>>>>> +		const struct kernel_param *kp)
>>>>>>> +{
>>>>>>> +	return param_set_uint_minmax(val, kp, 1, nr_cpu_ids);
>>>>>>> +}
>>> Hmm which tree is this for?
>> I've mentioned in the note that it apply on branch for-5.15/drivers. But now
>> you can apply it on linus/master as well.
>>
>>
>>>>>>> +
>>>>>>> +static const struct kernel_param_ops queue_count_ops = {
>>>>>>> +	.set = virtblk_queue_count_set,
>>>>>>> +	.get = param_get_uint,
>>>>>>> +};
>>>>>>> +
>>>>>>> +static unsigned int num_io_queues;
>>>>>>> +module_param_cb(num_io_queues, &queue_count_ops, &num_io_queues, 0644);
>>>>>>> +MODULE_PARM_DESC(num_io_queues,
>>>>>>> +		 "Number of IO virt queues to use for blk device. Should > 0");
>>>
>>> better:
>>>
>>> +MODULE_PARM_DESC(num_io_request_queues,
>>> +                "Limit number of IO request virt queues to use for each device. 0 for now limit");
>> You proposed it and I replied on it bellow.
>
> Can't say I understand 100% what you are saying. Want to send
> a description that does make sense to you but
> also reflects reality? 0 is the default so
> "should > 0" besides being ungrammatical does not seem t"
> reflect what it does ...

if you "modprobe virtio_blk" the previous behavior will happen.

You can't "modprobe virtio_blk num_io_request_queues=0" since the 
minimal value is 1.

So your description is not reflecting the code.

We can do:

MODULE_PARM_DESC(num_io_request_queues, "Number of request virt queues to use for blk device. Minimum value is 1 queue");

>
>>>
>>>>>>> +
>>>>>>>     static int major;
>>>>>>>     static DEFINE_IDA(vd_index_ida);
>>>>>>> @@ -501,7 +517,9 @@ static int init_vq(struct virtio_blk *vblk)
>>>>>>>     	if (err)
>>>>>>>     		num_vqs = 1;
>>>>>>> -	num_vqs = min_t(unsigned int, nr_cpu_ids, num_vqs);
>>>>>>> +	num_vqs = min_t(unsigned int,
>>>>>>> +			min_not_zero(num_io_queues, nr_cpu_ids),
>>>>>>> +			num_vqs);
>>>>>> If you respin, please consider calling them request queues. That's the
>>>>>> terminology from the VIRTIO spec and it's nice to keep it consistent.
>>>>>> But the purpose of num_io_queues is clear, so:
>>>>>>
>>>>>> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
>>>>> I did this:
>>>>> +static unsigned int num_io_request_queues;
>>>>> +module_param_cb(num_io_request_queues, &queue_count_ops, &num_io_request_queues, 0644);
>>>>> +MODULE_PARM_DESC(num_io_request_queues,
>>>>> +                "Limit number of IO request virt queues to use for each device. 0 for now limit");
>>>> The parameter is writable and can be changed and then new devices might be
>>>> probed with new value.
>>>>
>>>> It can't be zero in the code. we can change param_set_uint_minmax args and
>>>> say that 0 says nr_cpus.
>>>>
>>>> I'm ok with the renaming but I prefer to stick to the description we gave in
>>>> V3 of this patch (and maybe enable value of 0 as mentioned above).

Re: [PATCH v2 1/1] virtio-blk: add num_io_queues module parameter

[Michael S. Tsirkin]

On Thu, Sep 09, 2021 at 06:37:37PM +0300, Max Gurtovoy wrote:
> 
> On 9/9/2021 4:42 PM, Michael S. Tsirkin wrote:
> > On Mon, Sep 06, 2021 at 02:59:40PM +0300, Max Gurtovoy wrote:
> > > On 9/6/2021 2:20 PM, Michael S. Tsirkin wrote:
> > > > On Mon, Sep 06, 2021 at 01:31:32AM +0300, Max Gurtovoy wrote:
> > > > > On 9/5/2021 7:02 PM, Michael S. Tsirkin wrote:
> > > > > > On Thu, Sep 02, 2021 at 02:45:52PM +0100, Stefan Hajnoczi wrote:
> > > > > > > On Tue, Aug 31, 2021 at 04:50:35PM +0300, Max Gurtovoy wrote:
> > > > > > > > Sometimes a user would like to control the amount of IO queues to be
> > > > > > > > created for a block device. For example, for limiting the memory
> > > > > > > > footprint of virtio-blk devices.
> > > > > > > > 
> > > > > > > > Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
> > > > > > > > ---
> > > > > > > > 
> > > > > > > > changes from v1:
> > > > > > > >     - use param_set_uint_minmax (from Christoph)
> > > > > > > >     - added "Should > 0" to module description
> > > > > > > > 
> > > > > > > > Note: This commit apply on top of Jens's branch for-5.15/drivers
> > > > > > > > ---
> > > > > > > >     drivers/block/virtio_blk.c | 20 +++++++++++++++++++-
> > > > > > > >     1 file changed, 19 insertions(+), 1 deletion(-)
> > > > > > > > 
> > > > > > > > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> > > > > > > > index 4b49df2dfd23..9332fc4e9b31 100644
> > > > > > > > --- a/drivers/block/virtio_blk.c
> > > > > > > > +++ b/drivers/block/virtio_blk.c
> > > > > > > > @@ -24,6 +24,22 @@
> > > > > > > >     /* The maximum number of sg elements that fit into a virtqueue */
> > > > > > > >     #define VIRTIO_BLK_MAX_SG_ELEMS 32768
> > > > > > > > +static int virtblk_queue_count_set(const char *val,
> > > > > > > > +		const struct kernel_param *kp)
> > > > > > > > +{
> > > > > > > > +	return param_set_uint_minmax(val, kp, 1, nr_cpu_ids);
> > > > > > > > +}
> > > > Hmm which tree is this for?
> > > I've mentioned in the note that it apply on branch for-5.15/drivers. But now
> > > you can apply it on linus/master as well.
> > > 
> > > 
> > > > > > > > +
> > > > > > > > +static const struct kernel_param_ops queue_count_ops = {
> > > > > > > > +	.set = virtblk_queue_count_set,
> > > > > > > > +	.get = param_get_uint,
> > > > > > > > +};
> > > > > > > > +
> > > > > > > > +static unsigned int num_io_queues;
> > > > > > > > +module_param_cb(num_io_queues, &queue_count_ops, &num_io_queues, 0644);
> > > > > > > > +MODULE_PARM_DESC(num_io_queues,
> > > > > > > > +		 "Number of IO virt queues to use for blk device. Should > 0");
> > > > 
> > > > better:
> > > > 
> > > > +MODULE_PARM_DESC(num_io_request_queues,
> > > > +                "Limit number of IO request virt queues to use for each device. 0 for now limit");
> > > You proposed it and I replied on it bellow.
> > 
> > Can't say I understand 100% what you are saying. Want to send
> > a description that does make sense to you but
> > also reflects reality? 0 is the default so
> > "should > 0" besides being ungrammatical does not seem t"
> > reflect what it does ...
> 
> if you "modprobe virtio_blk" the previous behavior will happen.
> 
> You can't "modprobe virtio_blk num_io_request_queues=0" since the minimal
> value is 1.
> 
> So your description is not reflecting the code.
> 
> We can do:
> 
> MODULE_PARM_DESC(num_io_request_queues, "Number of request virt queues to use for blk device. Minimum value is 1 queue");

What's the default value? We should document that.

> > 
> > > > 
> > > > > > > > +
> > > > > > > >     static int major;
> > > > > > > >     static DEFINE_IDA(vd_index_ida);
> > > > > > > > @@ -501,7 +517,9 @@ static int init_vq(struct virtio_blk *vblk)
> > > > > > > >     	if (err)
> > > > > > > >     		num_vqs = 1;
> > > > > > > > -	num_vqs = min_t(unsigned int, nr_cpu_ids, num_vqs);
> > > > > > > > +	num_vqs = min_t(unsigned int,
> > > > > > > > +			min_not_zero(num_io_queues, nr_cpu_ids),
> > > > > > > > +			num_vqs);
> > > > > > > If you respin, please consider calling them request queues. That's the
> > > > > > > terminology from the VIRTIO spec and it's nice to keep it consistent.
> > > > > > > But the purpose of num_io_queues is clear, so:
> > > > > > > 
> > > > > > > Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> > > > > > I did this:
> > > > > > +static unsigned int num_io_request_queues;
> > > > > > +module_param_cb(num_io_request_queues, &queue_count_ops, &num_io_request_queues, 0644);
> > > > > > +MODULE_PARM_DESC(num_io_request_queues,
> > > > > > +                "Limit number of IO request virt queues to use for each device. 0 for now limit");
> > > > > The parameter is writable and can be changed and then new devices might be
> > > > > probed with new value.
> > > > > 
> > > > > It can't be zero in the code. we can change param_set_uint_minmax args and
> > > > > say that 0 says nr_cpus.
> > > > > 
> > > > > I'm ok with the renaming but I prefer to stick to the description we gave in
> > > > > V3 of this patch (and maybe enable value of 0 as mentioned above).

Re: [PATCH v2 1/1] virtio-blk: add num_io_queues module parameter

[Michael S. Tsirkin]

On Thu, Sep 09, 2021 at 06:37:37PM +0300, Max Gurtovoy wrote:
> 
> On 9/9/2021 4:42 PM, Michael S. Tsirkin wrote:
> > On Mon, Sep 06, 2021 at 02:59:40PM +0300, Max Gurtovoy wrote:
> > > On 9/6/2021 2:20 PM, Michael S. Tsirkin wrote:
> > > > On Mon, Sep 06, 2021 at 01:31:32AM +0300, Max Gurtovoy wrote:
> > > > > On 9/5/2021 7:02 PM, Michael S. Tsirkin wrote:
> > > > > > On Thu, Sep 02, 2021 at 02:45:52PM +0100, Stefan Hajnoczi wrote:
> > > > > > > On Tue, Aug 31, 2021 at 04:50:35PM +0300, Max Gurtovoy wrote:
> > > > > > > > Sometimes a user would like to control the amount of IO queues to be
> > > > > > > > created for a block device. For example, for limiting the memory
> > > > > > > > footprint of virtio-blk devices.
> > > > > > > > 
> > > > > > > > Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
> > > > > > > > ---
> > > > > > > > 
> > > > > > > > changes from v1:
> > > > > > > >     - use param_set_uint_minmax (from Christoph)
> > > > > > > >     - added "Should > 0" to module description
> > > > > > > > 
> > > > > > > > Note: This commit apply on top of Jens's branch for-5.15/drivers
> > > > > > > > ---
> > > > > > > >     drivers/block/virtio_blk.c | 20 +++++++++++++++++++-
> > > > > > > >     1 file changed, 19 insertions(+), 1 deletion(-)
> > > > > > > > 
> > > > > > > > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> > > > > > > > index 4b49df2dfd23..9332fc4e9b31 100644
> > > > > > > > --- a/drivers/block/virtio_blk.c
> > > > > > > > +++ b/drivers/block/virtio_blk.c
> > > > > > > > @@ -24,6 +24,22 @@
> > > > > > > >     /* The maximum number of sg elements that fit into a virtqueue */
> > > > > > > >     #define VIRTIO_BLK_MAX_SG_ELEMS 32768
> > > > > > > > +static int virtblk_queue_count_set(const char *val,
> > > > > > > > +		const struct kernel_param *kp)
> > > > > > > > +{
> > > > > > > > +	return param_set_uint_minmax(val, kp, 1, nr_cpu_ids);
> > > > > > > > +}
> > > > Hmm which tree is this for?
> > > I've mentioned in the note that it apply on branch for-5.15/drivers. But now
> > > you can apply it on linus/master as well.
> > > 
> > > 
> > > > > > > > +
> > > > > > > > +static const struct kernel_param_ops queue_count_ops = {
> > > > > > > > +	.set = virtblk_queue_count_set,
> > > > > > > > +	.get = param_get_uint,
> > > > > > > > +};
> > > > > > > > +
> > > > > > > > +static unsigned int num_io_queues;
> > > > > > > > +module_param_cb(num_io_queues, &queue_count_ops, &num_io_queues, 0644);
> > > > > > > > +MODULE_PARM_DESC(num_io_queues,
> > > > > > > > +		 "Number of IO virt queues to use for blk device. Should > 0");
> > > > 
> > > > better:
> > > > 
> > > > +MODULE_PARM_DESC(num_io_request_queues,
> > > > +                "Limit number of IO request virt queues to use for each device. 0 for now limit");
> > > You proposed it and I replied on it bellow.
> > 
> > Can't say I understand 100% what you are saying. Want to send
> > a description that does make sense to you but
> > also reflects reality? 0 is the default so
> > "should > 0" besides being ungrammatical does not seem t"
> > reflect what it does ...
> 
> if you "modprobe virtio_blk" the previous behavior will happen.
> 
> You can't "modprobe virtio_blk num_io_request_queues=0" since the minimal
> value is 1.
> 
> So your description is not reflecting the code.
> 
> We can do:
> 
> MODULE_PARM_DESC(num_io_request_queues, "Number of request virt queues to use for blk device. Minimum value is 1 queue");

What's the default value? We should document that.

> > 
> > > > 
> > > > > > > > +
> > > > > > > >     static int major;
> > > > > > > >     static DEFINE_IDA(vd_index_ida);
> > > > > > > > @@ -501,7 +517,9 @@ static int init_vq(struct virtio_blk *vblk)
> > > > > > > >     	if (err)
> > > > > > > >     		num_vqs = 1;
> > > > > > > > -	num_vqs = min_t(unsigned int, nr_cpu_ids, num_vqs);
> > > > > > > > +	num_vqs = min_t(unsigned int,
> > > > > > > > +			min_not_zero(num_io_queues, nr_cpu_ids),
> > > > > > > > +			num_vqs);
> > > > > > > If you respin, please consider calling them request queues. That's the
> > > > > > > terminology from the VIRTIO spec and it's nice to keep it consistent.
> > > > > > > But the purpose of num_io_queues is clear, so:
> > > > > > > 
> > > > > > > Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> > > > > > I did this:
> > > > > > +static unsigned int num_io_request_queues;
> > > > > > +module_param_cb(num_io_request_queues, &queue_count_ops, &num_io_request_queues, 0644);
> > > > > > +MODULE_PARM_DESC(num_io_request_queues,
> > > > > > +                "Limit number of IO request virt queues to use for each device. 0 for now limit");
> > > > > The parameter is writable and can be changed and then new devices might be
> > > > > probed with new value.
> > > > > 
> > > > > It can't be zero in the code. we can change param_set_uint_minmax args and
> > > > > say that 0 says nr_cpus.
> > > > > 
> > > > > I'm ok with the renaming but I prefer to stick to the description we gave in
> > > > > V3 of this patch (and maybe enable value of 0 as mentioned above).

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Re: [PATCH v2 1/1] virtio-blk: add num_io_queues module parameter

[Max Gurtovoy]

On 9/9/2021 6:40 PM, Michael S. Tsirkin wrote:
> On Thu, Sep 09, 2021 at 06:37:37PM +0300, Max Gurtovoy wrote:
>> On 9/9/2021 4:42 PM, Michael S. Tsirkin wrote:
>>> On Mon, Sep 06, 2021 at 02:59:40PM +0300, Max Gurtovoy wrote:
>>>> On 9/6/2021 2:20 PM, Michael S. Tsirkin wrote:
>>>>> On Mon, Sep 06, 2021 at 01:31:32AM +0300, Max Gurtovoy wrote:
>>>>>> On 9/5/2021 7:02 PM, Michael S. Tsirkin wrote:
>>>>>>> On Thu, Sep 02, 2021 at 02:45:52PM +0100, Stefan Hajnoczi wrote:
>>>>>>>> On Tue, Aug 31, 2021 at 04:50:35PM +0300, Max Gurtovoy wrote:
>>>>>>>>> Sometimes a user would like to control the amount of IO queues to be
>>>>>>>>> created for a block device. For example, for limiting the memory
>>>>>>>>> footprint of virtio-blk devices.
>>>>>>>>>
>>>>>>>>> Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
>>>>>>>>> ---
>>>>>>>>>
>>>>>>>>> changes from v1:
>>>>>>>>>      - use param_set_uint_minmax (from Christoph)
>>>>>>>>>      - added "Should > 0" to module description
>>>>>>>>>
>>>>>>>>> Note: This commit apply on top of Jens's branch for-5.15/drivers
>>>>>>>>> ---
>>>>>>>>>      drivers/block/virtio_blk.c | 20 +++++++++++++++++++-
>>>>>>>>>      1 file changed, 19 insertions(+), 1 deletion(-)
>>>>>>>>>
>>>>>>>>> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
>>>>>>>>> index 4b49df2dfd23..9332fc4e9b31 100644
>>>>>>>>> --- a/drivers/block/virtio_blk.c
>>>>>>>>> +++ b/drivers/block/virtio_blk.c
>>>>>>>>> @@ -24,6 +24,22 @@
>>>>>>>>>      /* The maximum number of sg elements that fit into a virtqueue */
>>>>>>>>>      #define VIRTIO_BLK_MAX_SG_ELEMS 32768
>>>>>>>>> +static int virtblk_queue_count_set(const char *val,
>>>>>>>>> +		const struct kernel_param *kp)
>>>>>>>>> +{
>>>>>>>>> +	return param_set_uint_minmax(val, kp, 1, nr_cpu_ids);
>>>>>>>>> +}
>>>>> Hmm which tree is this for?
>>>> I've mentioned in the note that it apply on branch for-5.15/drivers. But now
>>>> you can apply it on linus/master as well.
>>>>
>>>>
>>>>>>>>> +
>>>>>>>>> +static const struct kernel_param_ops queue_count_ops = {
>>>>>>>>> +	.set = virtblk_queue_count_set,
>>>>>>>>> +	.get = param_get_uint,
>>>>>>>>> +};
>>>>>>>>> +
>>>>>>>>> +static unsigned int num_io_queues;
>>>>>>>>> +module_param_cb(num_io_queues, &queue_count_ops, &num_io_queues, 0644);
>>>>>>>>> +MODULE_PARM_DESC(num_io_queues,
>>>>>>>>> +		 "Number of IO virt queues to use for blk device. Should > 0");
>>>>> better:
>>>>>
>>>>> +MODULE_PARM_DESC(num_io_request_queues,
>>>>> +                "Limit number of IO request virt queues to use for each device. 0 for now limit");
>>>> You proposed it and I replied on it bellow.
>>> Can't say I understand 100% what you are saying. Want to send
>>> a description that does make sense to you but
>>> also reflects reality? 0 is the default so
>>> "should > 0" besides being ungrammatical does not seem t"
>>> reflect what it does ...
>> if you "modprobe virtio_blk" the previous behavior will happen.
>>
>> You can't "modprobe virtio_blk num_io_request_queues=0" since the minimal
>> value is 1.
>>
>> So your description is not reflecting the code.
>>
>> We can do:
>>
>> MODULE_PARM_DESC(num_io_request_queues, "Number of request virt queues to use for blk device. Minimum value is 1 queue");
> What's the default value? We should document that.

default value for static global variables is 0.

MODULE_PARM_DESC(num_io_request_queues, "Number of request virt queues 
to use for blk device. Minimum value is 1 queue. Default and Maximum 
value is equal to the total number of CPUs");


>
>>>>>>>>> +
>>>>>>>>>      static int major;
>>>>>>>>>      static DEFINE_IDA(vd_index_ida);
>>>>>>>>> @@ -501,7 +517,9 @@ static int init_vq(struct virtio_blk *vblk)
>>>>>>>>>      	if (err)
>>>>>>>>>      		num_vqs = 1;
>>>>>>>>> -	num_vqs = min_t(unsigned int, nr_cpu_ids, num_vqs);
>>>>>>>>> +	num_vqs = min_t(unsigned int,
>>>>>>>>> +			min_not_zero(num_io_queues, nr_cpu_ids),
>>>>>>>>> +			num_vqs);
>>>>>>>> If you respin, please consider calling them request queues. That's the
>>>>>>>> terminology from the VIRTIO spec and it's nice to keep it consistent.
>>>>>>>> But the purpose of num_io_queues is clear, so:
>>>>>>>>
>>>>>>>> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
>>>>>>> I did this:
>>>>>>> +static unsigned int num_io_request_queues;
>>>>>>> +module_param_cb(num_io_request_queues, &queue_count_ops, &num_io_request_queues, 0644);
>>>>>>> +MODULE_PARM_DESC(num_io_request_queues,
>>>>>>> +                "Limit number of IO request virt queues to use for each device. 0 for now limit");
>>>>>> The parameter is writable and can be changed and then new devices might be
>>>>>> probed with new value.
>>>>>>
>>>>>> It can't be zero in the code. we can change param_set_uint_minmax args and
>>>>>> say that 0 says nr_cpus.
>>>>>>
>>>>>> I'm ok with the renaming but I prefer to stick to the description we gave in
>>>>>> V3 of this patch (and maybe enable value of 0 as mentioned above).

Re: [PATCH v2 1/1] virtio-blk: add num_io_queues module parameter

[Michael S. Tsirkin]

On Thu, Sep 09, 2021 at 06:51:56PM +0300, Max Gurtovoy wrote:
> 
> On 9/9/2021 6:40 PM, Michael S. Tsirkin wrote:
> > On Thu, Sep 09, 2021 at 06:37:37PM +0300, Max Gurtovoy wrote:
> > > On 9/9/2021 4:42 PM, Michael S. Tsirkin wrote:
> > > > On Mon, Sep 06, 2021 at 02:59:40PM +0300, Max Gurtovoy wrote:
> > > > > On 9/6/2021 2:20 PM, Michael S. Tsirkin wrote:
> > > > > > On Mon, Sep 06, 2021 at 01:31:32AM +0300, Max Gurtovoy wrote:
> > > > > > > On 9/5/2021 7:02 PM, Michael S. Tsirkin wrote:
> > > > > > > > On Thu, Sep 02, 2021 at 02:45:52PM +0100, Stefan Hajnoczi wrote:
> > > > > > > > > On Tue, Aug 31, 2021 at 04:50:35PM +0300, Max Gurtovoy wrote:
> > > > > > > > > > Sometimes a user would like to control the amount of IO queues to be
> > > > > > > > > > created for a block device. For example, for limiting the memory
> > > > > > > > > > footprint of virtio-blk devices.
> > > > > > > > > > 
> > > > > > > > > > Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
> > > > > > > > > > ---
> > > > > > > > > > 
> > > > > > > > > > changes from v1:
> > > > > > > > > >      - use param_set_uint_minmax (from Christoph)
> > > > > > > > > >      - added "Should > 0" to module description
> > > > > > > > > > 
> > > > > > > > > > Note: This commit apply on top of Jens's branch for-5.15/drivers
> > > > > > > > > > ---
> > > > > > > > > >      drivers/block/virtio_blk.c | 20 +++++++++++++++++++-
> > > > > > > > > >      1 file changed, 19 insertions(+), 1 deletion(-)
> > > > > > > > > > 
> > > > > > > > > > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> > > > > > > > > > index 4b49df2dfd23..9332fc4e9b31 100644
> > > > > > > > > > --- a/drivers/block/virtio_blk.c
> > > > > > > > > > +++ b/drivers/block/virtio_blk.c
> > > > > > > > > > @@ -24,6 +24,22 @@
> > > > > > > > > >      /* The maximum number of sg elements that fit into a virtqueue */
> > > > > > > > > >      #define VIRTIO_BLK_MAX_SG_ELEMS 32768
> > > > > > > > > > +static int virtblk_queue_count_set(const char *val,
> > > > > > > > > > +		const struct kernel_param *kp)
> > > > > > > > > > +{
> > > > > > > > > > +	return param_set_uint_minmax(val, kp, 1, nr_cpu_ids);
> > > > > > > > > > +}
> > > > > > Hmm which tree is this for?
> > > > > I've mentioned in the note that it apply on branch for-5.15/drivers. But now
> > > > > you can apply it on linus/master as well.
> > > > > 
> > > > > 
> > > > > > > > > > +
> > > > > > > > > > +static const struct kernel_param_ops queue_count_ops = {
> > > > > > > > > > +	.set = virtblk_queue_count_set,
> > > > > > > > > > +	.get = param_get_uint,
> > > > > > > > > > +};
> > > > > > > > > > +
> > > > > > > > > > +static unsigned int num_io_queues;
> > > > > > > > > > +module_param_cb(num_io_queues, &queue_count_ops, &num_io_queues, 0644);
> > > > > > > > > > +MODULE_PARM_DESC(num_io_queues,
> > > > > > > > > > +		 "Number of IO virt queues to use for blk device. Should > 0");
> > > > > > better:
> > > > > > 
> > > > > > +MODULE_PARM_DESC(num_io_request_queues,
> > > > > > +                "Limit number of IO request virt queues to use for each device. 0 for now limit");
> > > > > You proposed it and I replied on it bellow.
> > > > Can't say I understand 100% what you are saying. Want to send
> > > > a description that does make sense to you but
> > > > also reflects reality? 0 is the default so
> > > > "should > 0" besides being ungrammatical does not seem t"
> > > > reflect what it does ...
> > > if you "modprobe virtio_blk" the previous behavior will happen.
> > > 
> > > You can't "modprobe virtio_blk num_io_request_queues=0" since the minimal
> > > value is 1.
> > > 
> > > So your description is not reflecting the code.
> > > 
> > > We can do:
> > > 
> > > MODULE_PARM_DESC(num_io_request_queues, "Number of request virt queues to use for blk device. Minimum value is 1 queue");
> > What's the default value? We should document that.
> 
> default value for static global variables is 0.
> 
> MODULE_PARM_DESC(num_io_request_queues, "Number of request virt queues to
> use for blk device. Minimum value is 1 queue. Default and Maximum value is
> equal to the total number of CPUs");

So it says it's the # of cpus but yoiu inspect it with
sysfs and it's actually 0. Let's say that's confusing
at the least. why not just let users set it to 0
and document that?


> 
> > 
> > > > > > > > > > +
> > > > > > > > > >      static int major;
> > > > > > > > > >      static DEFINE_IDA(vd_index_ida);
> > > > > > > > > > @@ -501,7 +517,9 @@ static int init_vq(struct virtio_blk *vblk)
> > > > > > > > > >      	if (err)
> > > > > > > > > >      		num_vqs = 1;
> > > > > > > > > > -	num_vqs = min_t(unsigned int, nr_cpu_ids, num_vqs);
> > > > > > > > > > +	num_vqs = min_t(unsigned int,
> > > > > > > > > > +			min_not_zero(num_io_queues, nr_cpu_ids),
> > > > > > > > > > +			num_vqs);
> > > > > > > > > If you respin, please consider calling them request queues. That's the
> > > > > > > > > terminology from the VIRTIO spec and it's nice to keep it consistent.
> > > > > > > > > But the purpose of num_io_queues is clear, so:
> > > > > > > > > 
> > > > > > > > > Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> > > > > > > > I did this:
> > > > > > > > +static unsigned int num_io_request_queues;
> > > > > > > > +module_param_cb(num_io_request_queues, &queue_count_ops, &num_io_request_queues, 0644);
> > > > > > > > +MODULE_PARM_DESC(num_io_request_queues,
> > > > > > > > +                "Limit number of IO request virt queues to use for each device. 0 for now limit");
> > > > > > > The parameter is writable and can be changed and then new devices might be
> > > > > > > probed with new value.
> > > > > > > 
> > > > > > > It can't be zero in the code. we can change param_set_uint_minmax args and
> > > > > > > say that 0 says nr_cpus.
> > > > > > > 
> > > > > > > I'm ok with the renaming but I prefer to stick to the description we gave in
> > > > > > > V3 of this patch (and maybe enable value of 0 as mentioned above).

Re: [PATCH v2 1/1] virtio-blk: add num_io_queues module parameter

[Michael S. Tsirkin]

On Thu, Sep 09, 2021 at 06:51:56PM +0300, Max Gurtovoy wrote:
> 
> On 9/9/2021 6:40 PM, Michael S. Tsirkin wrote:
> > On Thu, Sep 09, 2021 at 06:37:37PM +0300, Max Gurtovoy wrote:
> > > On 9/9/2021 4:42 PM, Michael S. Tsirkin wrote:
> > > > On Mon, Sep 06, 2021 at 02:59:40PM +0300, Max Gurtovoy wrote:
> > > > > On 9/6/2021 2:20 PM, Michael S. Tsirkin wrote:
> > > > > > On Mon, Sep 06, 2021 at 01:31:32AM +0300, Max Gurtovoy wrote:
> > > > > > > On 9/5/2021 7:02 PM, Michael S. Tsirkin wrote:
> > > > > > > > On Thu, Sep 02, 2021 at 02:45:52PM +0100, Stefan Hajnoczi wrote:
> > > > > > > > > On Tue, Aug 31, 2021 at 04:50:35PM +0300, Max Gurtovoy wrote:
> > > > > > > > > > Sometimes a user would like to control the amount of IO queues to be
> > > > > > > > > > created for a block device. For example, for limiting the memory
> > > > > > > > > > footprint of virtio-blk devices.
> > > > > > > > > > 
> > > > > > > > > > Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
> > > > > > > > > > ---
> > > > > > > > > > 
> > > > > > > > > > changes from v1:
> > > > > > > > > >      - use param_set_uint_minmax (from Christoph)
> > > > > > > > > >      - added "Should > 0" to module description
> > > > > > > > > > 
> > > > > > > > > > Note: This commit apply on top of Jens's branch for-5.15/drivers
> > > > > > > > > > ---
> > > > > > > > > >      drivers/block/virtio_blk.c | 20 +++++++++++++++++++-
> > > > > > > > > >      1 file changed, 19 insertions(+), 1 deletion(-)
> > > > > > > > > > 
> > > > > > > > > > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> > > > > > > > > > index 4b49df2dfd23..9332fc4e9b31 100644
> > > > > > > > > > --- a/drivers/block/virtio_blk.c
> > > > > > > > > > +++ b/drivers/block/virtio_blk.c
> > > > > > > > > > @@ -24,6 +24,22 @@
> > > > > > > > > >      /* The maximum number of sg elements that fit into a virtqueue */
> > > > > > > > > >      #define VIRTIO_BLK_MAX_SG_ELEMS 32768
> > > > > > > > > > +static int virtblk_queue_count_set(const char *val,
> > > > > > > > > > +		const struct kernel_param *kp)
> > > > > > > > > > +{
> > > > > > > > > > +	return param_set_uint_minmax(val, kp, 1, nr_cpu_ids);
> > > > > > > > > > +}
> > > > > > Hmm which tree is this for?
> > > > > I've mentioned in the note that it apply on branch for-5.15/drivers. But now
> > > > > you can apply it on linus/master as well.
> > > > > 
> > > > > 
> > > > > > > > > > +
> > > > > > > > > > +static const struct kernel_param_ops queue_count_ops = {
> > > > > > > > > > +	.set = virtblk_queue_count_set,
> > > > > > > > > > +	.get = param_get_uint,
> > > > > > > > > > +};
> > > > > > > > > > +
> > > > > > > > > > +static unsigned int num_io_queues;
> > > > > > > > > > +module_param_cb(num_io_queues, &queue_count_ops, &num_io_queues, 0644);
> > > > > > > > > > +MODULE_PARM_DESC(num_io_queues,
> > > > > > > > > > +		 "Number of IO virt queues to use for blk device. Should > 0");
> > > > > > better:
> > > > > > 
> > > > > > +MODULE_PARM_DESC(num_io_request_queues,
> > > > > > +                "Limit number of IO request virt queues to use for each device. 0 for now limit");
> > > > > You proposed it and I replied on it bellow.
> > > > Can't say I understand 100% what you are saying. Want to send
> > > > a description that does make sense to you but
> > > > also reflects reality? 0 is the default so
> > > > "should > 0" besides being ungrammatical does not seem t"
> > > > reflect what it does ...
> > > if you "modprobe virtio_blk" the previous behavior will happen.
> > > 
> > > You can't "modprobe virtio_blk num_io_request_queues=0" since the minimal
> > > value is 1.
> > > 
> > > So your description is not reflecting the code.
> > > 
> > > We can do:
> > > 
> > > MODULE_PARM_DESC(num_io_request_queues, "Number of request virt queues to use for blk device. Minimum value is 1 queue");
> > What's the default value? We should document that.
> 
> default value for static global variables is 0.
> 
> MODULE_PARM_DESC(num_io_request_queues, "Number of request virt queues to
> use for blk device. Minimum value is 1 queue. Default and Maximum value is
> equal to the total number of CPUs");

So it says it's the # of cpus but yoiu inspect it with
sysfs and it's actually 0. Let's say that's confusing
at the least. why not just let users set it to 0
and document that?


> 
> > 
> > > > > > > > > > +
> > > > > > > > > >      static int major;
> > > > > > > > > >      static DEFINE_IDA(vd_index_ida);
> > > > > > > > > > @@ -501,7 +517,9 @@ static int init_vq(struct virtio_blk *vblk)
> > > > > > > > > >      	if (err)
> > > > > > > > > >      		num_vqs = 1;
> > > > > > > > > > -	num_vqs = min_t(unsigned int, nr_cpu_ids, num_vqs);
> > > > > > > > > > +	num_vqs = min_t(unsigned int,
> > > > > > > > > > +			min_not_zero(num_io_queues, nr_cpu_ids),
> > > > > > > > > > +			num_vqs);
> > > > > > > > > If you respin, please consider calling them request queues. That's the
> > > > > > > > > terminology from the VIRTIO spec and it's nice to keep it consistent.
> > > > > > > > > But the purpose of num_io_queues is clear, so:
> > > > > > > > > 
> > > > > > > > > Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> > > > > > > > I did this:
> > > > > > > > +static unsigned int num_io_request_queues;
> > > > > > > > +module_param_cb(num_io_request_queues, &queue_count_ops, &num_io_request_queues, 0644);
> > > > > > > > +MODULE_PARM_DESC(num_io_request_queues,
> > > > > > > > +                "Limit number of IO request virt queues to use for each device. 0 for now limit");
> > > > > > > The parameter is writable and can be changed and then new devices might be
> > > > > > > probed with new value.
> > > > > > > 
> > > > > > > It can't be zero in the code. we can change param_set_uint_minmax args and
> > > > > > > say that 0 says nr_cpus.
> > > > > > > 
> > > > > > > I'm ok with the renaming but I prefer to stick to the description we gave in
> > > > > > > V3 of this patch (and maybe enable value of 0 as mentioned above).

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Re: [PATCH v2 1/1] virtio-blk: add num_io_queues module parameter

[Max Gurtovoy]

On 9/9/2021 7:31 PM, Michael S. Tsirkin wrote:
> On Thu, Sep 09, 2021 at 06:51:56PM +0300, Max Gurtovoy wrote:
>> On 9/9/2021 6:40 PM, Michael S. Tsirkin wrote:
>>> On Thu, Sep 09, 2021 at 06:37:37PM +0300, Max Gurtovoy wrote:
>>>> On 9/9/2021 4:42 PM, Michael S. Tsirkin wrote:
>>>>> On Mon, Sep 06, 2021 at 02:59:40PM +0300, Max Gurtovoy wrote:
>>>>>> On 9/6/2021 2:20 PM, Michael S. Tsirkin wrote:
>>>>>>> On Mon, Sep 06, 2021 at 01:31:32AM +0300, Max Gurtovoy wrote:
>>>>>>>> On 9/5/2021 7:02 PM, Michael S. Tsirkin wrote:
>>>>>>>>> On Thu, Sep 02, 2021 at 02:45:52PM +0100, Stefan Hajnoczi wrote:
>>>>>>>>>> On Tue, Aug 31, 2021 at 04:50:35PM +0300, Max Gurtovoy wrote:
>>>>>>>>>>> Sometimes a user would like to control the amount of IO queues to be
>>>>>>>>>>> created for a block device. For example, for limiting the memory
>>>>>>>>>>> footprint of virtio-blk devices.
>>>>>>>>>>>
>>>>>>>>>>> Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
>>>>>>>>>>> ---
>>>>>>>>>>>
>>>>>>>>>>> changes from v1:
>>>>>>>>>>>       - use param_set_uint_minmax (from Christoph)
>>>>>>>>>>>       - added "Should > 0" to module description
>>>>>>>>>>>
>>>>>>>>>>> Note: This commit apply on top of Jens's branch for-5.15/drivers
>>>>>>>>>>> ---
>>>>>>>>>>>       drivers/block/virtio_blk.c | 20 +++++++++++++++++++-
>>>>>>>>>>>       1 file changed, 19 insertions(+), 1 deletion(-)
>>>>>>>>>>>
>>>>>>>>>>> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
>>>>>>>>>>> index 4b49df2dfd23..9332fc4e9b31 100644
>>>>>>>>>>> --- a/drivers/block/virtio_blk.c
>>>>>>>>>>> +++ b/drivers/block/virtio_blk.c
>>>>>>>>>>> @@ -24,6 +24,22 @@
>>>>>>>>>>>       /* The maximum number of sg elements that fit into a virtqueue */
>>>>>>>>>>>       #define VIRTIO_BLK_MAX_SG_ELEMS 32768
>>>>>>>>>>> +static int virtblk_queue_count_set(const char *val,
>>>>>>>>>>> +		const struct kernel_param *kp)
>>>>>>>>>>> +{
>>>>>>>>>>> +	return param_set_uint_minmax(val, kp, 1, nr_cpu_ids);
>>>>>>>>>>> +}
>>>>>>> Hmm which tree is this for?
>>>>>> I've mentioned in the note that it apply on branch for-5.15/drivers. But now
>>>>>> you can apply it on linus/master as well.
>>>>>>
>>>>>>
>>>>>>>>>>> +
>>>>>>>>>>> +static const struct kernel_param_ops queue_count_ops = {
>>>>>>>>>>> +	.set = virtblk_queue_count_set,
>>>>>>>>>>> +	.get = param_get_uint,
>>>>>>>>>>> +};
>>>>>>>>>>> +
>>>>>>>>>>> +static unsigned int num_io_queues;
>>>>>>>>>>> +module_param_cb(num_io_queues, &queue_count_ops, &num_io_queues, 0644);
>>>>>>>>>>> +MODULE_PARM_DESC(num_io_queues,
>>>>>>>>>>> +		 "Number of IO virt queues to use for blk device. Should > 0");
>>>>>>> better:
>>>>>>>
>>>>>>> +MODULE_PARM_DESC(num_io_request_queues,
>>>>>>> +                "Limit number of IO request virt queues to use for each device. 0 for now limit");
>>>>>> You proposed it and I replied on it bellow.
>>>>> Can't say I understand 100% what you are saying. Want to send
>>>>> a description that does make sense to you but
>>>>> also reflects reality? 0 is the default so
>>>>> "should > 0" besides being ungrammatical does not seem t"
>>>>> reflect what it does ...
>>>> if you "modprobe virtio_blk" the previous behavior will happen.
>>>>
>>>> You can't "modprobe virtio_blk num_io_request_queues=0" since the minimal
>>>> value is 1.
>>>>
>>>> So your description is not reflecting the code.
>>>>
>>>> We can do:
>>>>
>>>> MODULE_PARM_DESC(num_io_request_queues, "Number of request virt queues to use for blk device. Minimum value is 1 queue");
>>> What's the default value? We should document that.
>> default value for static global variables is 0.
>>
>> MODULE_PARM_DESC(num_io_request_queues, "Number of request virt queues to
>> use for blk device. Minimum value is 1 queue. Default and Maximum value is
>> equal to the total number of CPUs");
> So it says it's the # of cpus but yoiu inspect it with
> sysfs and it's actually 0. Let's say that's confusing
> at the least. why not just let users set it to 0
> and document that?
>
Setting it by the user to 0 makes no sense.

We can say "if not set, the value equals to the total number of CPUs".

The actual value of the created queues can be seen in /sys/block/vda/mq/ 
as done today.

>>>>>>>>>>> +
>>>>>>>>>>>       static int major;
>>>>>>>>>>>       static DEFINE_IDA(vd_index_ida);
>>>>>>>>>>> @@ -501,7 +517,9 @@ static int init_vq(struct virtio_blk *vblk)
>>>>>>>>>>>       	if (err)
>>>>>>>>>>>       		num_vqs = 1;
>>>>>>>>>>> -	num_vqs = min_t(unsigned int, nr_cpu_ids, num_vqs);
>>>>>>>>>>> +	num_vqs = min_t(unsigned int,
>>>>>>>>>>> +			min_not_zero(num_io_queues, nr_cpu_ids),
>>>>>>>>>>> +			num_vqs);
>>>>>>>>>> If you respin, please consider calling them request queues. That's the
>>>>>>>>>> terminology from the VIRTIO spec and it's nice to keep it consistent.
>>>>>>>>>> But the purpose of num_io_queues is clear, so:
>>>>>>>>>>
>>>>>>>>>> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
>>>>>>>>> I did this:
>>>>>>>>> +static unsigned int num_io_request_queues;
>>>>>>>>> +module_param_cb(num_io_request_queues, &queue_count_ops, &num_io_request_queues, 0644);
>>>>>>>>> +MODULE_PARM_DESC(num_io_request_queues,
>>>>>>>>> +                "Limit number of IO request virt queues to use for each device. 0 for now limit");
>>>>>>>> The parameter is writable and can be changed and then new devices might be
>>>>>>>> probed with new value.
>>>>>>>>
>>>>>>>> It can't be zero in the code. we can change param_set_uint_minmax args and
>>>>>>>> say that 0 says nr_cpus.
>>>>>>>>
>>>>>>>> I'm ok with the renaming but I prefer to stick to the description we gave in
>>>>>>>> V3 of this patch (and maybe enable value of 0 as mentioned above).

Re: [PATCH v2 1/1] virtio-blk: add num_io_queues module parameter

[Michael S. Tsirkin]

On Thu, Sep 09, 2021 at 07:45:42PM +0300, Max Gurtovoy wrote:
> 
> On 9/9/2021 7:31 PM, Michael S. Tsirkin wrote:
> > On Thu, Sep 09, 2021 at 06:51:56PM +0300, Max Gurtovoy wrote:
> > > On 9/9/2021 6:40 PM, Michael S. Tsirkin wrote:
> > > > On Thu, Sep 09, 2021 at 06:37:37PM +0300, Max Gurtovoy wrote:
> > > > > On 9/9/2021 4:42 PM, Michael S. Tsirkin wrote:
> > > > > > On Mon, Sep 06, 2021 at 02:59:40PM +0300, Max Gurtovoy wrote:
> > > > > > > On 9/6/2021 2:20 PM, Michael S. Tsirkin wrote:
> > > > > > > > On Mon, Sep 06, 2021 at 01:31:32AM +0300, Max Gurtovoy wrote:
> > > > > > > > > On 9/5/2021 7:02 PM, Michael S. Tsirkin wrote:
> > > > > > > > > > On Thu, Sep 02, 2021 at 02:45:52PM +0100, Stefan Hajnoczi wrote:
> > > > > > > > > > > On Tue, Aug 31, 2021 at 04:50:35PM +0300, Max Gurtovoy wrote:
> > > > > > > > > > > > Sometimes a user would like to control the amount of IO queues to be
> > > > > > > > > > > > created for a block device. For example, for limiting the memory
> > > > > > > > > > > > footprint of virtio-blk devices.
> > > > > > > > > > > > 
> > > > > > > > > > > > Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
> > > > > > > > > > > > ---
> > > > > > > > > > > > 
> > > > > > > > > > > > changes from v1:
> > > > > > > > > > > >       - use param_set_uint_minmax (from Christoph)
> > > > > > > > > > > >       - added "Should > 0" to module description
> > > > > > > > > > > > 
> > > > > > > > > > > > Note: This commit apply on top of Jens's branch for-5.15/drivers
> > > > > > > > > > > > ---
> > > > > > > > > > > >       drivers/block/virtio_blk.c | 20 +++++++++++++++++++-
> > > > > > > > > > > >       1 file changed, 19 insertions(+), 1 deletion(-)
> > > > > > > > > > > > 
> > > > > > > > > > > > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> > > > > > > > > > > > index 4b49df2dfd23..9332fc4e9b31 100644
> > > > > > > > > > > > --- a/drivers/block/virtio_blk.c
> > > > > > > > > > > > +++ b/drivers/block/virtio_blk.c
> > > > > > > > > > > > @@ -24,6 +24,22 @@
> > > > > > > > > > > >       /* The maximum number of sg elements that fit into a virtqueue */
> > > > > > > > > > > >       #define VIRTIO_BLK_MAX_SG_ELEMS 32768
> > > > > > > > > > > > +static int virtblk_queue_count_set(const char *val,
> > > > > > > > > > > > +		const struct kernel_param *kp)
> > > > > > > > > > > > +{
> > > > > > > > > > > > +	return param_set_uint_minmax(val, kp, 1, nr_cpu_ids);
> > > > > > > > > > > > +}
> > > > > > > > Hmm which tree is this for?
> > > > > > > I've mentioned in the note that it apply on branch for-5.15/drivers. But now
> > > > > > > you can apply it on linus/master as well.
> > > > > > > 
> > > > > > > 
> > > > > > > > > > > > +
> > > > > > > > > > > > +static const struct kernel_param_ops queue_count_ops = {
> > > > > > > > > > > > +	.set = virtblk_queue_count_set,
> > > > > > > > > > > > +	.get = param_get_uint,
> > > > > > > > > > > > +};
> > > > > > > > > > > > +
> > > > > > > > > > > > +static unsigned int num_io_queues;
> > > > > > > > > > > > +module_param_cb(num_io_queues, &queue_count_ops, &num_io_queues, 0644);
> > > > > > > > > > > > +MODULE_PARM_DESC(num_io_queues,
> > > > > > > > > > > > +		 "Number of IO virt queues to use for blk device. Should > 0");
> > > > > > > > better:
> > > > > > > > 
> > > > > > > > +MODULE_PARM_DESC(num_io_request_queues,
> > > > > > > > +                "Limit number of IO request virt queues to use for each device. 0 for now limit");
> > > > > > > You proposed it and I replied on it bellow.
> > > > > > Can't say I understand 100% what you are saying. Want to send
> > > > > > a description that does make sense to you but
> > > > > > also reflects reality? 0 is the default so
> > > > > > "should > 0" besides being ungrammatical does not seem t"
> > > > > > reflect what it does ...
> > > > > if you "modprobe virtio_blk" the previous behavior will happen.
> > > > > 
> > > > > You can't "modprobe virtio_blk num_io_request_queues=0" since the minimal
> > > > > value is 1.
> > > > > 
> > > > > So your description is not reflecting the code.
> > > > > 
> > > > > We can do:
> > > > > 
> > > > > MODULE_PARM_DESC(num_io_request_queues, "Number of request virt queues to use for blk device. Minimum value is 1 queue");
> > > > What's the default value? We should document that.
> > > default value for static global variables is 0.
> > > 
> > > MODULE_PARM_DESC(num_io_request_queues, "Number of request virt queues to
> > > use for blk device. Minimum value is 1 queue. Default and Maximum value is
> > > equal to the total number of CPUs");
> > So it says it's the # of cpus but yoiu inspect it with
> > sysfs and it's actually 0. Let's say that's confusing
> > at the least. why not just let users set it to 0
> > and document that?
> > 
> Setting it by the user to 0 makes no sense.
> 
> We can say "if not set, the value equals to the total number of CPUs".

the value is 0. it seems to mean "no limit". the actual # of queues is
then te smaller between # of cpus and # of hardware queues.
I see no reason not to allow user to set that especially if
it was originally the value then user changed it
and is trying to change it back.

> The actual value of the created queues can be seen in /sys/block/vda/mq/ as
> done today.

> > > > > > > > > > > > +
> > > > > > > > > > > >       static int major;
> > > > > > > > > > > >       static DEFINE_IDA(vd_index_ida);
> > > > > > > > > > > > @@ -501,7 +517,9 @@ static int init_vq(struct virtio_blk *vblk)
> > > > > > > > > > > >       	if (err)
> > > > > > > > > > > >       		num_vqs = 1;
> > > > > > > > > > > > -	num_vqs = min_t(unsigned int, nr_cpu_ids, num_vqs);
> > > > > > > > > > > > +	num_vqs = min_t(unsigned int,
> > > > > > > > > > > > +			min_not_zero(num_io_queues, nr_cpu_ids),
> > > > > > > > > > > > +			num_vqs);
> > > > > > > > > > > If you respin, please consider calling them request queues. That's the
> > > > > > > > > > > terminology from the VIRTIO spec and it's nice to keep it consistent.
> > > > > > > > > > > But the purpose of num_io_queues is clear, so:
> > > > > > > > > > > 
> > > > > > > > > > > Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> > > > > > > > > > I did this:
> > > > > > > > > > +static unsigned int num_io_request_queues;
> > > > > > > > > > +module_param_cb(num_io_request_queues, &queue_count_ops, &num_io_request_queues, 0644);
> > > > > > > > > > +MODULE_PARM_DESC(num_io_request_queues,
> > > > > > > > > > +                "Limit number of IO request virt queues to use for each device. 0 for now limit");
> > > > > > > > > The parameter is writable and can be changed and then new devices might be
> > > > > > > > > probed with new value.
> > > > > > > > > 
> > > > > > > > > It can't be zero in the code. we can change param_set_uint_minmax args and
> > > > > > > > > say that 0 says nr_cpus.
> > > > > > > > > 
> > > > > > > > > I'm ok with the renaming but I prefer to stick to the description we gave in
> > > > > > > > > V3 of this patch (and maybe enable value of 0 as mentioned above).

Re: [PATCH v2 1/1] virtio-blk: add num_io_queues module parameter

[Michael S. Tsirkin]

On Thu, Sep 09, 2021 at 07:45:42PM +0300, Max Gurtovoy wrote:
> 
> On 9/9/2021 7:31 PM, Michael S. Tsirkin wrote:
> > On Thu, Sep 09, 2021 at 06:51:56PM +0300, Max Gurtovoy wrote:
> > > On 9/9/2021 6:40 PM, Michael S. Tsirkin wrote:
> > > > On Thu, Sep 09, 2021 at 06:37:37PM +0300, Max Gurtovoy wrote:
> > > > > On 9/9/2021 4:42 PM, Michael S. Tsirkin wrote:
> > > > > > On Mon, Sep 06, 2021 at 02:59:40PM +0300, Max Gurtovoy wrote:
> > > > > > > On 9/6/2021 2:20 PM, Michael S. Tsirkin wrote:
> > > > > > > > On Mon, Sep 06, 2021 at 01:31:32AM +0300, Max Gurtovoy wrote:
> > > > > > > > > On 9/5/2021 7:02 PM, Michael S. Tsirkin wrote:
> > > > > > > > > > On Thu, Sep 02, 2021 at 02:45:52PM +0100, Stefan Hajnoczi wrote:
> > > > > > > > > > > On Tue, Aug 31, 2021 at 04:50:35PM +0300, Max Gurtovoy wrote:
> > > > > > > > > > > > Sometimes a user would like to control the amount of IO queues to be
> > > > > > > > > > > > created for a block device. For example, for limiting the memory
> > > > > > > > > > > > footprint of virtio-blk devices.
> > > > > > > > > > > > 
> > > > > > > > > > > > Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
> > > > > > > > > > > > ---
> > > > > > > > > > > > 
> > > > > > > > > > > > changes from v1:
> > > > > > > > > > > >       - use param_set_uint_minmax (from Christoph)
> > > > > > > > > > > >       - added "Should > 0" to module description
> > > > > > > > > > > > 
> > > > > > > > > > > > Note: This commit apply on top of Jens's branch for-5.15/drivers
> > > > > > > > > > > > ---
> > > > > > > > > > > >       drivers/block/virtio_blk.c | 20 +++++++++++++++++++-
> > > > > > > > > > > >       1 file changed, 19 insertions(+), 1 deletion(-)
> > > > > > > > > > > > 
> > > > > > > > > > > > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> > > > > > > > > > > > index 4b49df2dfd23..9332fc4e9b31 100644
> > > > > > > > > > > > --- a/drivers/block/virtio_blk.c
> > > > > > > > > > > > +++ b/drivers/block/virtio_blk.c
> > > > > > > > > > > > @@ -24,6 +24,22 @@
> > > > > > > > > > > >       /* The maximum number of sg elements that fit into a virtqueue */
> > > > > > > > > > > >       #define VIRTIO_BLK_MAX_SG_ELEMS 32768
> > > > > > > > > > > > +static int virtblk_queue_count_set(const char *val,
> > > > > > > > > > > > +		const struct kernel_param *kp)
> > > > > > > > > > > > +{
> > > > > > > > > > > > +	return param_set_uint_minmax(val, kp, 1, nr_cpu_ids);
> > > > > > > > > > > > +}
> > > > > > > > Hmm which tree is this for?
> > > > > > > I've mentioned in the note that it apply on branch for-5.15/drivers. But now
> > > > > > > you can apply it on linus/master as well.
> > > > > > > 
> > > > > > > 
> > > > > > > > > > > > +
> > > > > > > > > > > > +static const struct kernel_param_ops queue_count_ops = {
> > > > > > > > > > > > +	.set = virtblk_queue_count_set,
> > > > > > > > > > > > +	.get = param_get_uint,
> > > > > > > > > > > > +};
> > > > > > > > > > > > +
> > > > > > > > > > > > +static unsigned int num_io_queues;
> > > > > > > > > > > > +module_param_cb(num_io_queues, &queue_count_ops, &num_io_queues, 0644);
> > > > > > > > > > > > +MODULE_PARM_DESC(num_io_queues,
> > > > > > > > > > > > +		 "Number of IO virt queues to use for blk device. Should > 0");
> > > > > > > > better:
> > > > > > > > 
> > > > > > > > +MODULE_PARM_DESC(num_io_request_queues,
> > > > > > > > +                "Limit number of IO request virt queues to use for each device. 0 for now limit");
> > > > > > > You proposed it and I replied on it bellow.
> > > > > > Can't say I understand 100% what you are saying. Want to send
> > > > > > a description that does make sense to you but
> > > > > > also reflects reality? 0 is the default so
> > > > > > "should > 0" besides being ungrammatical does not seem t"
> > > > > > reflect what it does ...
> > > > > if you "modprobe virtio_blk" the previous behavior will happen.
> > > > > 
> > > > > You can't "modprobe virtio_blk num_io_request_queues=0" since the minimal
> > > > > value is 1.
> > > > > 
> > > > > So your description is not reflecting the code.
> > > > > 
> > > > > We can do:
> > > > > 
> > > > > MODULE_PARM_DESC(num_io_request_queues, "Number of request virt queues to use for blk device. Minimum value is 1 queue");
> > > > What's the default value? We should document that.
> > > default value for static global variables is 0.
> > > 
> > > MODULE_PARM_DESC(num_io_request_queues, "Number of request virt queues to
> > > use for blk device. Minimum value is 1 queue. Default and Maximum value is
> > > equal to the total number of CPUs");
> > So it says it's the # of cpus but yoiu inspect it with
> > sysfs and it's actually 0. Let's say that's confusing
> > at the least. why not just let users set it to 0
> > and document that?
> > 
> Setting it by the user to 0 makes no sense.
> 
> We can say "if not set, the value equals to the total number of CPUs".

the value is 0. it seems to mean "no limit". the actual # of queues is
then te smaller between # of cpus and # of hardware queues.
I see no reason not to allow user to set that especially if
it was originally the value then user changed it
and is trying to change it back.

> The actual value of the created queues can be seen in /sys/block/vda/mq/ as
> done today.

> > > > > > > > > > > > +
> > > > > > > > > > > >       static int major;
> > > > > > > > > > > >       static DEFINE_IDA(vd_index_ida);
> > > > > > > > > > > > @@ -501,7 +517,9 @@ static int init_vq(struct virtio_blk *vblk)
> > > > > > > > > > > >       	if (err)
> > > > > > > > > > > >       		num_vqs = 1;
> > > > > > > > > > > > -	num_vqs = min_t(unsigned int, nr_cpu_ids, num_vqs);
> > > > > > > > > > > > +	num_vqs = min_t(unsigned int,
> > > > > > > > > > > > +			min_not_zero(num_io_queues, nr_cpu_ids),
> > > > > > > > > > > > +			num_vqs);
> > > > > > > > > > > If you respin, please consider calling them request queues. That's the
> > > > > > > > > > > terminology from the VIRTIO spec and it's nice to keep it consistent.
> > > > > > > > > > > But the purpose of num_io_queues is clear, so:
> > > > > > > > > > > 
> > > > > > > > > > > Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> > > > > > > > > > I did this:
> > > > > > > > > > +static unsigned int num_io_request_queues;
> > > > > > > > > > +module_param_cb(num_io_request_queues, &queue_count_ops, &num_io_request_queues, 0644);
> > > > > > > > > > +MODULE_PARM_DESC(num_io_request_queues,
> > > > > > > > > > +                "Limit number of IO request virt queues to use for each device. 0 for now limit");
> > > > > > > > > The parameter is writable and can be changed and then new devices might be
> > > > > > > > > probed with new value.
> > > > > > > > > 
> > > > > > > > > It can't be zero in the code. we can change param_set_uint_minmax args and
> > > > > > > > > say that 0 says nr_cpus.
> > > > > > > > > 
> > > > > > > > > I'm ok with the renaming but I prefer to stick to the description we gave in
> > > > > > > > > V3 of this patch (and maybe enable value of 0 as mentioned above).

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Re: [PATCH v2 1/1] virtio-blk: add num_io_queues module parameter

[Max Gurtovoy]

On 9/10/2021 1:57 AM, Michael S. Tsirkin wrote:
> On Thu, Sep 09, 2021 at 07:45:42PM +0300, Max Gurtovoy wrote:
>> On 9/9/2021 7:31 PM, Michael S. Tsirkin wrote:
>>> On Thu, Sep 09, 2021 at 06:51:56PM +0300, Max Gurtovoy wrote:
>>>> On 9/9/2021 6:40 PM, Michael S. Tsirkin wrote:
>>>>> On Thu, Sep 09, 2021 at 06:37:37PM +0300, Max Gurtovoy wrote:
>>>>>> On 9/9/2021 4:42 PM, Michael S. Tsirkin wrote:
>>>>>>> On Mon, Sep 06, 2021 at 02:59:40PM +0300, Max Gurtovoy wrote:
>>>>>>>> On 9/6/2021 2:20 PM, Michael S. Tsirkin wrote:
>>>>>>>>> On Mon, Sep 06, 2021 at 01:31:32AM +0300, Max Gurtovoy wrote:
>>>>>>>>>> On 9/5/2021 7:02 PM, Michael S. Tsirkin wrote:
>>>>>>>>>>> On Thu, Sep 02, 2021 at 02:45:52PM +0100, Stefan Hajnoczi wrote:
>>>>>>>>>>>> On Tue, Aug 31, 2021 at 04:50:35PM +0300, Max Gurtovoy wrote:
>>>>>>>>>>>>> Sometimes a user would like to control the amount of IO queues to be
>>>>>>>>>>>>> created for a block device. For example, for limiting the memory
>>>>>>>>>>>>> footprint of virtio-blk devices.
>>>>>>>>>>>>>
>>>>>>>>>>>>> Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
>>>>>>>>>>>>> ---
>>>>>>>>>>>>>
>>>>>>>>>>>>> changes from v1:
>>>>>>>>>>>>>        - use param_set_uint_minmax (from Christoph)
>>>>>>>>>>>>>        - added "Should > 0" to module description
>>>>>>>>>>>>>
>>>>>>>>>>>>> Note: This commit apply on top of Jens's branch for-5.15/drivers
>>>>>>>>>>>>> ---
>>>>>>>>>>>>>        drivers/block/virtio_blk.c | 20 +++++++++++++++++++-
>>>>>>>>>>>>>        1 file changed, 19 insertions(+), 1 deletion(-)
>>>>>>>>>>>>>
>>>>>>>>>>>>> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
>>>>>>>>>>>>> index 4b49df2dfd23..9332fc4e9b31 100644
>>>>>>>>>>>>> --- a/drivers/block/virtio_blk.c
>>>>>>>>>>>>> +++ b/drivers/block/virtio_blk.c
>>>>>>>>>>>>> @@ -24,6 +24,22 @@
>>>>>>>>>>>>>        /* The maximum number of sg elements that fit into a virtqueue */
>>>>>>>>>>>>>        #define VIRTIO_BLK_MAX_SG_ELEMS 32768
>>>>>>>>>>>>> +static int virtblk_queue_count_set(const char *val,
>>>>>>>>>>>>> +		const struct kernel_param *kp)
>>>>>>>>>>>>> +{
>>>>>>>>>>>>> +	return param_set_uint_minmax(val, kp, 1, nr_cpu_ids);
>>>>>>>>>>>>> +}
>>>>>>>>> Hmm which tree is this for?
>>>>>>>> I've mentioned in the note that it apply on branch for-5.15/drivers. But now
>>>>>>>> you can apply it on linus/master as well.
>>>>>>>>
>>>>>>>>
>>>>>>>>>>>>> +
>>>>>>>>>>>>> +static const struct kernel_param_ops queue_count_ops = {
>>>>>>>>>>>>> +	.set = virtblk_queue_count_set,
>>>>>>>>>>>>> +	.get = param_get_uint,
>>>>>>>>>>>>> +};
>>>>>>>>>>>>> +
>>>>>>>>>>>>> +static unsigned int num_io_queues;
>>>>>>>>>>>>> +module_param_cb(num_io_queues, &queue_count_ops, &num_io_queues, 0644);
>>>>>>>>>>>>> +MODULE_PARM_DESC(num_io_queues,
>>>>>>>>>>>>> +		 "Number of IO virt queues to use for blk device. Should > 0");
>>>>>>>>> better:
>>>>>>>>>
>>>>>>>>> +MODULE_PARM_DESC(num_io_request_queues,
>>>>>>>>> +                "Limit number of IO request virt queues to use for each device. 0 for now limit");
>>>>>>>> You proposed it and I replied on it bellow.
>>>>>>> Can't say I understand 100% what you are saying. Want to send
>>>>>>> a description that does make sense to you but
>>>>>>> also reflects reality? 0 is the default so
>>>>>>> "should > 0" besides being ungrammatical does not seem t"
>>>>>>> reflect what it does ...
>>>>>> if you "modprobe virtio_blk" the previous behavior will happen.
>>>>>>
>>>>>> You can't "modprobe virtio_blk num_io_request_queues=0" since the minimal
>>>>>> value is 1.
>>>>>>
>>>>>> So your description is not reflecting the code.
>>>>>>
>>>>>> We can do:
>>>>>>
>>>>>> MODULE_PARM_DESC(num_io_request_queues, "Number of request virt queues to use for blk device. Minimum value is 1 queue");
>>>>> What's the default value? We should document that.
>>>> default value for static global variables is 0.
>>>>
>>>> MODULE_PARM_DESC(num_io_request_queues, "Number of request virt queues to
>>>> use for blk device. Minimum value is 1 queue. Default and Maximum value is
>>>> equal to the total number of CPUs");
>>> So it says it's the # of cpus but yoiu inspect it with
>>> sysfs and it's actually 0. Let's say that's confusing
>>> at the least. why not just let users set it to 0
>>> and document that?
>>>
>> Setting it by the user to 0 makes no sense.
>>
>> We can say "if not set, the value equals to the total number of CPUs".
> the value is 0. it seems to mean "no limit". the actual # of queues is
> then te smaller between # of cpus and # of hardware queues.
> I see no reason not to allow user to set that especially if
> it was originally the value then user changed it
> and is trying to change it back.

I fine with that.

MODULE_PARM_DESC(num_io_request_queues, "Number of request virt queues to use for blk device. 0 value means no limitation");


>
>> The actual value of the created queues can be seen in /sys/block/vda/mq/ as
>> done today.
>>>>>>>>>>>>> +
>>>>>>>>>>>>>        static int major;
>>>>>>>>>>>>>        static DEFINE_IDA(vd_index_ida);
>>>>>>>>>>>>> @@ -501,7 +517,9 @@ static int init_vq(struct virtio_blk *vblk)
>>>>>>>>>>>>>        	if (err)
>>>>>>>>>>>>>        		num_vqs = 1;
>>>>>>>>>>>>> -	num_vqs = min_t(unsigned int, nr_cpu_ids, num_vqs);
>>>>>>>>>>>>> +	num_vqs = min_t(unsigned int,
>>>>>>>>>>>>> +			min_not_zero(num_io_queues, nr_cpu_ids),
>>>>>>>>>>>>> +			num_vqs);
>>>>>>>>>>>> If you respin, please consider calling them request queues. That's the
>>>>>>>>>>>> terminology from the VIRTIO spec and it's nice to keep it consistent.
>>>>>>>>>>>> But the purpose of num_io_queues is clear, so:
>>>>>>>>>>>>
>>>>>>>>>>>> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
>>>>>>>>>>> I did this:
>>>>>>>>>>> +static unsigned int num_io_request_queues;
>>>>>>>>>>> +module_param_cb(num_io_request_queues, &queue_count_ops, &num_io_request_queues, 0644);
>>>>>>>>>>> +MODULE_PARM_DESC(num_io_request_queues,
>>>>>>>>>>> +                "Limit number of IO request virt queues to use for each device. 0 for now limit");
>>>>>>>>>> The parameter is writable and can be changed and then new devices might be
>>>>>>>>>> probed with new value.
>>>>>>>>>>
>>>>>>>>>> It can't be zero in the code. we can change param_set_uint_minmax args and
>>>>>>>>>> say that 0 says nr_cpus.
>>>>>>>>>>
>>>>>>>>>> I'm ok with the renaming but I prefer to stick to the description we gave in
>>>>>>>>>> V3 of this patch (and maybe enable value of 0 as mentioned above).

Re: [PATCH v2 1/1] virtio-blk: add num_io_queues module parameter

[Michael S. Tsirkin]

On Sat, Sep 11, 2021 at 03:56:45PM +0300, Max Gurtovoy wrote:
> 
> On 9/10/2021 1:57 AM, Michael S. Tsirkin wrote:
> > On Thu, Sep 09, 2021 at 07:45:42PM +0300, Max Gurtovoy wrote:
> > > On 9/9/2021 7:31 PM, Michael S. Tsirkin wrote:
> > > > On Thu, Sep 09, 2021 at 06:51:56PM +0300, Max Gurtovoy wrote:
> > > > > On 9/9/2021 6:40 PM, Michael S. Tsirkin wrote:
> > > > > > On Thu, Sep 09, 2021 at 06:37:37PM +0300, Max Gurtovoy wrote:
> > > > > > > On 9/9/2021 4:42 PM, Michael S. Tsirkin wrote:
> > > > > > > > On Mon, Sep 06, 2021 at 02:59:40PM +0300, Max Gurtovoy wrote:
> > > > > > > > > On 9/6/2021 2:20 PM, Michael S. Tsirkin wrote:
> > > > > > > > > > On Mon, Sep 06, 2021 at 01:31:32AM +0300, Max Gurtovoy wrote:
> > > > > > > > > > > On 9/5/2021 7:02 PM, Michael S. Tsirkin wrote:
> > > > > > > > > > > > On Thu, Sep 02, 2021 at 02:45:52PM +0100, Stefan Hajnoczi wrote:
> > > > > > > > > > > > > On Tue, Aug 31, 2021 at 04:50:35PM +0300, Max Gurtovoy wrote:
> > > > > > > > > > > > > > Sometimes a user would like to control the amount of IO queues to be
> > > > > > > > > > > > > > created for a block device. For example, for limiting the memory
> > > > > > > > > > > > > > footprint of virtio-blk devices.
> > > > > > > > > > > > > > 
> > > > > > > > > > > > > > Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
> > > > > > > > > > > > > > ---
> > > > > > > > > > > > > > 
> > > > > > > > > > > > > > changes from v1:
> > > > > > > > > > > > > >        - use param_set_uint_minmax (from Christoph)
> > > > > > > > > > > > > >        - added "Should > 0" to module description
> > > > > > > > > > > > > > 
> > > > > > > > > > > > > > Note: This commit apply on top of Jens's branch for-5.15/drivers
> > > > > > > > > > > > > > ---
> > > > > > > > > > > > > >        drivers/block/virtio_blk.c | 20 +++++++++++++++++++-
> > > > > > > > > > > > > >        1 file changed, 19 insertions(+), 1 deletion(-)
> > > > > > > > > > > > > > 
> > > > > > > > > > > > > > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> > > > > > > > > > > > > > index 4b49df2dfd23..9332fc4e9b31 100644
> > > > > > > > > > > > > > --- a/drivers/block/virtio_blk.c
> > > > > > > > > > > > > > +++ b/drivers/block/virtio_blk.c
> > > > > > > > > > > > > > @@ -24,6 +24,22 @@
> > > > > > > > > > > > > >        /* The maximum number of sg elements that fit into a virtqueue */
> > > > > > > > > > > > > >        #define VIRTIO_BLK_MAX_SG_ELEMS 32768
> > > > > > > > > > > > > > +static int virtblk_queue_count_set(const char *val,
> > > > > > > > > > > > > > +		const struct kernel_param *kp)
> > > > > > > > > > > > > > +{
> > > > > > > > > > > > > > +	return param_set_uint_minmax(val, kp, 1, nr_cpu_ids);
> > > > > > > > > > > > > > +}
> > > > > > > > > > Hmm which tree is this for?
> > > > > > > > > I've mentioned in the note that it apply on branch for-5.15/drivers. But now
> > > > > > > > > you can apply it on linus/master as well.
> > > > > > > > > 
> > > > > > > > > 
> > > > > > > > > > > > > > +
> > > > > > > > > > > > > > +static const struct kernel_param_ops queue_count_ops = {
> > > > > > > > > > > > > > +	.set = virtblk_queue_count_set,
> > > > > > > > > > > > > > +	.get = param_get_uint,
> > > > > > > > > > > > > > +};
> > > > > > > > > > > > > > +
> > > > > > > > > > > > > > +static unsigned int num_io_queues;
> > > > > > > > > > > > > > +module_param_cb(num_io_queues, &queue_count_ops, &num_io_queues, 0644);
> > > > > > > > > > > > > > +MODULE_PARM_DESC(num_io_queues,
> > > > > > > > > > > > > > +		 "Number of IO virt queues to use for blk device. Should > 0");
> > > > > > > > > > better:
> > > > > > > > > > 
> > > > > > > > > > +MODULE_PARM_DESC(num_io_request_queues,
> > > > > > > > > > +                "Limit number of IO request virt queues to use for each device. 0 for now limit");
> > > > > > > > > You proposed it and I replied on it bellow.
> > > > > > > > Can't say I understand 100% what you are saying. Want to send
> > > > > > > > a description that does make sense to you but
> > > > > > > > also reflects reality? 0 is the default so
> > > > > > > > "should > 0" besides being ungrammatical does not seem t"
> > > > > > > > reflect what it does ...
> > > > > > > if you "modprobe virtio_blk" the previous behavior will happen.
> > > > > > > 
> > > > > > > You can't "modprobe virtio_blk num_io_request_queues=0" since the minimal
> > > > > > > value is 1.
> > > > > > > 
> > > > > > > So your description is not reflecting the code.
> > > > > > > 
> > > > > > > We can do:
> > > > > > > 
> > > > > > > MODULE_PARM_DESC(num_io_request_queues, "Number of request virt queues to use for blk device. Minimum value is 1 queue");
> > > > > > What's the default value? We should document that.
> > > > > default value for static global variables is 0.
> > > > > 
> > > > > MODULE_PARM_DESC(num_io_request_queues, "Number of request virt queues to
> > > > > use for blk device. Minimum value is 1 queue. Default and Maximum value is
> > > > > equal to the total number of CPUs");
> > > > So it says it's the # of cpus but yoiu inspect it with
> > > > sysfs and it's actually 0. Let's say that's confusing
> > > > at the least. why not just let users set it to 0
> > > > and document that?
> > > > 
> > > Setting it by the user to 0 makes no sense.
> > > 
> > > We can say "if not set, the value equals to the total number of CPUs".
> > the value is 0. it seems to mean "no limit". the actual # of queues is
> > then te smaller between # of cpus and # of hardware queues.
> > I see no reason not to allow user to set that especially if
> > it was originally the value then user changed it
> > and is trying to change it back.
> 
> I fine with that.
> 
> MODULE_PARM_DESC(num_io_request_queues, "Number of request virt queues to use for blk device. 0 value means no limitation");
> 

OK and the second distinction is that it's a limit on the
number, not the actual number. It's never more than what's provided
by the hypervisor.

> > 
> > > The actual value of the created queues can be seen in /sys/block/vda/mq/ as
> > > done today.
> > > > > > > > > > > > > > +
> > > > > > > > > > > > > >        static int major;
> > > > > > > > > > > > > >        static DEFINE_IDA(vd_index_ida);
> > > > > > > > > > > > > > @@ -501,7 +517,9 @@ static int init_vq(struct virtio_blk *vblk)
> > > > > > > > > > > > > >        	if (err)
> > > > > > > > > > > > > >        		num_vqs = 1;
> > > > > > > > > > > > > > -	num_vqs = min_t(unsigned int, nr_cpu_ids, num_vqs);
> > > > > > > > > > > > > > +	num_vqs = min_t(unsigned int,
> > > > > > > > > > > > > > +			min_not_zero(num_io_queues, nr_cpu_ids),
> > > > > > > > > > > > > > +			num_vqs);
> > > > > > > > > > > > > If you respin, please consider calling them request queues. That's the
> > > > > > > > > > > > > terminology from the VIRTIO spec and it's nice to keep it consistent.
> > > > > > > > > > > > > But the purpose of num_io_queues is clear, so:
> > > > > > > > > > > > > 
> > > > > > > > > > > > > Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> > > > > > > > > > > > I did this:
> > > > > > > > > > > > +static unsigned int num_io_request_queues;
> > > > > > > > > > > > +module_param_cb(num_io_request_queues, &queue_count_ops, &num_io_request_queues, 0644);
> > > > > > > > > > > > +MODULE_PARM_DESC(num_io_request_queues,
> > > > > > > > > > > > +                "Limit number of IO request virt queues to use for each device. 0 for now limit");
> > > > > > > > > > > The parameter is writable and can be changed and then new devices might be
> > > > > > > > > > > probed with new value.
> > > > > > > > > > > 
> > > > > > > > > > > It can't be zero in the code. we can change param_set_uint_minmax args and
> > > > > > > > > > > say that 0 says nr_cpus.
> > > > > > > > > > > 
> > > > > > > > > > > I'm ok with the renaming but I prefer to stick to the description we gave in
> > > > > > > > > > > V3 of this patch (and maybe enable value of 0 as mentioned above).

Re: [PATCH v2 1/1] virtio-blk: add num_io_queues module parameter

[Michael S. Tsirkin]

On Sat, Sep 11, 2021 at 03:56:45PM +0300, Max Gurtovoy wrote:
> 
> On 9/10/2021 1:57 AM, Michael S. Tsirkin wrote:
> > On Thu, Sep 09, 2021 at 07:45:42PM +0300, Max Gurtovoy wrote:
> > > On 9/9/2021 7:31 PM, Michael S. Tsirkin wrote:
> > > > On Thu, Sep 09, 2021 at 06:51:56PM +0300, Max Gurtovoy wrote:
> > > > > On 9/9/2021 6:40 PM, Michael S. Tsirkin wrote:
> > > > > > On Thu, Sep 09, 2021 at 06:37:37PM +0300, Max Gurtovoy wrote:
> > > > > > > On 9/9/2021 4:42 PM, Michael S. Tsirkin wrote:
> > > > > > > > On Mon, Sep 06, 2021 at 02:59:40PM +0300, Max Gurtovoy wrote:
> > > > > > > > > On 9/6/2021 2:20 PM, Michael S. Tsirkin wrote:
> > > > > > > > > > On Mon, Sep 06, 2021 at 01:31:32AM +0300, Max Gurtovoy wrote:
> > > > > > > > > > > On 9/5/2021 7:02 PM, Michael S. Tsirkin wrote:
> > > > > > > > > > > > On Thu, Sep 02, 2021 at 02:45:52PM +0100, Stefan Hajnoczi wrote:
> > > > > > > > > > > > > On Tue, Aug 31, 2021 at 04:50:35PM +0300, Max Gurtovoy wrote:
> > > > > > > > > > > > > > Sometimes a user would like to control the amount of IO queues to be
> > > > > > > > > > > > > > created for a block device. For example, for limiting the memory
> > > > > > > > > > > > > > footprint of virtio-blk devices.
> > > > > > > > > > > > > > 
> > > > > > > > > > > > > > Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
> > > > > > > > > > > > > > ---
> > > > > > > > > > > > > > 
> > > > > > > > > > > > > > changes from v1:
> > > > > > > > > > > > > >        - use param_set_uint_minmax (from Christoph)
> > > > > > > > > > > > > >        - added "Should > 0" to module description
> > > > > > > > > > > > > > 
> > > > > > > > > > > > > > Note: This commit apply on top of Jens's branch for-5.15/drivers
> > > > > > > > > > > > > > ---
> > > > > > > > > > > > > >        drivers/block/virtio_blk.c | 20 +++++++++++++++++++-
> > > > > > > > > > > > > >        1 file changed, 19 insertions(+), 1 deletion(-)
> > > > > > > > > > > > > > 
> > > > > > > > > > > > > > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> > > > > > > > > > > > > > index 4b49df2dfd23..9332fc4e9b31 100644
> > > > > > > > > > > > > > --- a/drivers/block/virtio_blk.c
> > > > > > > > > > > > > > +++ b/drivers/block/virtio_blk.c
> > > > > > > > > > > > > > @@ -24,6 +24,22 @@
> > > > > > > > > > > > > >        /* The maximum number of sg elements that fit into a virtqueue */
> > > > > > > > > > > > > >        #define VIRTIO_BLK_MAX_SG_ELEMS 32768
> > > > > > > > > > > > > > +static int virtblk_queue_count_set(const char *val,
> > > > > > > > > > > > > > +		const struct kernel_param *kp)
> > > > > > > > > > > > > > +{
> > > > > > > > > > > > > > +	return param_set_uint_minmax(val, kp, 1, nr_cpu_ids);
> > > > > > > > > > > > > > +}
> > > > > > > > > > Hmm which tree is this for?
> > > > > > > > > I've mentioned in the note that it apply on branch for-5.15/drivers. But now
> > > > > > > > > you can apply it on linus/master as well.
> > > > > > > > > 
> > > > > > > > > 
> > > > > > > > > > > > > > +
> > > > > > > > > > > > > > +static const struct kernel_param_ops queue_count_ops = {
> > > > > > > > > > > > > > +	.set = virtblk_queue_count_set,
> > > > > > > > > > > > > > +	.get = param_get_uint,
> > > > > > > > > > > > > > +};
> > > > > > > > > > > > > > +
> > > > > > > > > > > > > > +static unsigned int num_io_queues;
> > > > > > > > > > > > > > +module_param_cb(num_io_queues, &queue_count_ops, &num_io_queues, 0644);
> > > > > > > > > > > > > > +MODULE_PARM_DESC(num_io_queues,
> > > > > > > > > > > > > > +		 "Number of IO virt queues to use for blk device. Should > 0");
> > > > > > > > > > better:
> > > > > > > > > > 
> > > > > > > > > > +MODULE_PARM_DESC(num_io_request_queues,
> > > > > > > > > > +                "Limit number of IO request virt queues to use for each device. 0 for now limit");
> > > > > > > > > You proposed it and I replied on it bellow.
> > > > > > > > Can't say I understand 100% what you are saying. Want to send
> > > > > > > > a description that does make sense to you but
> > > > > > > > also reflects reality? 0 is the default so
> > > > > > > > "should > 0" besides being ungrammatical does not seem t"
> > > > > > > > reflect what it does ...
> > > > > > > if you "modprobe virtio_blk" the previous behavior will happen.
> > > > > > > 
> > > > > > > You can't "modprobe virtio_blk num_io_request_queues=0" since the minimal
> > > > > > > value is 1.
> > > > > > > 
> > > > > > > So your description is not reflecting the code.
> > > > > > > 
> > > > > > > We can do:
> > > > > > > 
> > > > > > > MODULE_PARM_DESC(num_io_request_queues, "Number of request virt queues to use for blk device. Minimum value is 1 queue");
> > > > > > What's the default value? We should document that.
> > > > > default value for static global variables is 0.
> > > > > 
> > > > > MODULE_PARM_DESC(num_io_request_queues, "Number of request virt queues to
> > > > > use for blk device. Minimum value is 1 queue. Default and Maximum value is
> > > > > equal to the total number of CPUs");
> > > > So it says it's the # of cpus but yoiu inspect it with
> > > > sysfs and it's actually 0. Let's say that's confusing
> > > > at the least. why not just let users set it to 0
> > > > and document that?
> > > > 
> > > Setting it by the user to 0 makes no sense.
> > > 
> > > We can say "if not set, the value equals to the total number of CPUs".
> > the value is 0. it seems to mean "no limit". the actual # of queues is
> > then te smaller between # of cpus and # of hardware queues.
> > I see no reason not to allow user to set that especially if
> > it was originally the value then user changed it
> > and is trying to change it back.
> 
> I fine with that.
> 
> MODULE_PARM_DESC(num_io_request_queues, "Number of request virt queues to use for blk device. 0 value means no limitation");
> 

OK and the second distinction is that it's a limit on the
number, not the actual number. It's never more than what's provided
by the hypervisor.

> > 
> > > The actual value of the created queues can be seen in /sys/block/vda/mq/ as
> > > done today.
> > > > > > > > > > > > > > +
> > > > > > > > > > > > > >        static int major;
> > > > > > > > > > > > > >        static DEFINE_IDA(vd_index_ida);
> > > > > > > > > > > > > > @@ -501,7 +517,9 @@ static int init_vq(struct virtio_blk *vblk)
> > > > > > > > > > > > > >        	if (err)
> > > > > > > > > > > > > >        		num_vqs = 1;
> > > > > > > > > > > > > > -	num_vqs = min_t(unsigned int, nr_cpu_ids, num_vqs);
> > > > > > > > > > > > > > +	num_vqs = min_t(unsigned int,
> > > > > > > > > > > > > > +			min_not_zero(num_io_queues, nr_cpu_ids),
> > > > > > > > > > > > > > +			num_vqs);
> > > > > > > > > > > > > If you respin, please consider calling them request queues. That's the
> > > > > > > > > > > > > terminology from the VIRTIO spec and it's nice to keep it consistent.
> > > > > > > > > > > > > But the purpose of num_io_queues is clear, so:
> > > > > > > > > > > > > 
> > > > > > > > > > > > > Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> > > > > > > > > > > > I did this:
> > > > > > > > > > > > +static unsigned int num_io_request_queues;
> > > > > > > > > > > > +module_param_cb(num_io_request_queues, &queue_count_ops, &num_io_request_queues, 0644);
> > > > > > > > > > > > +MODULE_PARM_DESC(num_io_request_queues,
> > > > > > > > > > > > +                "Limit number of IO request virt queues to use for each device. 0 for now limit");
> > > > > > > > > > > The parameter is writable and can be changed and then new devices might be
> > > > > > > > > > > probed with new value.
> > > > > > > > > > > 
> > > > > > > > > > > It can't be zero in the code. we can change param_set_uint_minmax args and
> > > > > > > > > > > say that 0 says nr_cpus.
> > > > > > > > > > > 
> > > > > > > > > > > I'm ok with the renaming but I prefer to stick to the description we gave in
> > > > > > > > > > > V3 of this patch (and maybe enable value of 0 as mentioned above).

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Re: [PATCH v2 1/1] virtio-blk: add num_io_queues module parameter

[Max Gurtovoy]

On 9/12/2021 12:07 PM, Michael S. Tsirkin wrote:
> On Sat, Sep 11, 2021 at 03:56:45PM +0300, Max Gurtovoy wrote:
>> On 9/10/2021 1:57 AM, Michael S. Tsirkin wrote:
>>> On Thu, Sep 09, 2021 at 07:45:42PM +0300, Max Gurtovoy wrote:
>>>> On 9/9/2021 7:31 PM, Michael S. Tsirkin wrote:
>>>>> On Thu, Sep 09, 2021 at 06:51:56PM +0300, Max Gurtovoy wrote:
>>>>>> On 9/9/2021 6:40 PM, Michael S. Tsirkin wrote:
>>>>>>> On Thu, Sep 09, 2021 at 06:37:37PM +0300, Max Gurtovoy wrote:
>>>>>>>> On 9/9/2021 4:42 PM, Michael S. Tsirkin wrote:
>>>>>>>>> On Mon, Sep 06, 2021 at 02:59:40PM +0300, Max Gurtovoy wrote:
>>>>>>>>>> On 9/6/2021 2:20 PM, Michael S. Tsirkin wrote:
>>>>>>>>>>> On Mon, Sep 06, 2021 at 01:31:32AM +0300, Max Gurtovoy wrote:
>>>>>>>>>>>> On 9/5/2021 7:02 PM, Michael S. Tsirkin wrote:
>>>>>>>>>>>>> On Thu, Sep 02, 2021 at 02:45:52PM +0100, Stefan Hajnoczi wrote:
>>>>>>>>>>>>>> On Tue, Aug 31, 2021 at 04:50:35PM +0300, Max Gurtovoy wrote:
>>>>>>>>>>>>>>> Sometimes a user would like to control the amount of IO queues to be
>>>>>>>>>>>>>>> created for a block device. For example, for limiting the memory
>>>>>>>>>>>>>>> footprint of virtio-blk devices.
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
>>>>>>>>>>>>>>> ---
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> changes from v1:
>>>>>>>>>>>>>>>         - use param_set_uint_minmax (from Christoph)
>>>>>>>>>>>>>>>         - added "Should > 0" to module description
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> Note: This commit apply on top of Jens's branch for-5.15/drivers
>>>>>>>>>>>>>>> ---
>>>>>>>>>>>>>>>         drivers/block/virtio_blk.c | 20 +++++++++++++++++++-
>>>>>>>>>>>>>>>         1 file changed, 19 insertions(+), 1 deletion(-)
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
>>>>>>>>>>>>>>> index 4b49df2dfd23..9332fc4e9b31 100644
>>>>>>>>>>>>>>> --- a/drivers/block/virtio_blk.c
>>>>>>>>>>>>>>> +++ b/drivers/block/virtio_blk.c
>>>>>>>>>>>>>>> @@ -24,6 +24,22 @@
>>>>>>>>>>>>>>>         /* The maximum number of sg elements that fit into a virtqueue */
>>>>>>>>>>>>>>>         #define VIRTIO_BLK_MAX_SG_ELEMS 32768
>>>>>>>>>>>>>>> +static int virtblk_queue_count_set(const char *val,
>>>>>>>>>>>>>>> +		const struct kernel_param *kp)
>>>>>>>>>>>>>>> +{
>>>>>>>>>>>>>>> +	return param_set_uint_minmax(val, kp, 1, nr_cpu_ids);
>>>>>>>>>>>>>>> +}
>>>>>>>>>>> Hmm which tree is this for?
>>>>>>>>>> I've mentioned in the note that it apply on branch for-5.15/drivers. But now
>>>>>>>>>> you can apply it on linus/master as well.
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>> +static const struct kernel_param_ops queue_count_ops = {
>>>>>>>>>>>>>>> +	.set = virtblk_queue_count_set,
>>>>>>>>>>>>>>> +	.get = param_get_uint,
>>>>>>>>>>>>>>> +};
>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>> +static unsigned int num_io_queues;
>>>>>>>>>>>>>>> +module_param_cb(num_io_queues, &queue_count_ops, &num_io_queues, 0644);
>>>>>>>>>>>>>>> +MODULE_PARM_DESC(num_io_queues,
>>>>>>>>>>>>>>> +		 "Number of IO virt queues to use for blk device. Should > 0");
>>>>>>>>>>> better:
>>>>>>>>>>>
>>>>>>>>>>> +MODULE_PARM_DESC(num_io_request_queues,
>>>>>>>>>>> +                "Limit number of IO request virt queues to use for each device. 0 for now limit");
>>>>>>>>>> You proposed it and I replied on it bellow.
>>>>>>>>> Can't say I understand 100% what you are saying. Want to send
>>>>>>>>> a description that does make sense to you but
>>>>>>>>> also reflects reality? 0 is the default so
>>>>>>>>> "should > 0" besides being ungrammatical does not seem t"
>>>>>>>>> reflect what it does ...
>>>>>>>> if you "modprobe virtio_blk" the previous behavior will happen.
>>>>>>>>
>>>>>>>> You can't "modprobe virtio_blk num_io_request_queues=0" since the minimal
>>>>>>>> value is 1.
>>>>>>>>
>>>>>>>> So your description is not reflecting the code.
>>>>>>>>
>>>>>>>> We can do:
>>>>>>>>
>>>>>>>> MODULE_PARM_DESC(num_io_request_queues, "Number of request virt queues to use for blk device. Minimum value is 1 queue");
>>>>>>> What's the default value? We should document that.
>>>>>> default value for static global variables is 0.
>>>>>>
>>>>>> MODULE_PARM_DESC(num_io_request_queues, "Number of request virt queues to
>>>>>> use for blk device. Minimum value is 1 queue. Default and Maximum value is
>>>>>> equal to the total number of CPUs");
>>>>> So it says it's the # of cpus but yoiu inspect it with
>>>>> sysfs and it's actually 0. Let's say that's confusing
>>>>> at the least. why not just let users set it to 0
>>>>> and document that?
>>>>>
>>>> Setting it by the user to 0 makes no sense.
>>>>
>>>> We can say "if not set, the value equals to the total number of CPUs".
>>> the value is 0. it seems to mean "no limit". the actual # of queues is
>>> then te smaller between # of cpus and # of hardware queues.
>>> I see no reason not to allow user to set that especially if
>>> it was originally the value then user changed it
>>> and is trying to change it back.
>> I fine with that.
>>
>> MODULE_PARM_DESC(num_io_request_queues, "Number of request virt queues to use for blk device. 0 value means no limitation");
>>
> OK and the second distinction is that it's a limit on the
> number, not the actual number. It's never more than what's provided
> by the hypervisor.

MODULE_PARM_DESC(num_io_request_queues, "Maximal number of request virt queues to use for blk device. 0 value means no limitation");

is that ok ?

>>>> The actual value of the created queues can be seen in /sys/block/vda/mq/ as
>>>> done today.
>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>         static int major;
>>>>>>>>>>>>>>>         static DEFINE_IDA(vd_index_ida);
>>>>>>>>>>>>>>> @@ -501,7 +517,9 @@ static int init_vq(struct virtio_blk *vblk)
>>>>>>>>>>>>>>>         	if (err)
>>>>>>>>>>>>>>>         		num_vqs = 1;
>>>>>>>>>>>>>>> -	num_vqs = min_t(unsigned int, nr_cpu_ids, num_vqs);
>>>>>>>>>>>>>>> +	num_vqs = min_t(unsigned int,
>>>>>>>>>>>>>>> +			min_not_zero(num_io_queues, nr_cpu_ids),
>>>>>>>>>>>>>>> +			num_vqs);
>>>>>>>>>>>>>> If you respin, please consider calling them request queues. That's the
>>>>>>>>>>>>>> terminology from the VIRTIO spec and it's nice to keep it consistent.
>>>>>>>>>>>>>> But the purpose of num_io_queues is clear, so:
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
>>>>>>>>>>>>> I did this:
>>>>>>>>>>>>> +static unsigned int num_io_request_queues;
>>>>>>>>>>>>> +module_param_cb(num_io_request_queues, &queue_count_ops, &num_io_request_queues, 0644);
>>>>>>>>>>>>> +MODULE_PARM_DESC(num_io_request_queues,
>>>>>>>>>>>>> +                "Limit number of IO request virt queues to use for each device. 0 for now limit");
>>>>>>>>>>>> The parameter is writable and can be changed and then new devices might be
>>>>>>>>>>>> probed with new value.
>>>>>>>>>>>>
>>>>>>>>>>>> It can't be zero in the code. we can change param_set_uint_minmax args and
>>>>>>>>>>>> say that 0 says nr_cpus.
>>>>>>>>>>>>
>>>>>>>>>>>> I'm ok with the renaming but I prefer to stick to the description we gave in
>>>>>>>>>>>> V3 of this patch (and maybe enable value of 0 as mentioned above).

Re: [PATCH v2 1/1] virtio-blk: add num_io_queues module parameter

[Michael S. Tsirkin]

On Sun, Sep 12, 2021 at 12:37:26PM +0300, Max Gurtovoy wrote:
> 
> On 9/12/2021 12:07 PM, Michael S. Tsirkin wrote:
> > On Sat, Sep 11, 2021 at 03:56:45PM +0300, Max Gurtovoy wrote:
> > > On 9/10/2021 1:57 AM, Michael S. Tsirkin wrote:
> > > > On Thu, Sep 09, 2021 at 07:45:42PM +0300, Max Gurtovoy wrote:
> > > > > On 9/9/2021 7:31 PM, Michael S. Tsirkin wrote:
> > > > > > On Thu, Sep 09, 2021 at 06:51:56PM +0300, Max Gurtovoy wrote:
> > > > > > > On 9/9/2021 6:40 PM, Michael S. Tsirkin wrote:
> > > > > > > > On Thu, Sep 09, 2021 at 06:37:37PM +0300, Max Gurtovoy wrote:
> > > > > > > > > On 9/9/2021 4:42 PM, Michael S. Tsirkin wrote:
> > > > > > > > > > On Mon, Sep 06, 2021 at 02:59:40PM +0300, Max Gurtovoy wrote:
> > > > > > > > > > > On 9/6/2021 2:20 PM, Michael S. Tsirkin wrote:
> > > > > > > > > > > > On Mon, Sep 06, 2021 at 01:31:32AM +0300, Max Gurtovoy wrote:
> > > > > > > > > > > > > On 9/5/2021 7:02 PM, Michael S. Tsirkin wrote:
> > > > > > > > > > > > > > On Thu, Sep 02, 2021 at 02:45:52PM +0100, Stefan Hajnoczi wrote:
> > > > > > > > > > > > > > > On Tue, Aug 31, 2021 at 04:50:35PM +0300, Max Gurtovoy wrote:
> > > > > > > > > > > > > > > > Sometimes a user would like to control the amount of IO queues to be
> > > > > > > > > > > > > > > > created for a block device. For example, for limiting the memory
> > > > > > > > > > > > > > > > footprint of virtio-blk devices.
> > > > > > > > > > > > > > > > 
> > > > > > > > > > > > > > > > Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
> > > > > > > > > > > > > > > > ---
> > > > > > > > > > > > > > > > 
> > > > > > > > > > > > > > > > changes from v1:
> > > > > > > > > > > > > > > >         - use param_set_uint_minmax (from Christoph)
> > > > > > > > > > > > > > > >         - added "Should > 0" to module description
> > > > > > > > > > > > > > > > 
> > > > > > > > > > > > > > > > Note: This commit apply on top of Jens's branch for-5.15/drivers
> > > > > > > > > > > > > > > > ---
> > > > > > > > > > > > > > > >         drivers/block/virtio_blk.c | 20 +++++++++++++++++++-
> > > > > > > > > > > > > > > >         1 file changed, 19 insertions(+), 1 deletion(-)
> > > > > > > > > > > > > > > > 
> > > > > > > > > > > > > > > > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> > > > > > > > > > > > > > > > index 4b49df2dfd23..9332fc4e9b31 100644
> > > > > > > > > > > > > > > > --- a/drivers/block/virtio_blk.c
> > > > > > > > > > > > > > > > +++ b/drivers/block/virtio_blk.c
> > > > > > > > > > > > > > > > @@ -24,6 +24,22 @@
> > > > > > > > > > > > > > > >         /* The maximum number of sg elements that fit into a virtqueue */
> > > > > > > > > > > > > > > >         #define VIRTIO_BLK_MAX_SG_ELEMS 32768
> > > > > > > > > > > > > > > > +static int virtblk_queue_count_set(const char *val,
> > > > > > > > > > > > > > > > +		const struct kernel_param *kp)
> > > > > > > > > > > > > > > > +{
> > > > > > > > > > > > > > > > +	return param_set_uint_minmax(val, kp, 1, nr_cpu_ids);
> > > > > > > > > > > > > > > > +}
> > > > > > > > > > > > Hmm which tree is this for?
> > > > > > > > > > > I've mentioned in the note that it apply on branch for-5.15/drivers. But now
> > > > > > > > > > > you can apply it on linus/master as well.
> > > > > > > > > > > 
> > > > > > > > > > > 
> > > > > > > > > > > > > > > > +
> > > > > > > > > > > > > > > > +static const struct kernel_param_ops queue_count_ops = {
> > > > > > > > > > > > > > > > +	.set = virtblk_queue_count_set,
> > > > > > > > > > > > > > > > +	.get = param_get_uint,
> > > > > > > > > > > > > > > > +};
> > > > > > > > > > > > > > > > +
> > > > > > > > > > > > > > > > +static unsigned int num_io_queues;
> > > > > > > > > > > > > > > > +module_param_cb(num_io_queues, &queue_count_ops, &num_io_queues, 0644);
> > > > > > > > > > > > > > > > +MODULE_PARM_DESC(num_io_queues,
> > > > > > > > > > > > > > > > +		 "Number of IO virt queues to use for blk device. Should > 0");
> > > > > > > > > > > > better:
> > > > > > > > > > > > 
> > > > > > > > > > > > +MODULE_PARM_DESC(num_io_request_queues,
> > > > > > > > > > > > +                "Limit number of IO request virt queues to use for each device. 0 for now limit");
> > > > > > > > > > > You proposed it and I replied on it bellow.
> > > > > > > > > > Can't say I understand 100% what you are saying. Want to send
> > > > > > > > > > a description that does make sense to you but
> > > > > > > > > > also reflects reality? 0 is the default so
> > > > > > > > > > "should > 0" besides being ungrammatical does not seem t"
> > > > > > > > > > reflect what it does ...
> > > > > > > > > if you "modprobe virtio_blk" the previous behavior will happen.
> > > > > > > > > 
> > > > > > > > > You can't "modprobe virtio_blk num_io_request_queues=0" since the minimal
> > > > > > > > > value is 1.
> > > > > > > > > 
> > > > > > > > > So your description is not reflecting the code.
> > > > > > > > > 
> > > > > > > > > We can do:
> > > > > > > > > 
> > > > > > > > > MODULE_PARM_DESC(num_io_request_queues, "Number of request virt queues to use for blk device. Minimum value is 1 queue");
> > > > > > > > What's the default value? We should document that.
> > > > > > > default value for static global variables is 0.
> > > > > > > 
> > > > > > > MODULE_PARM_DESC(num_io_request_queues, "Number of request virt queues to
> > > > > > > use for blk device. Minimum value is 1 queue. Default and Maximum value is
> > > > > > > equal to the total number of CPUs");
> > > > > > So it says it's the # of cpus but yoiu inspect it with
> > > > > > sysfs and it's actually 0. Let's say that's confusing
> > > > > > at the least. why not just let users set it to 0
> > > > > > and document that?
> > > > > > 
> > > > > Setting it by the user to 0 makes no sense.
> > > > > 
> > > > > We can say "if not set, the value equals to the total number of CPUs".
> > > > the value is 0. it seems to mean "no limit". the actual # of queues is
> > > > then te smaller between # of cpus and # of hardware queues.
> > > > I see no reason not to allow user to set that especially if
> > > > it was originally the value then user changed it
> > > > and is trying to change it back.
> > > I fine with that.
> > > 
> > > MODULE_PARM_DESC(num_io_request_queues, "Number of request virt queues to use for blk device. 0 value means no limitation");
> > > 
> > OK and the second distinction is that it's a limit on the
> > number, not the actual number. It's never more than what's provided
> > by the hypervisor.
> 
> MODULE_PARM_DESC(num_io_request_queues, "Maximal number of request virt queues to use for blk device. 0 value means no limitation");
> 
> is that ok ?


Looks ok. And then do we need to limit this to nr_cpu_ids?
Setting a value that's too high seems harmless ...

> > > > > The actual value of the created queues can be seen in /sys/block/vda/mq/ as
> > > > > done today.
> > > > > > > > > > > > > > > > +
> > > > > > > > > > > > > > > >         static int major;
> > > > > > > > > > > > > > > >         static DEFINE_IDA(vd_index_ida);
> > > > > > > > > > > > > > > > @@ -501,7 +517,9 @@ static int init_vq(struct virtio_blk *vblk)
> > > > > > > > > > > > > > > >         	if (err)
> > > > > > > > > > > > > > > >         		num_vqs = 1;
> > > > > > > > > > > > > > > > -	num_vqs = min_t(unsigned int, nr_cpu_ids, num_vqs);
> > > > > > > > > > > > > > > > +	num_vqs = min_t(unsigned int,
> > > > > > > > > > > > > > > > +			min_not_zero(num_io_queues, nr_cpu_ids),
> > > > > > > > > > > > > > > > +			num_vqs);
> > > > > > > > > > > > > > > If you respin, please consider calling them request queues. That's the
> > > > > > > > > > > > > > > terminology from the VIRTIO spec and it's nice to keep it consistent.
> > > > > > > > > > > > > > > But the purpose of num_io_queues is clear, so:
> > > > > > > > > > > > > > > 
> > > > > > > > > > > > > > > Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> > > > > > > > > > > > > > I did this:
> > > > > > > > > > > > > > +static unsigned int num_io_request_queues;
> > > > > > > > > > > > > > +module_param_cb(num_io_request_queues, &queue_count_ops, &num_io_request_queues, 0644);
> > > > > > > > > > > > > > +MODULE_PARM_DESC(num_io_request_queues,
> > > > > > > > > > > > > > +                "Limit number of IO request virt queues to use for each device. 0 for now limit");
> > > > > > > > > > > > > The parameter is writable and can be changed and then new devices might be
> > > > > > > > > > > > > probed with new value.
> > > > > > > > > > > > > 
> > > > > > > > > > > > > It can't be zero in the code. we can change param_set_uint_minmax args and
> > > > > > > > > > > > > say that 0 says nr_cpus.
> > > > > > > > > > > > > 
> > > > > > > > > > > > > I'm ok with the renaming but I prefer to stick to the description we gave in
> > > > > > > > > > > > > V3 of this patch (and maybe enable value of 0 as mentioned above).

Re: [PATCH v2 1/1] virtio-blk: add num_io_queues module parameter

[Michael S. Tsirkin]

On Sun, Sep 12, 2021 at 12:37:26PM +0300, Max Gurtovoy wrote:
> 
> On 9/12/2021 12:07 PM, Michael S. Tsirkin wrote:
> > On Sat, Sep 11, 2021 at 03:56:45PM +0300, Max Gurtovoy wrote:
> > > On 9/10/2021 1:57 AM, Michael S. Tsirkin wrote:
> > > > On Thu, Sep 09, 2021 at 07:45:42PM +0300, Max Gurtovoy wrote:
> > > > > On 9/9/2021 7:31 PM, Michael S. Tsirkin wrote:
> > > > > > On Thu, Sep 09, 2021 at 06:51:56PM +0300, Max Gurtovoy wrote:
> > > > > > > On 9/9/2021 6:40 PM, Michael S. Tsirkin wrote:
> > > > > > > > On Thu, Sep 09, 2021 at 06:37:37PM +0300, Max Gurtovoy wrote:
> > > > > > > > > On 9/9/2021 4:42 PM, Michael S. Tsirkin wrote:
> > > > > > > > > > On Mon, Sep 06, 2021 at 02:59:40PM +0300, Max Gurtovoy wrote:
> > > > > > > > > > > On 9/6/2021 2:20 PM, Michael S. Tsirkin wrote:
> > > > > > > > > > > > On Mon, Sep 06, 2021 at 01:31:32AM +0300, Max Gurtovoy wrote:
> > > > > > > > > > > > > On 9/5/2021 7:02 PM, Michael S. Tsirkin wrote:
> > > > > > > > > > > > > > On Thu, Sep 02, 2021 at 02:45:52PM +0100, Stefan Hajnoczi wrote:
> > > > > > > > > > > > > > > On Tue, Aug 31, 2021 at 04:50:35PM +0300, Max Gurtovoy wrote:
> > > > > > > > > > > > > > > > Sometimes a user would like to control the amount of IO queues to be
> > > > > > > > > > > > > > > > created for a block device. For example, for limiting the memory
> > > > > > > > > > > > > > > > footprint of virtio-blk devices.
> > > > > > > > > > > > > > > > 
> > > > > > > > > > > > > > > > Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
> > > > > > > > > > > > > > > > ---
> > > > > > > > > > > > > > > > 
> > > > > > > > > > > > > > > > changes from v1:
> > > > > > > > > > > > > > > >         - use param_set_uint_minmax (from Christoph)
> > > > > > > > > > > > > > > >         - added "Should > 0" to module description
> > > > > > > > > > > > > > > > 
> > > > > > > > > > > > > > > > Note: This commit apply on top of Jens's branch for-5.15/drivers
> > > > > > > > > > > > > > > > ---
> > > > > > > > > > > > > > > >         drivers/block/virtio_blk.c | 20 +++++++++++++++++++-
> > > > > > > > > > > > > > > >         1 file changed, 19 insertions(+), 1 deletion(-)
> > > > > > > > > > > > > > > > 
> > > > > > > > > > > > > > > > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> > > > > > > > > > > > > > > > index 4b49df2dfd23..9332fc4e9b31 100644
> > > > > > > > > > > > > > > > --- a/drivers/block/virtio_blk.c
> > > > > > > > > > > > > > > > +++ b/drivers/block/virtio_blk.c
> > > > > > > > > > > > > > > > @@ -24,6 +24,22 @@
> > > > > > > > > > > > > > > >         /* The maximum number of sg elements that fit into a virtqueue */
> > > > > > > > > > > > > > > >         #define VIRTIO_BLK_MAX_SG_ELEMS 32768
> > > > > > > > > > > > > > > > +static int virtblk_queue_count_set(const char *val,
> > > > > > > > > > > > > > > > +		const struct kernel_param *kp)
> > > > > > > > > > > > > > > > +{
> > > > > > > > > > > > > > > > +	return param_set_uint_minmax(val, kp, 1, nr_cpu_ids);
> > > > > > > > > > > > > > > > +}
> > > > > > > > > > > > Hmm which tree is this for?
> > > > > > > > > > > I've mentioned in the note that it apply on branch for-5.15/drivers. But now
> > > > > > > > > > > you can apply it on linus/master as well.
> > > > > > > > > > > 
> > > > > > > > > > > 
> > > > > > > > > > > > > > > > +
> > > > > > > > > > > > > > > > +static const struct kernel_param_ops queue_count_ops = {
> > > > > > > > > > > > > > > > +	.set = virtblk_queue_count_set,
> > > > > > > > > > > > > > > > +	.get = param_get_uint,
> > > > > > > > > > > > > > > > +};
> > > > > > > > > > > > > > > > +
> > > > > > > > > > > > > > > > +static unsigned int num_io_queues;
> > > > > > > > > > > > > > > > +module_param_cb(num_io_queues, &queue_count_ops, &num_io_queues, 0644);
> > > > > > > > > > > > > > > > +MODULE_PARM_DESC(num_io_queues,
> > > > > > > > > > > > > > > > +		 "Number of IO virt queues to use for blk device. Should > 0");
> > > > > > > > > > > > better:
> > > > > > > > > > > > 
> > > > > > > > > > > > +MODULE_PARM_DESC(num_io_request_queues,
> > > > > > > > > > > > +                "Limit number of IO request virt queues to use for each device. 0 for now limit");
> > > > > > > > > > > You proposed it and I replied on it bellow.
> > > > > > > > > > Can't say I understand 100% what you are saying. Want to send
> > > > > > > > > > a description that does make sense to you but
> > > > > > > > > > also reflects reality? 0 is the default so
> > > > > > > > > > "should > 0" besides being ungrammatical does not seem t"
> > > > > > > > > > reflect what it does ...
> > > > > > > > > if you "modprobe virtio_blk" the previous behavior will happen.
> > > > > > > > > 
> > > > > > > > > You can't "modprobe virtio_blk num_io_request_queues=0" since the minimal
> > > > > > > > > value is 1.
> > > > > > > > > 
> > > > > > > > > So your description is not reflecting the code.
> > > > > > > > > 
> > > > > > > > > We can do:
> > > > > > > > > 
> > > > > > > > > MODULE_PARM_DESC(num_io_request_queues, "Number of request virt queues to use for blk device. Minimum value is 1 queue");
> > > > > > > > What's the default value? We should document that.
> > > > > > > default value for static global variables is 0.
> > > > > > > 
> > > > > > > MODULE_PARM_DESC(num_io_request_queues, "Number of request virt queues to
> > > > > > > use for blk device. Minimum value is 1 queue. Default and Maximum value is
> > > > > > > equal to the total number of CPUs");
> > > > > > So it says it's the # of cpus but yoiu inspect it with
> > > > > > sysfs and it's actually 0. Let's say that's confusing
> > > > > > at the least. why not just let users set it to 0
> > > > > > and document that?
> > > > > > 
> > > > > Setting it by the user to 0 makes no sense.
> > > > > 
> > > > > We can say "if not set, the value equals to the total number of CPUs".
> > > > the value is 0. it seems to mean "no limit". the actual # of queues is
> > > > then te smaller between # of cpus and # of hardware queues.
> > > > I see no reason not to allow user to set that especially if
> > > > it was originally the value then user changed it
> > > > and is trying to change it back.
> > > I fine with that.
> > > 
> > > MODULE_PARM_DESC(num_io_request_queues, "Number of request virt queues to use for blk device. 0 value means no limitation");
> > > 
> > OK and the second distinction is that it's a limit on the
> > number, not the actual number. It's never more than what's provided
> > by the hypervisor.
> 
> MODULE_PARM_DESC(num_io_request_queues, "Maximal number of request virt queues to use for blk device. 0 value means no limitation");
> 
> is that ok ?


Looks ok. And then do we need to limit this to nr_cpu_ids?
Setting a value that's too high seems harmless ...

> > > > > The actual value of the created queues can be seen in /sys/block/vda/mq/ as
> > > > > done today.
> > > > > > > > > > > > > > > > +
> > > > > > > > > > > > > > > >         static int major;
> > > > > > > > > > > > > > > >         static DEFINE_IDA(vd_index_ida);
> > > > > > > > > > > > > > > > @@ -501,7 +517,9 @@ static int init_vq(struct virtio_blk *vblk)
> > > > > > > > > > > > > > > >         	if (err)
> > > > > > > > > > > > > > > >         		num_vqs = 1;
> > > > > > > > > > > > > > > > -	num_vqs = min_t(unsigned int, nr_cpu_ids, num_vqs);
> > > > > > > > > > > > > > > > +	num_vqs = min_t(unsigned int,
> > > > > > > > > > > > > > > > +			min_not_zero(num_io_queues, nr_cpu_ids),
> > > > > > > > > > > > > > > > +			num_vqs);
> > > > > > > > > > > > > > > If you respin, please consider calling them request queues. That's the
> > > > > > > > > > > > > > > terminology from the VIRTIO spec and it's nice to keep it consistent.
> > > > > > > > > > > > > > > But the purpose of num_io_queues is clear, so:
> > > > > > > > > > > > > > > 
> > > > > > > > > > > > > > > Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> > > > > > > > > > > > > > I did this:
> > > > > > > > > > > > > > +static unsigned int num_io_request_queues;
> > > > > > > > > > > > > > +module_param_cb(num_io_request_queues, &queue_count_ops, &num_io_request_queues, 0644);
> > > > > > > > > > > > > > +MODULE_PARM_DESC(num_io_request_queues,
> > > > > > > > > > > > > > +                "Limit number of IO request virt queues to use for each device. 0 for now limit");
> > > > > > > > > > > > > The parameter is writable and can be changed and then new devices might be
> > > > > > > > > > > > > probed with new value.
> > > > > > > > > > > > > 
> > > > > > > > > > > > > It can't be zero in the code. we can change param_set_uint_minmax args and
> > > > > > > > > > > > > say that 0 says nr_cpus.
> > > > > > > > > > > > > 
> > > > > > > > > > > > > I'm ok with the renaming but I prefer to stick to the description we gave in
> > > > > > > > > > > > > V3 of this patch (and maybe enable value of 0 as mentioned above).

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Re: [PATCH v2 1/1] virtio-blk: add num_io_queues module parameter

[Max Gurtovoy]

On 9/12/2021 12:50 PM, Michael S. Tsirkin wrote:
> On Sun, Sep 12, 2021 at 12:37:26PM +0300, Max Gurtovoy wrote:
>> On 9/12/2021 12:07 PM, Michael S. Tsirkin wrote:
>>> On Sat, Sep 11, 2021 at 03:56:45PM +0300, Max Gurtovoy wrote:
>>>> On 9/10/2021 1:57 AM, Michael S. Tsirkin wrote:
>>>>> On Thu, Sep 09, 2021 at 07:45:42PM +0300, Max Gurtovoy wrote:
>>>>>> On 9/9/2021 7:31 PM, Michael S. Tsirkin wrote:
>>>>>>> On Thu, Sep 09, 2021 at 06:51:56PM +0300, Max Gurtovoy wrote:
>>>>>>>> On 9/9/2021 6:40 PM, Michael S. Tsirkin wrote:
>>>>>>>>> On Thu, Sep 09, 2021 at 06:37:37PM +0300, Max Gurtovoy wrote:
>>>>>>>>>> On 9/9/2021 4:42 PM, Michael S. Tsirkin wrote:
>>>>>>>>>>> On Mon, Sep 06, 2021 at 02:59:40PM +0300, Max Gurtovoy wrote:
>>>>>>>>>>>> On 9/6/2021 2:20 PM, Michael S. Tsirkin wrote:
>>>>>>>>>>>>> On Mon, Sep 06, 2021 at 01:31:32AM +0300, Max Gurtovoy wrote:
>>>>>>>>>>>>>> On 9/5/2021 7:02 PM, Michael S. Tsirkin wrote:
>>>>>>>>>>>>>>> On Thu, Sep 02, 2021 at 02:45:52PM +0100, Stefan Hajnoczi wrote:
>>>>>>>>>>>>>>>> On Tue, Aug 31, 2021 at 04:50:35PM +0300, Max Gurtovoy wrote:
>>>>>>>>>>>>>>>>> Sometimes a user would like to control the amount of IO queues to be
>>>>>>>>>>>>>>>>> created for a block device. For example, for limiting the memory
>>>>>>>>>>>>>>>>> footprint of virtio-blk devices.
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>> Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
>>>>>>>>>>>>>>>>> ---
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>> changes from v1:
>>>>>>>>>>>>>>>>>          - use param_set_uint_minmax (from Christoph)
>>>>>>>>>>>>>>>>>          - added "Should > 0" to module description
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>> Note: This commit apply on top of Jens's branch for-5.15/drivers
>>>>>>>>>>>>>>>>> ---
>>>>>>>>>>>>>>>>>          drivers/block/virtio_blk.c | 20 +++++++++++++++++++-
>>>>>>>>>>>>>>>>>          1 file changed, 19 insertions(+), 1 deletion(-)
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
>>>>>>>>>>>>>>>>> index 4b49df2dfd23..9332fc4e9b31 100644
>>>>>>>>>>>>>>>>> --- a/drivers/block/virtio_blk.c
>>>>>>>>>>>>>>>>> +++ b/drivers/block/virtio_blk.c
>>>>>>>>>>>>>>>>> @@ -24,6 +24,22 @@
>>>>>>>>>>>>>>>>>          /* The maximum number of sg elements that fit into a virtqueue */
>>>>>>>>>>>>>>>>>          #define VIRTIO_BLK_MAX_SG_ELEMS 32768
>>>>>>>>>>>>>>>>> +static int virtblk_queue_count_set(const char *val,
>>>>>>>>>>>>>>>>> +		const struct kernel_param *kp)
>>>>>>>>>>>>>>>>> +{
>>>>>>>>>>>>>>>>> +	return param_set_uint_minmax(val, kp, 1, nr_cpu_ids);
>>>>>>>>>>>>>>>>> +}
>>>>>>>>>>>>> Hmm which tree is this for?
>>>>>>>>>>>> I've mentioned in the note that it apply on branch for-5.15/drivers. But now
>>>>>>>>>>>> you can apply it on linus/master as well.
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>>> +static const struct kernel_param_ops queue_count_ops = {
>>>>>>>>>>>>>>>>> +	.set = virtblk_queue_count_set,
>>>>>>>>>>>>>>>>> +	.get = param_get_uint,
>>>>>>>>>>>>>>>>> +};
>>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>>> +static unsigned int num_io_queues;
>>>>>>>>>>>>>>>>> +module_param_cb(num_io_queues, &queue_count_ops, &num_io_queues, 0644);
>>>>>>>>>>>>>>>>> +MODULE_PARM_DESC(num_io_queues,
>>>>>>>>>>>>>>>>> +		 "Number of IO virt queues to use for blk device. Should > 0");
>>>>>>>>>>>>> better:
>>>>>>>>>>>>>
>>>>>>>>>>>>> +MODULE_PARM_DESC(num_io_request_queues,
>>>>>>>>>>>>> +                "Limit number of IO request virt queues to use for each device. 0 for now limit");
>>>>>>>>>>>> You proposed it and I replied on it bellow.
>>>>>>>>>>> Can't say I understand 100% what you are saying. Want to send
>>>>>>>>>>> a description that does make sense to you but
>>>>>>>>>>> also reflects reality? 0 is the default so
>>>>>>>>>>> "should > 0" besides being ungrammatical does not seem t"
>>>>>>>>>>> reflect what it does ...
>>>>>>>>>> if you "modprobe virtio_blk" the previous behavior will happen.
>>>>>>>>>>
>>>>>>>>>> You can't "modprobe virtio_blk num_io_request_queues=0" since the minimal
>>>>>>>>>> value is 1.
>>>>>>>>>>
>>>>>>>>>> So your description is not reflecting the code.
>>>>>>>>>>
>>>>>>>>>> We can do:
>>>>>>>>>>
>>>>>>>>>> MODULE_PARM_DESC(num_io_request_queues, "Number of request virt queues to use for blk device. Minimum value is 1 queue");
>>>>>>>>> What's the default value? We should document that.
>>>>>>>> default value for static global variables is 0.
>>>>>>>>
>>>>>>>> MODULE_PARM_DESC(num_io_request_queues, "Number of request virt queues to
>>>>>>>> use for blk device. Minimum value is 1 queue. Default and Maximum value is
>>>>>>>> equal to the total number of CPUs");
>>>>>>> So it says it's the # of cpus but yoiu inspect it with
>>>>>>> sysfs and it's actually 0. Let's say that's confusing
>>>>>>> at the least. why not just let users set it to 0
>>>>>>> and document that?
>>>>>>>
>>>>>> Setting it by the user to 0 makes no sense.
>>>>>>
>>>>>> We can say "if not set, the value equals to the total number of CPUs".
>>>>> the value is 0. it seems to mean "no limit". the actual # of queues is
>>>>> then te smaller between # of cpus and # of hardware queues.
>>>>> I see no reason not to allow user to set that especially if
>>>>> it was originally the value then user changed it
>>>>> and is trying to change it back.
>>>> I fine with that.
>>>>
>>>> MODULE_PARM_DESC(num_io_request_queues, "Number of request virt queues to use for blk device. 0 value means no limitation");
>>>>
>>> OK and the second distinction is that it's a limit on the
>>> number, not the actual number. It's never more than what's provided
>>> by the hypervisor.
>> MODULE_PARM_DESC(num_io_request_queues, "Maximal number of request virt queues to use for blk device. 0 value means no limitation");
>>
>> is that ok ?
>
> Looks ok. And then do we need to limit this to nr_cpu_ids?
> Setting a value that's too high seems harmless ...

why would you want that ?


>
>>>>>> The actual value of the created queues can be seen in /sys/block/vda/mq/ as
>>>>>> done today.
>>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>>>          static int major;
>>>>>>>>>>>>>>>>>          static DEFINE_IDA(vd_index_ida);
>>>>>>>>>>>>>>>>> @@ -501,7 +517,9 @@ static int init_vq(struct virtio_blk *vblk)
>>>>>>>>>>>>>>>>>          	if (err)
>>>>>>>>>>>>>>>>>          		num_vqs = 1;
>>>>>>>>>>>>>>>>> -	num_vqs = min_t(unsigned int, nr_cpu_ids, num_vqs);
>>>>>>>>>>>>>>>>> +	num_vqs = min_t(unsigned int,
>>>>>>>>>>>>>>>>> +			min_not_zero(num_io_queues, nr_cpu_ids),
>>>>>>>>>>>>>>>>> +			num_vqs);
>>>>>>>>>>>>>>>> If you respin, please consider calling them request queues. That's the
>>>>>>>>>>>>>>>> terminology from the VIRTIO spec and it's nice to keep it consistent.
>>>>>>>>>>>>>>>> But the purpose of num_io_queues is clear, so:
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
>>>>>>>>>>>>>>> I did this:
>>>>>>>>>>>>>>> +static unsigned int num_io_request_queues;
>>>>>>>>>>>>>>> +module_param_cb(num_io_request_queues, &queue_count_ops, &num_io_request_queues, 0644);
>>>>>>>>>>>>>>> +MODULE_PARM_DESC(num_io_request_queues,
>>>>>>>>>>>>>>> +                "Limit number of IO request virt queues to use for each device. 0 for now limit");
>>>>>>>>>>>>>> The parameter is writable and can be changed and then new devices might be
>>>>>>>>>>>>>> probed with new value.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> It can't be zero in the code. we can change param_set_uint_minmax args and
>>>>>>>>>>>>>> say that 0 says nr_cpus.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> I'm ok with the renaming but I prefer to stick to the description we gave in
>>>>>>>>>>>>>> V3 of this patch (and maybe enable value of 0 as mentioned above).

Re: [PATCH v2 1/1] virtio-blk: add num_io_queues module parameter

[Michael S. Tsirkin]

On Sun, Sep 12, 2021 at 01:33:13PM +0300, Max Gurtovoy wrote:
> 
> On 9/12/2021 12:50 PM, Michael S. Tsirkin wrote:
> > On Sun, Sep 12, 2021 at 12:37:26PM +0300, Max Gurtovoy wrote:
> > > On 9/12/2021 12:07 PM, Michael S. Tsirkin wrote:
> > > > On Sat, Sep 11, 2021 at 03:56:45PM +0300, Max Gurtovoy wrote:
> > > > > On 9/10/2021 1:57 AM, Michael S. Tsirkin wrote:
> > > > > > On Thu, Sep 09, 2021 at 07:45:42PM +0300, Max Gurtovoy wrote:
> > > > > > > On 9/9/2021 7:31 PM, Michael S. Tsirkin wrote:
> > > > > > > > On Thu, Sep 09, 2021 at 06:51:56PM +0300, Max Gurtovoy wrote:
> > > > > > > > > On 9/9/2021 6:40 PM, Michael S. Tsirkin wrote:
> > > > > > > > > > On Thu, Sep 09, 2021 at 06:37:37PM +0300, Max Gurtovoy wrote:
> > > > > > > > > > > On 9/9/2021 4:42 PM, Michael S. Tsirkin wrote:
> > > > > > > > > > > > On Mon, Sep 06, 2021 at 02:59:40PM +0300, Max Gurtovoy wrote:
> > > > > > > > > > > > > On 9/6/2021 2:20 PM, Michael S. Tsirkin wrote:
> > > > > > > > > > > > > > On Mon, Sep 06, 2021 at 01:31:32AM +0300, Max Gurtovoy wrote:
> > > > > > > > > > > > > > > On 9/5/2021 7:02 PM, Michael S. Tsirkin wrote:
> > > > > > > > > > > > > > > > On Thu, Sep 02, 2021 at 02:45:52PM +0100, Stefan Hajnoczi wrote:
> > > > > > > > > > > > > > > > > On Tue, Aug 31, 2021 at 04:50:35PM +0300, Max Gurtovoy wrote:
> > > > > > > > > > > > > > > > > > Sometimes a user would like to control the amount of IO queues to be
> > > > > > > > > > > > > > > > > > created for a block device. For example, for limiting the memory
> > > > > > > > > > > > > > > > > > footprint of virtio-blk devices.
> > > > > > > > > > > > > > > > > > 
> > > > > > > > > > > > > > > > > > Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
> > > > > > > > > > > > > > > > > > ---
> > > > > > > > > > > > > > > > > > 
> > > > > > > > > > > > > > > > > > changes from v1:
> > > > > > > > > > > > > > > > > >          - use param_set_uint_minmax (from Christoph)
> > > > > > > > > > > > > > > > > >          - added "Should > 0" to module description
> > > > > > > > > > > > > > > > > > 
> > > > > > > > > > > > > > > > > > Note: This commit apply on top of Jens's branch for-5.15/drivers
> > > > > > > > > > > > > > > > > > ---
> > > > > > > > > > > > > > > > > >          drivers/block/virtio_blk.c | 20 +++++++++++++++++++-
> > > > > > > > > > > > > > > > > >          1 file changed, 19 insertions(+), 1 deletion(-)
> > > > > > > > > > > > > > > > > > 
> > > > > > > > > > > > > > > > > > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> > > > > > > > > > > > > > > > > > index 4b49df2dfd23..9332fc4e9b31 100644
> > > > > > > > > > > > > > > > > > --- a/drivers/block/virtio_blk.c
> > > > > > > > > > > > > > > > > > +++ b/drivers/block/virtio_blk.c
> > > > > > > > > > > > > > > > > > @@ -24,6 +24,22 @@
> > > > > > > > > > > > > > > > > >          /* The maximum number of sg elements that fit into a virtqueue */
> > > > > > > > > > > > > > > > > >          #define VIRTIO_BLK_MAX_SG_ELEMS 32768
> > > > > > > > > > > > > > > > > > +static int virtblk_queue_count_set(const char *val,
> > > > > > > > > > > > > > > > > > +		const struct kernel_param *kp)
> > > > > > > > > > > > > > > > > > +{
> > > > > > > > > > > > > > > > > > +	return param_set_uint_minmax(val, kp, 1, nr_cpu_ids);
> > > > > > > > > > > > > > > > > > +}
> > > > > > > > > > > > > > Hmm which tree is this for?
> > > > > > > > > > > > > I've mentioned in the note that it apply on branch for-5.15/drivers. But now
> > > > > > > > > > > > > you can apply it on linus/master as well.
> > > > > > > > > > > > > 
> > > > > > > > > > > > > 
> > > > > > > > > > > > > > > > > > +
> > > > > > > > > > > > > > > > > > +static const struct kernel_param_ops queue_count_ops = {
> > > > > > > > > > > > > > > > > > +	.set = virtblk_queue_count_set,
> > > > > > > > > > > > > > > > > > +	.get = param_get_uint,
> > > > > > > > > > > > > > > > > > +};
> > > > > > > > > > > > > > > > > > +
> > > > > > > > > > > > > > > > > > +static unsigned int num_io_queues;
> > > > > > > > > > > > > > > > > > +module_param_cb(num_io_queues, &queue_count_ops, &num_io_queues, 0644);
> > > > > > > > > > > > > > > > > > +MODULE_PARM_DESC(num_io_queues,
> > > > > > > > > > > > > > > > > > +		 "Number of IO virt queues to use for blk device. Should > 0");
> > > > > > > > > > > > > > better:
> > > > > > > > > > > > > > 
> > > > > > > > > > > > > > +MODULE_PARM_DESC(num_io_request_queues,
> > > > > > > > > > > > > > +                "Limit number of IO request virt queues to use for each device. 0 for now limit");
> > > > > > > > > > > > > You proposed it and I replied on it bellow.
> > > > > > > > > > > > Can't say I understand 100% what you are saying. Want to send
> > > > > > > > > > > > a description that does make sense to you but
> > > > > > > > > > > > also reflects reality? 0 is the default so
> > > > > > > > > > > > "should > 0" besides being ungrammatical does not seem t"
> > > > > > > > > > > > reflect what it does ...
> > > > > > > > > > > if you "modprobe virtio_blk" the previous behavior will happen.
> > > > > > > > > > > 
> > > > > > > > > > > You can't "modprobe virtio_blk num_io_request_queues=0" since the minimal
> > > > > > > > > > > value is 1.
> > > > > > > > > > > 
> > > > > > > > > > > So your description is not reflecting the code.
> > > > > > > > > > > 
> > > > > > > > > > > We can do:
> > > > > > > > > > > 
> > > > > > > > > > > MODULE_PARM_DESC(num_io_request_queues, "Number of request virt queues to use for blk device. Minimum value is 1 queue");
> > > > > > > > > > What's the default value? We should document that.
> > > > > > > > > default value for static global variables is 0.
> > > > > > > > > 
> > > > > > > > > MODULE_PARM_DESC(num_io_request_queues, "Number of request virt queues to
> > > > > > > > > use for blk device. Minimum value is 1 queue. Default and Maximum value is
> > > > > > > > > equal to the total number of CPUs");
> > > > > > > > So it says it's the # of cpus but yoiu inspect it with
> > > > > > > > sysfs and it's actually 0. Let's say that's confusing
> > > > > > > > at the least. why not just let users set it to 0
> > > > > > > > and document that?
> > > > > > > > 
> > > > > > > Setting it by the user to 0 makes no sense.
> > > > > > > 
> > > > > > > We can say "if not set, the value equals to the total number of CPUs".
> > > > > > the value is 0. it seems to mean "no limit". the actual # of queues is
> > > > > > then te smaller between # of cpus and # of hardware queues.
> > > > > > I see no reason not to allow user to set that especially if
> > > > > > it was originally the value then user changed it
> > > > > > and is trying to change it back.
> > > > > I fine with that.
> > > > > 
> > > > > MODULE_PARM_DESC(num_io_request_queues, "Number of request virt queues to use for blk device. 0 value means no limitation");
> > > > > 
> > > > OK and the second distinction is that it's a limit on the
> > > > number, not the actual number. It's never more than what's provided
> > > > by the hypervisor.
> > > MODULE_PARM_DESC(num_io_request_queues, "Maximal number of request virt queues to use for blk device. 0 value means no limitation");
> > > 
> > > is that ok ?
> > 
> > Looks ok. And then do we need to limit this to nr_cpu_ids?
> > Setting a value that's too high seems harmless ...
> 
> why would you want that ?

So one can write a script that keeps working even when hypervisor
changes the # of CPU IDs.

It's also consistent with other parameters, e.g.:

        clocksource.verify_n_cpus= [KNL]
                        Limit the number of CPUs checked for clocksources
                        marked with CLOCK_SOURCE_VERIFY_PERCPU that
                        are marked unstable due to excessive skew.
                        A negative value says to check all CPUs, while
                        zero says not to check any.  Values larger than
                        nr_cpu_ids are silently truncated to nr_cpu_ids.

			^^^^^^^^^^^^

                        The actual CPUs are chosen randomly, with
                        no replacement if the same CPU is chosen twice.


> 
> > 
> > > > > > > The actual value of the created queues can be seen in /sys/block/vda/mq/ as
> > > > > > > done today.
> > > > > > > > > > > > > > > > > > +
> > > > > > > > > > > > > > > > > >          static int major;
> > > > > > > > > > > > > > > > > >          static DEFINE_IDA(vd_index_ida);
> > > > > > > > > > > > > > > > > > @@ -501,7 +517,9 @@ static int init_vq(struct virtio_blk *vblk)
> > > > > > > > > > > > > > > > > >          	if (err)
> > > > > > > > > > > > > > > > > >          		num_vqs = 1;
> > > > > > > > > > > > > > > > > > -	num_vqs = min_t(unsigned int, nr_cpu_ids, num_vqs);
> > > > > > > > > > > > > > > > > > +	num_vqs = min_t(unsigned int,
> > > > > > > > > > > > > > > > > > +			min_not_zero(num_io_queues, nr_cpu_ids),
> > > > > > > > > > > > > > > > > > +			num_vqs);
> > > > > > > > > > > > > > > > > If you respin, please consider calling them request queues. That's the
> > > > > > > > > > > > > > > > > terminology from the VIRTIO spec and it's nice to keep it consistent.
> > > > > > > > > > > > > > > > > But the purpose of num_io_queues is clear, so:
> > > > > > > > > > > > > > > > > 
> > > > > > > > > > > > > > > > > Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> > > > > > > > > > > > > > > > I did this:
> > > > > > > > > > > > > > > > +static unsigned int num_io_request_queues;
> > > > > > > > > > > > > > > > +module_param_cb(num_io_request_queues, &queue_count_ops, &num_io_request_queues, 0644);
> > > > > > > > > > > > > > > > +MODULE_PARM_DESC(num_io_request_queues,
> > > > > > > > > > > > > > > > +                "Limit number of IO request virt queues to use for each device. 0 for now limit");
> > > > > > > > > > > > > > > The parameter is writable and can be changed and then new devices might be
> > > > > > > > > > > > > > > probed with new value.
> > > > > > > > > > > > > > > 
> > > > > > > > > > > > > > > It can't be zero in the code. we can change param_set_uint_minmax args and
> > > > > > > > > > > > > > > say that 0 says nr_cpus.
> > > > > > > > > > > > > > > 
> > > > > > > > > > > > > > > I'm ok with the renaming but I prefer to stick to the description we gave in
> > > > > > > > > > > > > > > V3 of this patch (and maybe enable value of 0 as mentioned above).

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Re: [PATCH v2 1/1] virtio-blk: add num_io_queues module parameter

[Michael S. Tsirkin]

On Sun, Sep 12, 2021 at 01:33:13PM +0300, Max Gurtovoy wrote:
> 
> On 9/12/2021 12:50 PM, Michael S. Tsirkin wrote:
> > On Sun, Sep 12, 2021 at 12:37:26PM +0300, Max Gurtovoy wrote:
> > > On 9/12/2021 12:07 PM, Michael S. Tsirkin wrote:
> > > > On Sat, Sep 11, 2021 at 03:56:45PM +0300, Max Gurtovoy wrote:
> > > > > On 9/10/2021 1:57 AM, Michael S. Tsirkin wrote:
> > > > > > On Thu, Sep 09, 2021 at 07:45:42PM +0300, Max Gurtovoy wrote:
> > > > > > > On 9/9/2021 7:31 PM, Michael S. Tsirkin wrote:
> > > > > > > > On Thu, Sep 09, 2021 at 06:51:56PM +0300, Max Gurtovoy wrote:
> > > > > > > > > On 9/9/2021 6:40 PM, Michael S. Tsirkin wrote:
> > > > > > > > > > On Thu, Sep 09, 2021 at 06:37:37PM +0300, Max Gurtovoy wrote:
> > > > > > > > > > > On 9/9/2021 4:42 PM, Michael S. Tsirkin wrote:
> > > > > > > > > > > > On Mon, Sep 06, 2021 at 02:59:40PM +0300, Max Gurtovoy wrote:
> > > > > > > > > > > > > On 9/6/2021 2:20 PM, Michael S. Tsirkin wrote:
> > > > > > > > > > > > > > On Mon, Sep 06, 2021 at 01:31:32AM +0300, Max Gurtovoy wrote:
> > > > > > > > > > > > > > > On 9/5/2021 7:02 PM, Michael S. Tsirkin wrote:
> > > > > > > > > > > > > > > > On Thu, Sep 02, 2021 at 02:45:52PM +0100, Stefan Hajnoczi wrote:
> > > > > > > > > > > > > > > > > On Tue, Aug 31, 2021 at 04:50:35PM +0300, Max Gurtovoy wrote:
> > > > > > > > > > > > > > > > > > Sometimes a user would like to control the amount of IO queues to be
> > > > > > > > > > > > > > > > > > created for a block device. For example, for limiting the memory
> > > > > > > > > > > > > > > > > > footprint of virtio-blk devices.
> > > > > > > > > > > > > > > > > > 
> > > > > > > > > > > > > > > > > > Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
> > > > > > > > > > > > > > > > > > ---
> > > > > > > > > > > > > > > > > > 
> > > > > > > > > > > > > > > > > > changes from v1:
> > > > > > > > > > > > > > > > > >          - use param_set_uint_minmax (from Christoph)
> > > > > > > > > > > > > > > > > >          - added "Should > 0" to module description
> > > > > > > > > > > > > > > > > > 
> > > > > > > > > > > > > > > > > > Note: This commit apply on top of Jens's branch for-5.15/drivers
> > > > > > > > > > > > > > > > > > ---
> > > > > > > > > > > > > > > > > >          drivers/block/virtio_blk.c | 20 +++++++++++++++++++-
> > > > > > > > > > > > > > > > > >          1 file changed, 19 insertions(+), 1 deletion(-)
> > > > > > > > > > > > > > > > > > 
> > > > > > > > > > > > > > > > > > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> > > > > > > > > > > > > > > > > > index 4b49df2dfd23..9332fc4e9b31 100644
> > > > > > > > > > > > > > > > > > --- a/drivers/block/virtio_blk.c
> > > > > > > > > > > > > > > > > > +++ b/drivers/block/virtio_blk.c
> > > > > > > > > > > > > > > > > > @@ -24,6 +24,22 @@
> > > > > > > > > > > > > > > > > >          /* The maximum number of sg elements that fit into a virtqueue */
> > > > > > > > > > > > > > > > > >          #define VIRTIO_BLK_MAX_SG_ELEMS 32768
> > > > > > > > > > > > > > > > > > +static int virtblk_queue_count_set(const char *val,
> > > > > > > > > > > > > > > > > > +		const struct kernel_param *kp)
> > > > > > > > > > > > > > > > > > +{
> > > > > > > > > > > > > > > > > > +	return param_set_uint_minmax(val, kp, 1, nr_cpu_ids);
> > > > > > > > > > > > > > > > > > +}
> > > > > > > > > > > > > > Hmm which tree is this for?
> > > > > > > > > > > > > I've mentioned in the note that it apply on branch for-5.15/drivers. But now
> > > > > > > > > > > > > you can apply it on linus/master as well.
> > > > > > > > > > > > > 
> > > > > > > > > > > > > 
> > > > > > > > > > > > > > > > > > +
> > > > > > > > > > > > > > > > > > +static const struct kernel_param_ops queue_count_ops = {
> > > > > > > > > > > > > > > > > > +	.set = virtblk_queue_count_set,
> > > > > > > > > > > > > > > > > > +	.get = param_get_uint,
> > > > > > > > > > > > > > > > > > +};
> > > > > > > > > > > > > > > > > > +
> > > > > > > > > > > > > > > > > > +static unsigned int num_io_queues;
> > > > > > > > > > > > > > > > > > +module_param_cb(num_io_queues, &queue_count_ops, &num_io_queues, 0644);
> > > > > > > > > > > > > > > > > > +MODULE_PARM_DESC(num_io_queues,
> > > > > > > > > > > > > > > > > > +		 "Number of IO virt queues to use for blk device. Should > 0");
> > > > > > > > > > > > > > better:
> > > > > > > > > > > > > > 
> > > > > > > > > > > > > > +MODULE_PARM_DESC(num_io_request_queues,
> > > > > > > > > > > > > > +                "Limit number of IO request virt queues to use for each device. 0 for now limit");
> > > > > > > > > > > > > You proposed it and I replied on it bellow.
> > > > > > > > > > > > Can't say I understand 100% what you are saying. Want to send
> > > > > > > > > > > > a description that does make sense to you but
> > > > > > > > > > > > also reflects reality? 0 is the default so
> > > > > > > > > > > > "should > 0" besides being ungrammatical does not seem t"
> > > > > > > > > > > > reflect what it does ...
> > > > > > > > > > > if you "modprobe virtio_blk" the previous behavior will happen.
> > > > > > > > > > > 
> > > > > > > > > > > You can't "modprobe virtio_blk num_io_request_queues=0" since the minimal
> > > > > > > > > > > value is 1.
> > > > > > > > > > > 
> > > > > > > > > > > So your description is not reflecting the code.
> > > > > > > > > > > 
> > > > > > > > > > > We can do:
> > > > > > > > > > > 
> > > > > > > > > > > MODULE_PARM_DESC(num_io_request_queues, "Number of request virt queues to use for blk device. Minimum value is 1 queue");
> > > > > > > > > > What's the default value? We should document that.
> > > > > > > > > default value for static global variables is 0.
> > > > > > > > > 
> > > > > > > > > MODULE_PARM_DESC(num_io_request_queues, "Number of request virt queues to
> > > > > > > > > use for blk device. Minimum value is 1 queue. Default and Maximum value is
> > > > > > > > > equal to the total number of CPUs");
> > > > > > > > So it says it's the # of cpus but yoiu inspect it with
> > > > > > > > sysfs and it's actually 0. Let's say that's confusing
> > > > > > > > at the least. why not just let users set it to 0
> > > > > > > > and document that?
> > > > > > > > 
> > > > > > > Setting it by the user to 0 makes no sense.
> > > > > > > 
> > > > > > > We can say "if not set, the value equals to the total number of CPUs".
> > > > > > the value is 0. it seems to mean "no limit". the actual # of queues is
> > > > > > then te smaller between # of cpus and # of hardware queues.
> > > > > > I see no reason not to allow user to set that especially if
> > > > > > it was originally the value then user changed it
> > > > > > and is trying to change it back.
> > > > > I fine with that.
> > > > > 
> > > > > MODULE_PARM_DESC(num_io_request_queues, "Number of request virt queues to use for blk device. 0 value means no limitation");
> > > > > 
> > > > OK and the second distinction is that it's a limit on the
> > > > number, not the actual number. It's never more than what's provided
> > > > by the hypervisor.
> > > MODULE_PARM_DESC(num_io_request_queues, "Maximal number of request virt queues to use for blk device. 0 value means no limitation");
> > > 
> > > is that ok ?
> > 
> > Looks ok. And then do we need to limit this to nr_cpu_ids?
> > Setting a value that's too high seems harmless ...
> 
> why would you want that ?

So one can write a script that keeps working even when hypervisor
changes the # of CPU IDs.

It's also consistent with other parameters, e.g.:

        clocksource.verify_n_cpus= [KNL]
                        Limit the number of CPUs checked for clocksources
                        marked with CLOCK_SOURCE_VERIFY_PERCPU that
                        are marked unstable due to excessive skew.
                        A negative value says to check all CPUs, while
                        zero says not to check any.  Values larger than
                        nr_cpu_ids are silently truncated to nr_cpu_ids.

			^^^^^^^^^^^^

                        The actual CPUs are chosen randomly, with
                        no replacement if the same CPU is chosen twice.


> 
> > 
> > > > > > > The actual value of the created queues can be seen in /sys/block/vda/mq/ as
> > > > > > > done today.
> > > > > > > > > > > > > > > > > > +
> > > > > > > > > > > > > > > > > >          static int major;
> > > > > > > > > > > > > > > > > >          static DEFINE_IDA(vd_index_ida);
> > > > > > > > > > > > > > > > > > @@ -501,7 +517,9 @@ static int init_vq(struct virtio_blk *vblk)
> > > > > > > > > > > > > > > > > >          	if (err)
> > > > > > > > > > > > > > > > > >          		num_vqs = 1;
> > > > > > > > > > > > > > > > > > -	num_vqs = min_t(unsigned int, nr_cpu_ids, num_vqs);
> > > > > > > > > > > > > > > > > > +	num_vqs = min_t(unsigned int,
> > > > > > > > > > > > > > > > > > +			min_not_zero(num_io_queues, nr_cpu_ids),
> > > > > > > > > > > > > > > > > > +			num_vqs);
> > > > > > > > > > > > > > > > > If you respin, please consider calling them request queues. That's the
> > > > > > > > > > > > > > > > > terminology from the VIRTIO spec and it's nice to keep it consistent.
> > > > > > > > > > > > > > > > > But the purpose of num_io_queues is clear, so:
> > > > > > > > > > > > > > > > > 
> > > > > > > > > > > > > > > > > Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> > > > > > > > > > > > > > > > I did this:
> > > > > > > > > > > > > > > > +static unsigned int num_io_request_queues;
> > > > > > > > > > > > > > > > +module_param_cb(num_io_request_queues, &queue_count_ops, &num_io_request_queues, 0644);
> > > > > > > > > > > > > > > > +MODULE_PARM_DESC(num_io_request_queues,
> > > > > > > > > > > > > > > > +                "Limit number of IO request virt queues to use for each device. 0 for now limit");
> > > > > > > > > > > > > > > The parameter is writable and can be changed and then new devices might be
> > > > > > > > > > > > > > > probed with new value.
> > > > > > > > > > > > > > > 
> > > > > > > > > > > > > > > It can't be zero in the code. we can change param_set_uint_minmax args and
> > > > > > > > > > > > > > > say that 0 says nr_cpus.
> > > > > > > > > > > > > > > 
> > > > > > > > > > > > > > > I'm ok with the renaming but I prefer to stick to the description we gave in
> > > > > > > > > > > > > > > V3 of this patch (and maybe enable value of 0 as mentioned above).

Re: [PATCH v2 1/1] virtio-blk: add num_io_queues module parameter

[Max Gurtovoy]

On 9/12/2021 2:45 PM, Michael S. Tsirkin wrote:
> On Sun, Sep 12, 2021 at 01:33:13PM +0300, Max Gurtovoy wrote:
>> On 9/12/2021 12:50 PM, Michael S. Tsirkin wrote:
>>> On Sun, Sep 12, 2021 at 12:37:26PM +0300, Max Gurtovoy wrote:
>>>> On 9/12/2021 12:07 PM, Michael S. Tsirkin wrote:
>>>>> On Sat, Sep 11, 2021 at 03:56:45PM +0300, Max Gurtovoy wrote:
>>>>>> On 9/10/2021 1:57 AM, Michael S. Tsirkin wrote:
>>>>>>> On Thu, Sep 09, 2021 at 07:45:42PM +0300, Max Gurtovoy wrote:
>>>>>>>> On 9/9/2021 7:31 PM, Michael S. Tsirkin wrote:
>>>>>>>>> On Thu, Sep 09, 2021 at 06:51:56PM +0300, Max Gurtovoy wrote:
>>>>>>>>>> On 9/9/2021 6:40 PM, Michael S. Tsirkin wrote:
>>>>>>>>>>> On Thu, Sep 09, 2021 at 06:37:37PM +0300, Max Gurtovoy wrote:
>>>>>>>>>>>> On 9/9/2021 4:42 PM, Michael S. Tsirkin wrote:
>>>>>>>>>>>>> On Mon, Sep 06, 2021 at 02:59:40PM +0300, Max Gurtovoy wrote:
>>>>>>>>>>>>>> On 9/6/2021 2:20 PM, Michael S. Tsirkin wrote:
>>>>>>>>>>>>>>> On Mon, Sep 06, 2021 at 01:31:32AM +0300, Max Gurtovoy wrote:
>>>>>>>>>>>>>>>> On 9/5/2021 7:02 PM, Michael S. Tsirkin wrote:
>>>>>>>>>>>>>>>>> On Thu, Sep 02, 2021 at 02:45:52PM +0100, Stefan Hajnoczi wrote:
>>>>>>>>>>>>>>>>>> On Tue, Aug 31, 2021 at 04:50:35PM +0300, Max Gurtovoy wrote:
>>>>>>>>>>>>>>>>>>> Sometimes a user would like to control the amount of IO queues to be
>>>>>>>>>>>>>>>>>>> created for a block device. For example, for limiting the memory
>>>>>>>>>>>>>>>>>>> footprint of virtio-blk devices.
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>> Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
>>>>>>>>>>>>>>>>>>> ---
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>> changes from v1:
>>>>>>>>>>>>>>>>>>>           - use param_set_uint_minmax (from Christoph)
>>>>>>>>>>>>>>>>>>>           - added "Should > 0" to module description
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>> Note: This commit apply on top of Jens's branch for-5.15/drivers
>>>>>>>>>>>>>>>>>>> ---
>>>>>>>>>>>>>>>>>>>           drivers/block/virtio_blk.c | 20 +++++++++++++++++++-
>>>>>>>>>>>>>>>>>>>           1 file changed, 19 insertions(+), 1 deletion(-)
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
>>>>>>>>>>>>>>>>>>> index 4b49df2dfd23..9332fc4e9b31 100644
>>>>>>>>>>>>>>>>>>> --- a/drivers/block/virtio_blk.c
>>>>>>>>>>>>>>>>>>> +++ b/drivers/block/virtio_blk.c
>>>>>>>>>>>>>>>>>>> @@ -24,6 +24,22 @@
>>>>>>>>>>>>>>>>>>>           /* The maximum number of sg elements that fit into a virtqueue */
>>>>>>>>>>>>>>>>>>>           #define VIRTIO_BLK_MAX_SG_ELEMS 32768
>>>>>>>>>>>>>>>>>>> +static int virtblk_queue_count_set(const char *val,
>>>>>>>>>>>>>>>>>>> +		const struct kernel_param *kp)
>>>>>>>>>>>>>>>>>>> +{
>>>>>>>>>>>>>>>>>>> +	return param_set_uint_minmax(val, kp, 1, nr_cpu_ids);
>>>>>>>>>>>>>>>>>>> +}
>>>>>>>>>>>>>>> Hmm which tree is this for?
>>>>>>>>>>>>>> I've mentioned in the note that it apply on branch for-5.15/drivers. But now
>>>>>>>>>>>>>> you can apply it on linus/master as well.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>>>>> +static const struct kernel_param_ops queue_count_ops = {
>>>>>>>>>>>>>>>>>>> +	.set = virtblk_queue_count_set,
>>>>>>>>>>>>>>>>>>> +	.get = param_get_uint,
>>>>>>>>>>>>>>>>>>> +};
>>>>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>>>>> +static unsigned int num_io_queues;
>>>>>>>>>>>>>>>>>>> +module_param_cb(num_io_queues, &queue_count_ops, &num_io_queues, 0644);
>>>>>>>>>>>>>>>>>>> +MODULE_PARM_DESC(num_io_queues,
>>>>>>>>>>>>>>>>>>> +		 "Number of IO virt queues to use for blk device. Should > 0");
>>>>>>>>>>>>>>> better:
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> +MODULE_PARM_DESC(num_io_request_queues,
>>>>>>>>>>>>>>> +                "Limit number of IO request virt queues to use for each device. 0 for now limit");
>>>>>>>>>>>>>> You proposed it and I replied on it bellow.
>>>>>>>>>>>>> Can't say I understand 100% what you are saying. Want to send
>>>>>>>>>>>>> a description that does make sense to you but
>>>>>>>>>>>>> also reflects reality? 0 is the default so
>>>>>>>>>>>>> "should > 0" besides being ungrammatical does not seem t"
>>>>>>>>>>>>> reflect what it does ...
>>>>>>>>>>>> if you "modprobe virtio_blk" the previous behavior will happen.
>>>>>>>>>>>>
>>>>>>>>>>>> You can't "modprobe virtio_blk num_io_request_queues=0" since the minimal
>>>>>>>>>>>> value is 1.
>>>>>>>>>>>>
>>>>>>>>>>>> So your description is not reflecting the code.
>>>>>>>>>>>>
>>>>>>>>>>>> We can do:
>>>>>>>>>>>>
>>>>>>>>>>>> MODULE_PARM_DESC(num_io_request_queues, "Number of request virt queues to use for blk device. Minimum value is 1 queue");
>>>>>>>>>>> What's the default value? We should document that.
>>>>>>>>>> default value for static global variables is 0.
>>>>>>>>>>
>>>>>>>>>> MODULE_PARM_DESC(num_io_request_queues, "Number of request virt queues to
>>>>>>>>>> use for blk device. Minimum value is 1 queue. Default and Maximum value is
>>>>>>>>>> equal to the total number of CPUs");
>>>>>>>>> So it says it's the # of cpus but yoiu inspect it with
>>>>>>>>> sysfs and it's actually 0. Let's say that's confusing
>>>>>>>>> at the least. why not just let users set it to 0
>>>>>>>>> and document that?
>>>>>>>>>
>>>>>>>> Setting it by the user to 0 makes no sense.
>>>>>>>>
>>>>>>>> We can say "if not set, the value equals to the total number of CPUs".
>>>>>>> the value is 0. it seems to mean "no limit". the actual # of queues is
>>>>>>> then te smaller between # of cpus and # of hardware queues.
>>>>>>> I see no reason not to allow user to set that especially if
>>>>>>> it was originally the value then user changed it
>>>>>>> and is trying to change it back.
>>>>>> I fine with that.
>>>>>>
>>>>>> MODULE_PARM_DESC(num_io_request_queues, "Number of request virt queues to use for blk device. 0 value means no limitation");
>>>>>>
>>>>> OK and the second distinction is that it's a limit on the
>>>>> number, not the actual number. It's never more than what's provided
>>>>> by the hypervisor.
>>>> MODULE_PARM_DESC(num_io_request_queues, "Maximal number of request virt queues to use for blk device. 0 value means no limitation");
>>>>
>>>> is that ok ?
>>> Looks ok. And then do we need to limit this to nr_cpu_ids?
>>> Setting a value that's too high seems harmless ...
>> why would you want that ?
> So one can write a script that keeps working even when hypervisor
> changes the # of CPU IDs.
>
> It's also consistent with other parameters, e.g.:
>
>          clocksource.verify_n_cpus= [KNL]
>                          Limit the number of CPUs checked for clocksources
>                          marked with CLOCK_SOURCE_VERIFY_PERCPU that
>                          are marked unstable due to excessive skew.
>                          A negative value says to check all CPUs, while
>                          zero says not to check any.  Values larger than
>                          nr_cpu_ids are silently truncated to nr_cpu_ids.
>
> 			^^^^^^^^^^^^
>
>                          The actual CPUs are chosen randomly, with
>                          no replacement if the same CPU is chosen twice.

I don't understand how this example is relevant. It's not a blk-mq 
device that allocate queues for submitting IOs.

There is no sense of creating more queues than the #CPUs in the blk-mq 
design.

And also no reason setting it to some high value that we'll silently 
decrease.

Why would anyone write a script with hard coded values of CPUs instead 
of checking it with some linux tool and then set the module param 
accordingly ?


>
>>>>>>>> The actual value of the created queues can be seen in /sys/block/vda/mq/ as
>>>>>>>> done today.
>>>>>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>>>>>>           static int major;
>>>>>>>>>>>>>>>>>>>           static DEFINE_IDA(vd_index_ida);
>>>>>>>>>>>>>>>>>>> @@ -501,7 +517,9 @@ static int init_vq(struct virtio_blk *vblk)
>>>>>>>>>>>>>>>>>>>           	if (err)
>>>>>>>>>>>>>>>>>>>           		num_vqs = 1;
>>>>>>>>>>>>>>>>>>> -	num_vqs = min_t(unsigned int, nr_cpu_ids, num_vqs);
>>>>>>>>>>>>>>>>>>> +	num_vqs = min_t(unsigned int,
>>>>>>>>>>>>>>>>>>> +			min_not_zero(num_io_queues, nr_cpu_ids),
>>>>>>>>>>>>>>>>>>> +			num_vqs);
>>>>>>>>>>>>>>>>>> If you respin, please consider calling them request queues. That's the
>>>>>>>>>>>>>>>>>> terminology from the VIRTIO spec and it's nice to keep it consistent.
>>>>>>>>>>>>>>>>>> But the purpose of num_io_queues is clear, so:
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
>>>>>>>>>>>>>>>>> I did this:
>>>>>>>>>>>>>>>>> +static unsigned int num_io_request_queues;
>>>>>>>>>>>>>>>>> +module_param_cb(num_io_request_queues, &queue_count_ops, &num_io_request_queues, 0644);
>>>>>>>>>>>>>>>>> +MODULE_PARM_DESC(num_io_request_queues,
>>>>>>>>>>>>>>>>> +                "Limit number of IO request virt queues to use for each device. 0 for now limit");
>>>>>>>>>>>>>>>> The parameter is writable and can be changed and then new devices might be
>>>>>>>>>>>>>>>> probed with new value.
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> It can't be zero in the code. we can change param_set_uint_minmax args and
>>>>>>>>>>>>>>>> say that 0 says nr_cpus.
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> I'm ok with the renaming but I prefer to stick to the description we gave in
>>>>>>>>>>>>>>>> V3 of this patch (and maybe enable value of 0 as mentioned above).