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

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

[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

[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

[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 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

[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

[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

[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

[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

[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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