Re: [PATCH 1/2] vdpa: Allow to configure max data virtqueues

[Si-Wei Liu <si-wei.liu@oracle.com>]

On 11/30/2021 1:48 AM, Eli Cohen wrote:
> Allow to configure the max virtqueues for a device.
>
> Signed-off-by: Eli Cohen <elic@nvidia.com>
> ---
>   drivers/vdpa/vdpa.c  | 16 +++++++++++++++-
>   include/linux/vdpa.h |  1 +
>   2 files changed, 16 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/vdpa/vdpa.c b/drivers/vdpa/vdpa.c
> index 7332a74a4b00..e185ec2ee851 100644
> --- a/drivers/vdpa/vdpa.c
> +++ b/drivers/vdpa/vdpa.c
> @@ -480,7 +480,8 @@ vdpa_nl_cmd_mgmtdev_get_dumpit(struct sk_buff *msg, struct netlink_callback *cb)
>   }
>   
>   #define VDPA_DEV_NET_ATTRS_MASK ((1 << VDPA_ATTR_DEV_NET_CFG_MACADDR) | \
> -				 (1 << VDPA_ATTR_DEV_NET_CFG_MTU))
> +				 (1 << VDPA_ATTR_DEV_NET_CFG_MTU) | \
> +				 (1 << VDPA_ATTR_DEV_NET_CFG_MAX_VQP))
It seems VDPA_ATTR_DEV_MAX_VQS (u32) is what you want (# of data 
virtqueues instead of # of data virtqueue pairs)? Not sure what's 
possible use of VDPA_ATTR_DEV_NET_CFG_MAX_VQP, was it to dump/display 
the config space max_virtqueue_pairs value (u16, 1-32768) for 
virtio-net? Why there's such quasi-duplicate attribute introduced in the 
first place?

Not even sure VDPA_ATTR_DEV_MAX_VQS by definition should include other 
virtqueues as well: such as control virtqueue or event virtqueue. Hence 
the name will be more applicable to vdpa devices of other virtio type 
than just virtio-net. Otherwise I would think this attribute is slightly 
misnamed (max_data_vqs might be a proper name).

>   
>   static int vdpa_nl_cmd_dev_add_set_doit(struct sk_buff *skb, struct genl_info *info)
>   {
> @@ -506,6 +507,19 @@ static int vdpa_nl_cmd_dev_add_set_doit(struct sk_buff *skb, struct genl_info *i
>   			nla_get_u16(nl_attrs[VDPA_ATTR_DEV_NET_CFG_MTU]);
>   		config.mask |= (1 << VDPA_ATTR_DEV_NET_CFG_MTU);
>   	}
> +	if (nl_attrs[VDPA_ATTR_DEV_NET_CFG_MAX_VQP]) {
> +		config.max_virtqueues = nla_get_u16(nl_attrs[VDPA_ATTR_DEV_NET_CFG_MAX_VQP]);
> +		if (config.max_virtqueues < 2) {
> +			NL_SET_ERR_MSG_MOD(info->extack, "At least two virtqueues are required");
> +			return -EINVAL;
> +		}
> +		if ((config.max_virtqueues - 1) & config.max_virtqueues) {
> +			NL_SET_ERR_MSG_MOD(info->extack,
> +					   "Must provide power of two number of virtqueues");
Why there's such limitation for the number of vDPA virtqueues? I thought 
the software virtio doesn't have this limitation (power of two).

-Siwei

> +			return -EINVAL;
> +		}
> +		config.mask |= BIT_ULL(VDPA_ATTR_DEV_NET_CFG_MAX_VQP);
> +	}
>   
>   	/* Skip checking capability if user didn't prefer to configure any
>   	 * device networking attributes. It is likely that user might have used
> diff --git a/include/linux/vdpa.h b/include/linux/vdpa.h
> index c3011ccda430..2f0b09c6d1ae 100644
> --- a/include/linux/vdpa.h
> +++ b/include/linux/vdpa.h
> @@ -101,6 +101,7 @@ struct vdpa_dev_set_config {
>   		u16 mtu;
>   	} net;
>   	u64 mask;
> +	u16 max_virtqueues;
>   };
>   
>   /**

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