Linux Virtualization - Jan 2018 - [RFC PATCH net-next v2 2/2] virtio_net: Extend virtio to use VF datapath when available

On 2018?01?12? 13:58, Sridhar Samudrala wrote:
>   static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device
*dev)
>   {
>   	struct virtnet_info *vi = netdev_priv(dev);
>   	int qnum = skb_get_queue_mapping(skb);
>   	struct send_queue *sq = &vi->sq[qnum];
> +	struct net_device *vf_netdev;
>   	int err;
>   	struct netdev_queue *txq = netdev_get_tx_queue(dev, qnum);
>   	bool kick = !skb->xmit_more;
>   	bool use_napi = sq->napi.weight;
>   
> +	/* If VF is present and up then redirect packets
> +	 * called with rcu_read_lock_bh
> +	 */
> +	vf_netdev = rcu_dereference_bh(vi->vf_netdev);
> +	if (vf_netdev && netif_running(vf_netdev) &&
> +	    !netpoll_tx_running(dev) &&
> +	    is_unicast_ether_addr(eth_hdr(skb)->h_dest))
> +		return virtnet_vf_xmit(dev, vf_netdev, skb);
> +
A question here.

If I read the code correctly, all features were validated against virtio 
instead VF before transmitting. This assumes VF's feature is a superset 
of virtio, does this really work? Do we need to sanitize the feature 
before joining? (e.g at last NETIF_R_GSO_ROBUST needs to be removed).

Thanks

On 1/23/2018 2:33 AM, Jason Wang wrote:
>
>
> On 2018?01?12? 13:58, Sridhar Samudrala wrote:
>> ? static netdev_tx_t start_xmit(struct sk_buff *skb, struct 
>> net_device *dev)
>> ? {
>> ????? struct virtnet_info *vi = netdev_priv(dev);
>> ????? int qnum = skb_get_queue_mapping(skb);
>> ????? struct send_queue *sq = &vi->sq[qnum];
>> +??? struct net_device *vf_netdev;
>> ????? int err;
>> ????? struct netdev_queue *txq = netdev_get_tx_queue(dev, qnum);
>> ????? bool kick = !skb->xmit_more;
>> ????? bool use_napi = sq->napi.weight;
>> ? +??? /* If VF is present and up then redirect packets
>> +???? * called with rcu_read_lock_bh
>> +???? */
>> +??? vf_netdev = rcu_dereference_bh(vi->vf_netdev);
>> +??? if (vf_netdev && netif_running(vf_netdev) &&
>> +??????? !netpoll_tx_running(dev) &&
>> +??????? is_unicast_ether_addr(eth_hdr(skb)->h_dest))
>> +??????? return virtnet_vf_xmit(dev, vf_netdev, skb);
>> +
>
> A question here.
>
> If I read the code correctly, all features were validated against 
> virtio instead VF before transmitting. This assumes VF's feature is a 
> superset of virtio, does this really work? Do we need to sanitize the 
> feature before joining? (e.g at last NETIF_R_GSO_ROBUST needs to be 
> removed).
Actually, virtnet_vf_xmit() calls dev_queue_xmit() after updating 
skb->dev to vf netdev.
So the features get validated against VF features and the right tx queue 
is selected
before the real transmit.

Thanks
Sridhar

On 2018?01?24? 00:03, Samudrala, Sridhar wrote:
>
>
> On 1/23/2018 2:33 AM, Jason Wang wrote:
>>
>>
>> On 2018?01?12? 13:58, Sridhar Samudrala wrote:
>>> ? static netdev_tx_t start_xmit(struct sk_buff *skb, struct 
>>> net_device *dev)
>>> ? {
>>> ????? struct virtnet_info *vi = netdev_priv(dev);
>>> ????? int qnum = skb_get_queue_mapping(skb);
>>> ????? struct send_queue *sq = &vi->sq[qnum];
>>> +??? struct net_device *vf_netdev;
>>> ????? int err;
>>> ????? struct netdev_queue *txq = netdev_get_tx_queue(dev, qnum);
>>> ????? bool kick = !skb->xmit_more;
>>> ????? bool use_napi = sq->napi.weight;
>>> ? +??? /* If VF is present and up then redirect packets
>>> +???? * called with rcu_read_lock_bh
>>> +???? */
>>> +??? vf_netdev = rcu_dereference_bh(vi->vf_netdev);
>>> +??? if (vf_netdev && netif_running(vf_netdev) &&
>>> +??????? !netpoll_tx_running(dev) &&
>>> +??????? is_unicast_ether_addr(eth_hdr(skb)->h_dest))
>>> +??????? return virtnet_vf_xmit(dev, vf_netdev, skb);
>>> +
>>
>> A question here.
>>
>> If I read the code correctly, all features were validated against 
>> virtio instead VF before transmitting. This assumes VF's feature is
a
>> superset of virtio, does this really work? Do we need to sanitize the 
>> feature before joining? (e.g at last NETIF_R_GSO_ROBUST needs to be 
>> removed).
>
> Actually, virtnet_vf_xmit() calls dev_queue_xmit() after updating 
> skb->dev to vf netdev.
> So the features get validated against VF features and the right tx 
> queue is selected
> before the real transmit.
I see, the the packet will go through qdiscs twice which is suboptimal. 
And the device may lose some ability of VF like tunnel GSO.

Thanks
>
> Thanks
> Sridhar
>
>
>