Re: [PATCH net-next] net: enable RPS on vlan devices

[Eric Dumazet <eric.dumazet@gmail.com>]

On 10/09/2018 05:41 PM, Shannon Nelson wrote:
> From: Silviu Smarandache <silviu.smarandache@oracle.com>
> 
> This patch modifies the RPS processing code so that it searches
> for a matching vlan interface on the packet and then uses the
> RPS settings of the vlan interface.  If no vlan interface
> is found or the vlan interface does not have RPS enabled,
> it will fall back to the RPS settings of the underlying device.
> 
> In supporting VMs where we can't control the OS being used,
> we'd like to separate the VM cpu processing from the host's
> cpus as a way to help mitigate the impact of the L1TF issue.
> When running the VM's traffic on a vlan we can stick the Rx
> processing on one set of cpus separate from the VM's cpus.
> Yes, choosing to use this may cause a bit of throughput pain
> when the packets are actually passed into the VM and have to
> move from one cache to another.
> 
> Orabug: 28645929
> 
> Signed-off-by: Silviu Smarandache <silviu.smarandache@oracle.com>
> Signed-off-by: Shannon Nelson <shannon.nelson@oracle.com>
> ---
>  net/core/dev.c | 59 +++++++++++++++++++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 56 insertions(+), 3 deletions(-)
> 
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 0b2d777..1da3f63 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -3971,8 +3971,8 @@ set_rps_cpu(struct net_device *dev, struct sk_buff *skb,
>   * CPU from the RPS map of the receiving queue for a given skb.
>   * rcu_read_lock must be held on entry.
>   */
> -static int get_rps_cpu(struct net_device *dev, struct sk_buff *skb,
> -		       struct rps_dev_flow **rflowp)
> +static int __get_rps_cpu(struct net_device *dev, struct sk_buff *skb,
> +			 struct rps_dev_flow **rflowp)
>  {
>  	const struct rps_sock_flow_table *sock_flow_table;
>  	struct netdev_rx_queue *rxqueue = dev->_rx;
> @@ -4066,6 +4066,35 @@ static int get_rps_cpu(struct net_device *dev, struct sk_buff *skb,
>  	return cpu;
>  }
>  
> +static int get_rps_cpu(struct net_device *dev, struct sk_buff *skb,
> +		       struct rps_dev_flow **rflowp)
> +{
> +	/* Check for a vlan device with RPS settings */
> +	if (skb_vlan_tag_present(skb)) {
> +		struct net_device *vdev;
> +		u16 vid;
> +
> +		vid = skb_vlan_tag_get_id(skb);
> +		vdev = __vlan_find_dev_deep_rcu(dev, skb->vlan_proto, vid);
> +		if (vdev) {
> +			/* recorded queue is not referring to the vlan device.
> +			 * Save and restore it
> +			 */
> +			int cpu;
> +			u16 queue_mapping = skb_get_queue_mapping(skb);
> +
> +			skb_set_queue_mapping(skb, 0);
> +			cpu = __get_rps_cpu(vdev, skb, rflowp);
> +			skb_set_queue_mapping(skb, queue_mapping);

This is really ugly :/

Also what makes vlan so special compared to say macvlan ?