netdev - Re: [PATCH net-next] vxlan: distribute vxlan tunneled traffic across multiple TXQs

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Date:	Mon, 23 Dec 2013 11:28:54 -0800
From:	Stephen Hemminger <stephen@...workplumber.org>
To:	Sathya Perla <sathya.perla@...lex.com>
Cc:	<netdev@...r.kernel.org>, <edumazet@...gle.com>
Subject: Re: [PATCH net-next] vxlan: distribute vxlan tunneled traffic
 across multiple TXQs

On Mon, 23 Dec 2013 18:26:53 +0530
Sathya Perla <sathya.perla@...lex.com> wrote:

> The vxlan driver sets itself as the socket owner for all the TX flows
> it encapsulates (using vxlan_set_owner()) and assigns it's own skb
> destructor. This causes all tunneled traffic to land up on only one TXQ
> as all encapsulated skbs refer to the vxlan socket and not the original
> socket.  Also, the vxlan skb destructor breaks some functionality for
> tunneled traffic like wmem accounting and as Eric D. mentioned, TCP
> small queues and FQ/pacing packet scheduler too.
> 
> This patch removes vxlan ownership on tunneled skbs. This causes
> tunneled traffic to be hashed into multiple TXQs based on the original
> socket hash.
> 
> Signed-off-by: Sathya Perla <sathya.perla@...lex.com>
> ---
>  drivers/net/vxlan.c |   22 +++-------------------
>  1 files changed, 3 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/net/vxlan.c b/drivers/net/vxlan.c
> index aef44aa..eb55c08 100644
> --- a/drivers/net/vxlan.c
> +++ b/drivers/net/vxlan.c
> @@ -1381,20 +1381,6 @@ static bool route_shortcircuit(struct net_device *dev, struct sk_buff *skb)
>  	return false;
>  }
>  
> -static void vxlan_sock_put(struct sk_buff *skb)
> -{
> -	sock_put(skb->sk);
> -}
> -
> -/* On transmit, associate with the tunnel socket */
> -static void vxlan_set_owner(struct sock *sk, struct sk_buff *skb)
> -{
> -	skb_orphan(skb);
> -	sock_hold(sk);
> -	skb->sk = sk;
> -	skb->destructor = vxlan_sock_put;
> -}
> -
>  /* Compute source port for outgoing packet
>   *   first choice to use L4 flow hash since it will spread
>   *     better and maybe available from hardware
> @@ -1514,8 +1500,6 @@ static int vxlan6_xmit_skb(struct vxlan_sock *vs,
>  	ip6h->daddr	  = *daddr;
>  	ip6h->saddr	  = *saddr;
>  
> -	vxlan_set_owner(vs->sock->sk, skb);
> -
>  	err = handle_offloads(skb);
>  	if (err)
>  		return err;
> @@ -1572,8 +1556,6 @@ int vxlan_xmit_skb(struct vxlan_sock *vs,
>  	uh->len = htons(skb->len);
>  	uh->check = 0;
>  
> -	vxlan_set_owner(vs->sock->sk, skb);
> -
>  	err = handle_offloads(skb);
>  	if (err)
>  		return err;
> @@ -1836,8 +1818,10 @@ static netdev_tx_t vxlan_xmit(struct sk_buff *skb, struct net_device *dev)
>  		struct sk_buff *skb1;
>  
>  		skb1 = skb_clone(skb, GFP_ATOMIC);
> -		if (skb1)
> +		if (skb1) {
> +			skb1->sk = skb->sk;
>  			vxlan_xmit_one(skb1, dev, rdst, did_rsc);
> +		}
>  	}
>  
>  	dev_kfree_skb(skb);

The idea is good, but without the destructor there is nothing to keep
the UDP socket from being destroyed while packet is being sent on another
CPU.
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