netdev - Re: vxlan/veth performance issues on net.git + latest kernels

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Date:	Tue, 3 Dec 2013 16:26:28 -0800
From:	Alexei Starovoitov <ast@...mgrid.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Or Gerlitz <or.gerlitz@...il.com>,
	David Miller <davem@...emloft.net>,
	Joseph Gasparakis <joseph.gasparakis@...el.com>,
	Jerry Chu <hkchu@...gle.com>,
	Or Gerlitz <ogerlitz@...lanox.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Pravin B Shelar <pshelar@...ira.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: vxlan/veth performance issues on net.git + latest kernels

On Tue, Dec 3, 2013 at 3:59 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
>
> +#define SKB_CONSUMED_MAGIC ((void *)0xDEAD0001)
> +static inline void dev_consume_skb_any(struct sk_buff *skb)
> +{
> +       skb->dev = SKB_CONSUMED_MAGIC;
> +       dev_kfree_skb_any(skb);
> +}
> +
>  int netif_rx(struct sk_buff *skb);
>  int netif_rx_ni(struct sk_buff *skb);
>  int netif_receive_skb(struct sk_buff *skb);
> diff --git a/net/core/dev.c b/net/core/dev.c
> index ba3b7ea5ebb3..b2b0e5776ce9 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -3306,7 +3306,10 @@ static void net_tx_action(struct softirq_action *h)
>                         clist = clist->next;
>
>                         WARN_ON(atomic_read(&skb->users));
> -                       trace_kfree_skb(skb, net_tx_action);
> +                       if (likely(skb->dev == SKB_CONSUMED_MAGIC))
> +                               trace_consume_skb(skb);
> +                       else
> +                               trace_kfree_skb(skb, net_tx_action);

Could you use some other way to mark skb ?
In tracing we might want to examine skb more carefully and not being
able to see the device
will limit the usability of this tracepoint.
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