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

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Date:	Wed, 4 Dec 2013 10:35:18 +0200
From:	Or Gerlitz <or.gerlitz@...il.com>
To:	Joseph Gasparakis <joseph.gasparakis@...el.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Jerry Chu <hkchu@...gle.com>,
	Or Gerlitz <ogerlitz@...lanox.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Alexei Starovoitov <ast@...mgrid.com>,
	Pravin B Shelar <pshelar@...ira.com>,
	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>
Subject: Re: vxlan/veth performance issues on net.git + latest kernels

On Wed, Dec 4, 2013 at 2:35 AM, Joseph Gasparakis
<joseph.gasparakis@...el.com> wrote:

> I was printing the gso_type in vxlan_xmit_skb(), right before
> iptunnel_xmit() gets called (I was focus UDPv4 encap only). Then I saw the
> gso_type was different when a VM was involved and when it was not
> (although I was transmitting exactly the same packet), and then I replaced
> my printk with something like skb_shinfo(skb)->gso_type = <the gso type I had
> for non-VM skb> and it all worked.
>
> Then I looked into what was different between the two gso_types and the
> only difference was that SKB_GSO_DODGY was set when Tx'ing from the VM.
> I am sure I could have been more delicate with the aproach, but hey, it
> worked for me.
>
> I would be curious to see if this is the same issue as mine. It seems like it is.

nope! with the latest net tree, after handle_offloads is called in
vxlan_xmit_skb and before iptunnel_xmit is invoked,
skb_shinfo(skb)->gso_type is either 0 or 0x201 which is
(SKB_GSO_UDP_TUNNEL | SKB_GSO_TCPV4) and its the same value whether
the session runs over veth device or directly over the bridge, where
over veth and > 1 stream we see drops, bad perf, etc.

I am very interested in the VM case too, so will check it out and let you know.
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