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

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Date:	Tue, 3 Dec 2013 16:34:35 -0800
From:	Alexei Starovoitov <ast@...mgrid.com>
To:	Joseph Gasparakis <joseph.gasparakis@...el.com>
Cc:	Or Gerlitz <or.gerlitz@...il.com>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Jerry Chu <hkchu@...gle.com>,
	Or Gerlitz <ogerlitz@...lanox.com>,
	Eric Dumazet <edumazet@...gle.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 Tue, Dec 3, 2013 at 4:35 PM, 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.

hmm. dodgy should be a normal path from vm.
kvm suppose to negotiate vnet_hdr for tap/macvtap and corresponding
driver will be remapping virtio_net_gso* flags into skb_gso_* flags
plus gso_dodgy.
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