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

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Date:	Tue, 3 Dec 2013 17:29:06 -0800 (PST)
From:	Joseph Gasparakis <joseph.gasparakis@...el.com>
To:	Alexei Starovoitov <ast@...mgrid.com>
cc:	Joseph Gasparakis <joseph.gasparakis@...el.com>,
	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, 3 Dec 2013, Alexei Starovoitov wrote:

> 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.
> 

Then would the fix be as simple as just unsetting the bit in vxlan? 
Because I am guessing that there is a bug somewhere where the combination of 
GSO_UDP_TUNNEL and GSO_DODGY. That would solve my problem, hopefully Or's 
too if it is the same.
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