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

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Date:	Wed, 4 Dec 2013 01:24:00 -0800 (PST)
From:	Joseph Gasparakis <joseph.gasparakis@...el.com>
To:	Or Gerlitz <or.gerlitz@...il.com>
cc:	Joseph Gasparakis <joseph.gasparakis@...el.com>,
	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, 4 Dec 2013, Or Gerlitz wrote:

> 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.
> 

Ok, I was really hoping that would be the same... And just for the record, 
you are seeing (SKB_UDP_TUNNEL | SKB_GSO_TCPV4) as 0x201 while I was 
seeing it as 0x81 because commit 61c1db7fae "ipv6: sit: add GSO/TSO 
support" pushed the SKB_UDP_TUNNEL two bits left, and I had done my tests 
before it.
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