Re: [Xen-users] Xen/OVS - VLAN offloading

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Fri, 2013-05-31 at 11:18 +0300, Eugene Istomin wrote:
> Ian,
> 
> in my testbed untagged by OVS have ~2 times more bandwith than untagged by VM.
> 
> All interfaces have MTU=9000
> 
> 
> 1)untagged by VM interface (in OVS like "trunks: [1002]")
> 
> #atop from VM
> NET | transport    | tcpi   22733 | tcpo   80191 | udpi       0 | udpo       
> 4 |
> NET | eth0    ---- | pcki   22736 | pcko   80243 | si   12 Mbps | so 5777 
> Mbps |
> NET | vlan100 ---- | pcki   22738 | pcko   80245 | si 9495 Kbps | so 5775 
> Mbps |
> 
> #atop from Dom0
> CPU | sys      57% | irq      39%   
> cpu | sys      58% | irq      41%  
> ..
> NET | vif1.0  ---- |  pcki  227727 | pcko  797502  | si   10 Mbps |  so 5743 
> Mbps 
> NET | vif2.0  ---- |  pcki  797748 | pcko  227717  | si 5736 Mbps |  so   12 
> Mbps 
> 
> 
> 
> 2) untagged by OVS interface (in OVS like "tag: 1002")
> #atop from VM  - untagged by OVS interface
> NET | transport    | tcpi    8495 | tcpo  163131 | udpi       0 | udpo       0
> NET | eth1    ---- | pcki    8495 | pcko   24718 | si 4485 Kbps | so   11 Gbps
> 
> #atop from Dom0
> CPU | sys      96% | irq       4%  
> cpu | sys      96% | irq       4% 
> ..
> NET | vif1.1  ---- |  pcki   75974 | pcko  247608  | si 3160 Kbps |  so   11 
> Gbps
> NET | vif2.1  ---- |  pcki  247616 | pcko   75971  | si   11 Gbps |  so 4011 
> Kbps 
> 
> 
> As you can see second variant have full netback sys load in DOM0. Second have 
> high number 
> of irq and high numbers of pcki/pcko.
> Is this behavior correct?

I'd have expected the second case to be lower overhead, which it is. I
would expect the first case to be higher overhead, which it is, but it
seems a lot higher than I would have handwavily expected -- I'm not sure
why vlan offload on the vif device should matter to that extent.

Wei, what do you think of implementing vif offload on the netback vif
devices? I don't necessarily mean over the wire protocol, although that
might be worth investigating separately, just at the netdev interface --
i.e. inserting the VLAN header into the ring as part of
xen_netbk_tx_build_gops() processing or whatever?

Ian.


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