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

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Fri, May 31, 2013 at 09:46:10AM +0100, Ian Campbell wrote:
> 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?
> 

Possibly, by inserting the vlan tag into an extra info slot.


Wei.

> Ian.

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