[ovs-discuss] Xen/OVS - VLAN offloading

[Jesse Gross]

On Fri, May 31, 2013 at 5:17 PM, Eugene Istomin <e.istomin at edss.ee> wrote:
>> This is dependent on the hypervisor and not being restricted by OVS.
>> However, the direct benefits of vlan offloading are very minimal and
>> are really only useful in relation to enabling other offloads.
>
> In my testbed results are not minimal (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?

You are seeing the result of TSO not functioning in the presence of
vlans. This is one of the other offloads that I was referring to
before but it's not directly the result of the features that you
showed. Regardless, this is a limitation of Xen and not something that
OVS affects.