Re: large packet support in netfront driver and guest network throughput

[annie li <annie.li@oracle.com>]

On 2013-9-18 1:53, Anirban Chakraborty wrote:
>
> On 9/17/13 1:25 AM, "Wei Liu" <wei.liu2@citrix.com> wrote:
>
>> On Tue, Sep 17, 2013 at 10:09:21AM +0800, annie li wrote:
>>> <snip>
>>>>> I tried dom0 to dom0 and I got 9.4 Gbps, which is what I expected
>>>>> (with GRO turned on in the physical interface). However, when I run
>>>>> guest to guest, things fall off. Is large packet not supported in
>>>>> netfront? I thought otherwise. I looked at the code and I do not see
>>>>> any call to napi_gro_receive(), rather it is using
>>>>> netif_receive_skb(). netback seems to be sending GSO packets to the
>>>>> netfront, but it is being segmented to 1500 byte (as it appears from
>>>>> the tcpdump).
>>>>>
>>>> OK, I get your problem.
>>>>
>>>> Indeed netfront doesn't make use of GRO API at the moment.
>>> This is true.
>>> But I am wondering why large packet is not segmented into mtu size
>>> with upstream kernel? I did see large packets with upsteam kernel on
>>> receive guest(test between 2 domus on same host).
>>>
>> I think Anirban's setup is different. The traffic is from a DomU on
>> another host.
>>
>> I will need to setup testing environment with 10G link to test this.
>>
>> Anirban, can you share your setup, especially DomU kernel version, are
>> you using upstream kernel in DomU?
> Sure..
> I have two hosts, say h1 and h2 running XenServer 6.1.
> h1 running Centos 6.4, 64bit kernel, say guest1 and h2 running identical
> guest, guest2.
>
> iperf server is running on guest1 with iperf client connecting from guest2.
>
> I haven't tried with upstream kernel yet. However, what I found out is
> that the netback on the receiving host is transmitting GSO segments to the
> guest (guest1), but the packets are segmented at the netfront interface.

Did you try the guests on same host in your environment?

>
> Annie's setup has both the guests running on the same host, in which case
> packets are looped back.

If guests does not segment packets for same host case, it should not do 
segment for different host case. For current upstream, Netback->netfront 
mechanism does not treat differently for these two cases.

Thanks
Annie