Re: [Qemu-discuss] E1000 & virtio will not respect set MTU

[Markus Kovero]

> As we can see here, packet length varies over what it should be, when
> using realtek, packet length is strictly 1448, which fits uplink fine
> and upload degration will not occur.
>
> This is not a pmtu problem either, same thing happens when pmtu
> discovery is disabled.
> This also happens on Windows, so I'm thinking its not distribution 
> related.
>
> Thanks for any assistance

Hi, It seems I have classical "oh, okay nevermind"-scenario here, had 
more time to look into it and it seems
I was too eager to jump on conclusions with strictly mtu-related issue, 
ignoring the fact I was merely witnessing gso/tso in operation without 
fully realizing that offloading can actually sink so deeply under 
virtualization layer and actually function (properly).
Performance degradation seems to come from other layers than kvm/qemu 
itself, I was able to benchmark speeds up to 3Gbps from virtual guest to 
host server using virtio.
I can't explain why realtek just works at this point, maybe due it's 
lacking some feature that is partly to blame here, have to dig deeper. 
(:

Thanks and sorry for mailing list noise(:

Markus Kovero