[RFC] Patch to add Software/Generic Segmentation Offload (GSO) support in FreeBSD

[Stefano Garzarella]

Hi Freddie,
this is a preliminary version and, for now, we have not analyzed all
aspects.
Thanks for your suggestion. We will try to analyze how the GSO affects IPFW
as soon as possible.

Cheers,
Stefano

2014-09-18 17:27 GMT+02:00 Freddie Cash <fjwcash at gmail.com>:

> On Thu, Sep 18, 2014 at 7:16 AM, Stefano Garzarella <
> stefanogarzarella at gmail.com> wrote:
>
>> I saw the discussion about TSO, but the GSO is a software
>> implementation unrelated with the hardware.
>> Furthermore, if the TSO is enabled (and supported by the NIC), the GSO is
>> not executed, because is useless.
>>
>> After the execution of the GSO, the packets, that are passed to the device
>> driver, are smaller (or equal) than MTU, so the TSO is unnecessary. For
>> this reason the GSO doesn't look neither "ifp->if_hw_tsomax" nor hardware
>> segment limits.
>>
>> The GSO is very useful when you can't use the TSO.
>>
>
> ​How does GSO affect IPFW, specifically the libalias(3)-based, in-kernel
> NAT?  The ipfw(8) man page mentions that it doesn't play nicely with
> hardware-based TSO, and that one should disable TSO when using IPFW NAT.
>
> Will the software-based GSO play nicely with IPFW NAT?​  Will it make any
> difference to packet throughput through IPFW?
>
> Or is it still way too early in development to be worrying about such
> things?  :)
>
> --
> Freddie Cash
> fjwcash at gmail.com
>



-- 
*Stefano Garzarella*
stefano.garzarella at gmail.com