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Date:      Thu, 18 Sep 2014 08:27:47 -0700
From:      Freddie Cash <fjwcash@gmail.com>
To:        Stefano Garzarella <stefanogarzarella@gmail.com>
Cc:        Hans Petter Selasky <hps@selasky.org>, Adrian Chadd <adrian@freebsd.org>, "freebsd-net@freebsd.org" <freebsd-net@freebsd.org>, freebsd-current <freebsd-current@freebsd.org>, Luigi Rizzo <rizzo@iet.unipi.it>
Subject:   Re: [RFC] Patch to add Software/Generic Segmentation Offload (GSO) support in FreeBSD
Message-ID:  <CAOjFWZ73X=v6=KgeF%2BTpRCAe=KbXm1Yp3iKpKDeqyKK12Ejtwg@mail.gmail.com>
In-Reply-To: <CAO0mX5ZGGY5fMmc%2BTFrknFrGrErrB7fx=f%2BSDMRg7oTTVHTRVg@mail.gmail.com>
References:  <CAO0mX5bDoCe8oRNmd%2BUBbr4bJcgQEzhAQKyTsyxEQciyvGTdgQ@mail.gmail.com> <CAJ-VmomY7M2h2Bbuu5BXRUYFRMnKXezZfCNbNWGFHACuFwNDmg@mail.gmail.com> <CAO0mX5Zdt487=entnjrMjxpt%2BLhKTNkS=sUHsnyVDYr_PXyS7Q@mail.gmail.com> <5419EE95.40600@selasky.org> <CAO0mX5ZGGY5fMmc%2BTFrknFrGrErrB7fx=f%2BSDMRg7oTTVHTRVg@mail.gmail.com>

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On Thu, Sep 18, 2014 at 7:16 AM, Stefano Garzarella <
stefanogarzarella@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 devic=
e
> 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.
>

=E2=80=8BHow does GSO affect IPFW, specifically the libalias(3)-based, in-k=
ernel
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?=E2=80=8B  Will it ma=
ke any
difference to packet throughput through IPFW?

Or is it still way too early in development to be worrying about such
things?  :)

--=20
Freddie Cash
fjwcash@gmail.com



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