netdev - Re: [PATCH RFC v3 0/5] Support fraglist GRO/GSO

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Message-ID: <CA+FuTSebcFKP4kedJYMXg9WTTxmcaVx_erCHuxTB==UNfNLNGQ@mail.gmail.com>
Date:   Thu, 19 Sep 2019 09:25:10 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Cc:     Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        Steffen Klassert <steffen.klassert@...unet.com>,
        Network Development <netdev@...r.kernel.org>,
        Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH RFC v3 0/5] Support fraglist GRO/GSO

On Thu, Sep 19, 2019 at 9:07 AM Marcelo Ricardo Leitner
<marcelo.leitner@...il.com> wrote:
>
> On Thu, Sep 19, 2019 at 08:55:22AM -0400, Willem de Bruijn wrote:
> > On Wed, Sep 18, 2019 at 12:58 PM Marcelo Ricardo Leitner
> > <marcelo.leitner@...il.com> wrote:
> > >
> > > On Wed, Sep 18, 2019 at 12:17:08PM -0400, Willem de Bruijn wrote:
> > > > On Wed, Sep 18, 2019 at 3:25 AM Steffen Klassert
> > > > <steffen.klassert@...unet.com> wrote:
> > > > >
> > > > > This patchset adds support to do GRO/GSO by chaining packets
> > > > > of the same flow at the SKB frag_list pointer. This avoids
> > > > > the overhead to merge payloads into one big packet, and
> > > > > on the other end, if GSO is needed it avoids the overhead
> > > > > of splitting the big packet back to the native form.
> > > > >
> > > > > Patch 1 Enables UDP GRO by default.
> > > > >
> > > > > Patch 2 adds a netdev feature flag to enable listifyed GRO,
> > > > > this implements one of the configuration options discussed
> > > > > at netconf 2019.
> > > > >
> > > > > Patch 3 adds a netdev software feature set that defaults to off
> > > > > and assigns the new listifyed GRO feature flag to it.
> > > > >
> > > > > Patch 4 adds the core infrastructure to do fraglist GRO/GSO.
> > > > >
> > > > > Patch 5 enables UDP to use fraglist GRO/GSO if configured and no
> > > > > GRO supported socket is found.
> > > >
> > > > Very nice feature, Steffen. Aside from questions around performance,
> > > > my only question is really how this relates to GSO_BY_FRAGS.
> > >
> > > They do the exact same thing AFAICT: they GSO according to a
> > > pre-formatted list of fragments/packets, and not to a specific size
> > > (such as MSS).
> > >
> > > >
> > > > More specifically, whether we can remove that in favor of using your
> > > > new skb_segment_list. That would actually be a big first step in
> > > > simplifying skb_segment back to something manageable.
> > >
> > > The main issue (that I know) on obsoleting GSO_BY_FRAGS is that
> > > dealing with frags instead of frag_list was considered easier to be
> > > offloaded, if ever attempted.  So this would be a step back on that
> > > aspect.  Other than this, it should be doable.
> >
> > But GSO_BY_FRAGS also uses frag_list, not frags?
>
> /me is scratching his head.
> My bad. I thought it was already using frags. Thanks.
>
> >
> > And list_skb->len for mss.
>
> Which stands more for 'current frag size', yes.
> (list_skb, not head_skb)

Great. I thought I missed something :)

Frags might be cheaper from an allocation point. If at some point
going down that road.

But in the meantime, it looks like we can handle these too with
skb_segment_list, then (not necessarily in the initial patch set).