Received-SPF: pass (google.com: domain of linux-kernel+bounces-156088-linux.lists.archive=gmail.com@vger.kernel.org designates 139.178.88.99 as permitted sender) client-ip=139.178.88.99;
Date: Tue, 23 Apr 2024 21:24:51 -0400
From: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
To: Felix Fietkau <nbd@nbd.name>, 
 Paolo Abeni <pabeni@redhat.com>, 
 Eric Dumazet <edumazet@google.com>
Cc: netdev@vger.kernel.org, 
 "David S. Miller" <davem@davemloft.net>, 
 Jakub Kicinski <kuba@kernel.org>, 
 David Ahern <dsahern@kernel.org>, 
 linux-kernel@vger.kernel.org
Message-ID: <66285f637bdec_1924cc2941b@willemb.c.googlers.com.notmuch>
In-Reply-To: <328ab7b3-4890-4e0d-8b9a-fed7700f1a6a@nbd.name>
References: <20240423094117.93206-1-nbd@nbd.name>
 <CANn89i+6xRe4V6aDmD-9EM0uD7A87f6rzg3S7Xq6-NaB_Mb4nw@mail.gmail.com>
 <63abfa26-d990-46c3-8982-3eaf7b8f8ee5@nbd.name>
 <CANn89iJZvoKVB+AK1_44gki2pHyigyMLXFkyevSQpH3iDbnCvw@mail.gmail.com>
 <7476374f-cf0c-45d0-8100-1b2cd2f290d5@nbd.name>
 <CANn89iLddm704LHPDnnoF2RbCfvrivAz0e6HTeiBARmvzoUBjA@mail.gmail.com>
 <ebe85dca-e0e9-4c55-a15d-20d340f66848@nbd.name>
 <97f10c8b5b615eac8f65d67ef10928d97b6b760d.camel@redhat.com>
 <328ab7b3-4890-4e0d-8b9a-fed7700f1a6a@nbd.name>
Subject: Re: [RFC] net: add TCP fraglist GRO support
Precedence: bulk
Mime-Version: 1.0
Content-Type: text/plain;
 charset=utf-8
Content-Transfer-Encoding: quoted-printable

Felix Fietkau wrote:
> On 23.04.24 16:34, Paolo Abeni wrote:
> > On Tue, 2024-04-23 at 14:23 +0200, Felix Fietkau wrote:
> >> On 23.04.24 14:11, Eric Dumazet wrote:
> >> > On Tue, Apr 23, 2024 at 1:55=E2=80=AFPM Felix Fietkau <nbd@nbd.nam=
e> wrote:
> >> > > =

> >> > > In the world of consumer-grade WiFi devices, there are a lot of =
chipsets
> >> > > with limited or nonexistent SG support, and very limited checksu=
m
> >> > > offload capabilities on Ethernet. The WiFi side of these devices=
 is
> >> > > often even worse. I think fraglist GRO is a decent fallback for =
the
> >> > > inevitable corner cases.
> >> > =

> >> > What about netfilter and NAT ? Are they okay with NETIF_F_FRAGLIST=
_GRO already ?
> >> > =

> >> > Many of these devices are probably using NAT.
> >> =

> >> In my tests, nftables NAT works just fine, both with and without =

> >> flowtable offloading. I didn't see anything in netfilter that would =
have =

> >> a problem with this.
> > =

> > I see you handle explicitly NAT changes in __tcpv4_gso_segment_csum()=
,
> > like the current UDP code.
> > =

> > The TCP header has many other fields that could be updated affecting
> > the TCP csum.
> > Handling every possible mutation looks cumbersome and will likely
> > reduce the performance benefits.
> > =

> > What is your plan WRT other TCP header fields update?
> =

> I think that should be easy enough to handle. My patch already only =

> combines packets where tcp_flag_word(th) is identical. So when =

> segmenting, I could handle all flags changes with a single =

> inet_proto_csum_replace4 call.
> =

> > Strictly WRT the patch, I guess it deserves to be split in series,
> > moving UDP helpers in common code and possibly factoring out more
> > helpers with separate patches.
> Will do.

A significant chunk of the complexity is in the
tcp[46]_check_fraglist_gro sk match. Is this heuristic worth the
complexity?

It seems that the platforms that will enable NETIF_F_FRAGLIST will
be mainly forwarding planes.

If keeping, this refinement can probably a separate follow-on patch in
the series too:

- refactor existing udp code
- add segmentation support to handle such packets on tx
- add coalescing support that starts building such packets on rx
- refine coalescing choice

> > e.g. in __tcpv4_gso_segment_csum() is quite similar
> > __udpv4_gso_segment_csum() - even too much, as the tcp csum should be=

> > always be updated when the ports or addresses change ;)
> =

> Will fix that.
> =

> Thanks,
> =

> - Felix