Re: [RFC] net: add TCP fraglist GRO support

[Felix Fietkau]

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 PM Felix Fietkau <nbd@xxxxxxxx> wrote:
> > > > 
> > > > In the world of consumer-grade WiFi devices, there are a lot of chipsets
> > > > with limited or nonexistent SG support, and very limited checksum
> > > > 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.

> 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