Re: [pull request][net-next 0/3] Mellanox, mlx5 GRE tunnel offloads

On Tue, Sep 5, 2017 at 4:14 AM, Hannes Frederic Sowa
[off-list ref] wrote:

Tom Herbert [off-list ref] writes:

quoted

There is absolutely no requirement in IP that packets are delivered in
order-- there never has been and there never will be! If the ULP, like
Ethernet encapsulation, requires in order deliver then it needs to
implement that itself like TCP, GRE, and other protocols ensure that
with sequence numbers and reassembly. All of these hoops we do make
sure that packets always follow the same path and are always in order
are done for benefit of middlebox devices like stateful firewalls that
have force us to adopt their concept of network architecture-- in the
long run this is self-defeating and kills our ability to innovate.

I'm not saying that we shouldn't consider legacy devices, but we
should scrutinize new development or solutions that perpetuate
incorrect design or bad assumptions.

So configure RSS per port and ensure no fragments are send to those
ports. This is possible and rather easy to do. It solves the problem
with legacy software and it spreads out packets for your applications.

It is not perfect but it is working and solves both problems.

Hannes,

I don't see how that solves anything. The purpose of RSS is to
distribute the load of protocol packets across queues. This needs to
work for UDP applications. For instance, if I were building a QUIC
server I'd want the sort of flow distribution that a TCP server would
give. You can't do that by configuring a few ports in the device.

If I were to suggest any HW change it would be to not do DPI on
fragments (MF or offset is set). This ensures that all packets of the
fragment train get hashed to the same queue and is on fact what RPS
has been doing for years without any complaints.

But even before I'd make that recommendation, I'd really like
understand what the problem actually is. The only thing I can garner
from this discussion and the Intel patch is that when fragments are
received OOO that is perceived as a problem. But the by the protocol
specification clearly says this is not a problem. So the questions
are: who is negatively affected by this? Is this a problem because
some artificial test that checks for everything to be in order is now
failing? Is this affecting real users? Is this an issue in the stack
or really with some implementation outside of the stack? If it is an
implementation outside of the stack, then are we just bandaid'ing over
someone else's incorrect implementation by patching the kernel (like
would have be the case if we change the kernel to interoperate with
Facebook's switch that couldn't handle OOO in twstate).

Thanks,
Tom

Bye,
Hannes