Subject: Re: [PATCH v8 bpf-next 00/14] mvneta: introduce XDP multi-buffer support

From: Jesper Dangaard Brouer <[email-masked]>
Date: Sun, 18 Apr 2021 18:18:01 +0200

On Fri, 16 Apr 2021 16:27:18 +0200
Magnus Karlsson <[email-masked]> wrote:

> On Thu, Apr 8, 2021 at 2:51 PM Lorenzo Bianconi <[email-masked]> wrote:
> >
> > This series introduce XDP multi-buffer support. The mvneta driver is
> > the first to support these new "non-linear" xdp_{buff,frame}. Reviewers
> > please focus on how these new types of xdp_{buff,frame} packets
> > traverse the different layers and the layout design. It is on purpose
> > that BPF-helpers are kept simple, as we don't want to expose the
> > internal layout to allow later changes.
> >
> > For now, to keep the design simple and to maintain performance, the XDP
> > BPF-prog (still) only have access to the first-buffer. It is left for
> > later (another patchset) to add payload access across multiple buffers.
> > This patchset should still allow for these future extensions. The goal
> > is to lift the XDP MTU restriction that comes with XDP, but maintain
> > same performance as before.
[...]
> >
> > [0] https://netdevconf.info/0x14/session.html?talk-the-path-to-tcp-4k-mtu-and-rx-zerocopy
> > [1] https://github.com/xdp-project/xdp-project/blob/master/areas/core/xdp-multi-buffer01-design.org
> > [2] https://netdevconf.info/0x14/session.html?tutorial-add-XDP-support-to-a-NIC-driver (XDPmulti-buffers section)  
> 
> Took your patches for a test run with the AF_XDP sample xdpsock on an
> i40e card and the throughput degradation is between 2 to 6% depending
> on the setup and microbenchmark within xdpsock that is executed. And
> this is without sending any multi frame packets. Just single frame
> ones. Tirtha made changes to the i40e driver to support this new
> interface so that is being included in the measurements.

Could you please share Tirtha's i40e support patch with me?

I would like to reproduce these results in my testlab, in-order to
figure out where the throughput degradation comes from.

> What performance do you see with the mvneta card? How much are we
> willing to pay for this feature when it is not being used or can we in
> some way selectively turn it on only when needed?

Well, as Daniel says performance wise we require close to /zero/
additional overhead, especially as you state this happens when sending
a single frame, which is a base case that we must not slowdown.

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer