On Tue, 20 Apr 2021 15:49:44 +0200
Magnus Karlsson <magnus.karlsson@xxxxxxxxx> wrote:
> On Mon, Apr 19, 2021 at 8:56 AM Lorenzo Bianconi
> <lorenzo.bianconi@xxxxxxxxxx> wrote:
> >
> > > On Sun, Apr 18, 2021 at 6:18 PM Jesper Dangaard Brouer
> > > <brouer@xxxxxxxxxx> wrote:
> > > >
> > > > On Fri, 16 Apr 2021 16:27:18 +0200
> > > > Magnus Karlsson <magnus.karlsson@xxxxxxxxx> wrote:
> > > >
> > > > > On Thu, Apr 8, 2021 at 2:51 PM Lorenzo Bianconi <lorenzo@xxxxxxxxxx> 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?
> > >
> > > We will post them on the list as an RFC. Tirtha also added AF_XDP
> > > multi-frame support on top of Lorenzo's patches so we will send that
> > > one out as well. Will also rerun my experiments, properly document
> > > them and send out just to be sure that I did not make any mistake.
> >
> > ack, very cool, thx
>
> I have now run a new set of experiments on a Cascade Lake server at
> 2.1 GHz with turbo boost disabled. Two NICs: i40e and ice. The
> baseline is commit 5c507329000e ("libbpf: Clarify flags in ringbuf
> helpers") and Lorenzo's and Eelco's path set is their v8. First some
> runs with xdpsock (i.e. AF_XDP) in both 2-core mode (app on one core
> and the driver on another) and 1-core mode using busy_poll.
>
> xdpsock rxdrop throughput change with the multi-buffer patches without
> any driver changes:
> 1-core i40e: -0.5 to 0% 2-cores i40e: -0.5%
> 1-core ice: -2% 2-cores ice: -1 to -0.5%
>
> xdp_rxq_info -a XDP_DROP
> i40e: -4% ice: +8%
>
> xdp_rxq_info -a XDP_TX
> i40e: -10% ice: +9%
>
> The XDP results with xdp_rxq_info are just weird! I reran them three
> times, rebuilt and rebooted in between and I always get the same
> results. And I also checked that I am running on the correct NUMA node
> and so on. But I have a hard time believing them. Nearly +10% and -10%
> difference. Too much in my book. Jesper, could you please run the same
> and see what you get?
We of-cause have to find the root-cause of the +-10%, but let me drill
into what the 10% represent time/cycle wise. Using a percentage
difference is usually a really good idea as it implies a comparative
measure (something I always request people to do, as a single
performance number means nothing by itself).
For a zoom-in-benchmarks like these where the amount of code executed
is very small, the effect of removing or adding code can effect the
measurement a lot.
I can only do the tests for i40e, as I don't have ice hardware (but
Intel is working on fixing that ;-)).
xdp_rxq_info -a XDP_DROP
i40e: 33,417,775 pps
CPU is 100% used, so we can calculate nanosec used per packet:
29.92 nanosec (1/33417775*10^9)
2.1 GHz CPU = approx 63 CPU-cycles
You lost -4% performance in this case. This correspond to:
-1.2 nanosec (29.92*0.04) slower
(This could be cost of single func call overhead = 1.3 ns)
My measurement for XDP_TX:
xdp_rxq_info -a XDP_TX
28,278,722 pps
35.36 ns (1/28278722*10^9)
You lost -10% performance in this case:
-3.54 nanosec (35.36*0.10) slower
In XDP context 3.54 nanosec is a lot, as you can see it is 10% in this
zoom-in benchmark. We have to look at the details.
One detail/issue with i40e doing XDP_TX, is that I cannot verify that
packets are actually transmitted... not via exception tracepoint, not
via netstats, not via ethtool_stats.pl. Maybe all the packets are
getting (silently) drop in my tests...!?!
> The xdpsock numbers are more in the ballpark of
> what I would expect.
>
> Tirtha and I found some optimizations in the i40e
> multi-frame/multi-buffer support that we have implemented. Will test
> those next, post the results and share the code.
>
> > >
> > > Just note that I would really like for the multi-frame support to get
> > > in. I have lost count on how many people that have asked for it to be
> > > added to XDP and AF_XDP. So please check our implementation and
> > > improve it so we can get the overhead down to where we want it to be.
> >
> > sure, I will do.
> >
> > Regards,
> > Lorenzo
> >
> > >
> > > Thanks: Magnus
> > >
> > > > 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
--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
LinkedIn: http://www.linkedin.com/in/brouer
Running XDP on dev:i40e2 (ifindex:6) action:XDP_DROP options:read
XDP stats CPU pps issue-pps
XDP-RX CPU 2 33,417,775 0
XDP-RX CPU total 33,417,775
RXQ stats RXQ:CPU pps issue-pps
rx_queue_index 2:2 33,417,775 0
rx_queue_index 2:sum 33,417,775
Running XDP on dev:i40e2 (ifindex:6) action:XDP_TX options:swapmac
XDP stats CPU pps issue-pps
XDP-RX CPU 2 28,278,722 0
XDP-RX CPU total 28,278,722
RXQ stats RXQ:CPU pps issue-pps
rx_queue_index 2:2 28,278,726 0
rx_queue_index 2:sum 28,278,726
