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Björn Töpel says:
====================
This patch serie introduces zerocopy (ZC) support for
AF_XDP. Programs using AF_XDP sockets will now receive RX packets
without any copies and can also transmit packets without incurring any
copies. No modifications to the application are needed, but the NIC
driver needs to be modified to support ZC. If ZC is not supported by
the driver, the modes introduced in the AF_XDP patch will be
used. Using ZC in our micro benchmarks results in significantly
improved performance as can be seen in the performance section later
in this cover letter.
Note that for an untrusted application, HW packet steering to a
specific queue pair (the one associated with the application) is a
requirement when using ZC, as the application would otherwise be able
to see other user space processes' packets. If the HW cannot support
the required packet steering you need to use the XDP_SKB mode or the
XDP_DRV mode without ZC turned on. The XSKMAP introduced in the AF_XDP
patch set can be used to do load balancing in that case.
For benchmarking, you can use the xdpsock application from the AF_XDP
patch set without any modifications. Say that you would like your UDP
traffic from port 4242 to end up in queue 16, that we will enable
AF_XDP on. Here, we use ethtool for this:
ethtool -N p3p2 rx-flow-hash udp4 fn
ethtool -N p3p2 flow-type udp4 src-port 4242 dst-port 4242 \
action 16
Running the rxdrop benchmark in XDP_DRV mode with zerocopy can then be
done using:
samples/bpf/xdpsock -i p3p2 -q 16 -r -N
We have run some benchmarks on a dual socket system with two Broadwell
E5 2660 @ 2.0 GHz with hyperthreading turned off. Each socket has 14
cores which gives a total of 28, but only two cores are used in these
experiments. One for TR/RX and one for the user space application. The
memory is DDR4 @ 2133 MT/s (1067 MHz) and the size of each DIMM is
8192MB and with 8 of those DIMMs in the system we have 64 GB of total
memory. The compiler used is gcc (Ubuntu 7.3.0-16ubuntu3) 7.3.0. The
NIC is Intel I40E 40Gbit/s using the i40e driver.
Below are the results in Mpps of the I40E NIC benchmark runs for 64
and 1500 byte packets, generated by a commercial packet generator HW
outputing packets at full 40 Gbit/s line rate. The results are without
retpoline so that we can compare against previous numbers.
AF_XDP performance 64 byte packets. Results from the AF_XDP V3 patch
set are also reported for ease of reference. The numbers within
parantheses are from the RFC V1 ZC patch set.
Benchmark XDP_SKB XDP_DRV XDP_DRV with zerocopy
rxdrop 2.9* 9.6* 21.1(21.5)
txpush 2.6* - 22.0(21.6)
l2fwd 1.9* 2.5* 15.3(15.0)
AF_XDP performance 1500 byte packets:
Benchmark XDP_SKB XDP_DRV XDP_DRV with zerocopy
rxdrop 2.1* 3.3* 3.3(3.3)
l2fwd 1.4* 1.8* 3.1(3.1)
* From AF_XDP V3 patch set and cover letter.
So why do we not get higher values for RX similar to the 34 Mpps we
had in AF_PACKET V4? We made an experiment running the rxdrop
benchmark without using the xdp_do_redirect/flush infrastructure nor
using an XDP program (all traffic on a queue goes to one
socket). Instead the driver acts directly on the AF_XDP socket. With
this we got 36.9 Mpps, a significant improvement without any change to
the uapi. So not forcing users to have an XDP program if they do not
need it, might be a good idea. This measurement is actually higher
than what we got with AF_PACKET V4.
XDP performance on our system as a base line:
64 byte packets:
XDP stats CPU pps issue-pps
XDP-RX CPU 16 32.3M 0
1500 byte packets:
XDP stats CPU pps issue-pps
XDP-RX CPU 16 3.3M 0
The structure of the patch set is as follows:
Patches 1-3: Plumbing for AF_XDP ZC support
Patches 4-5: AF_XDP ZC for RX
Patches 6-7: AF_XDP ZC for TX
Patch 8-10: ZC support for i40e.
Patch 11: Use the bind flags in sample application to force TX skb
path when -S is providedd on the command line.
This patch set is based on the new uapi introduced in "AF_XDP: bug
fixes and descriptor changes". You need to apply that patch set
first, before applying this one.
We based this patch set on bpf-next commit
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.