mirror_qemu/scripts
Ilya Maximets cb039ef3d9 net: add initial support for AF_XDP network backend
AF_XDP is a network socket family that allows communication directly
with the network device driver in the kernel, bypassing most or all
of the kernel networking stack.  In the essence, the technology is
pretty similar to netmap.  But, unlike netmap, AF_XDP is Linux-native
and works with any network interfaces without driver modifications.
Unlike vhost-based backends (kernel, user, vdpa), AF_XDP doesn't
require access to character devices or unix sockets.  Only access to
the network interface itself is necessary.

This patch implements a network backend that communicates with the
kernel by creating an AF_XDP socket.  A chunk of userspace memory
is shared between QEMU and the host kernel.  4 ring buffers (Tx, Rx,
Fill and Completion) are placed in that memory along with a pool of
memory buffers for the packet data.  Data transmission is done by
allocating one of the buffers, copying packet data into it and
placing the pointer into Tx ring.  After transmission, device will
return the buffer via Completion ring.  On Rx, device will take
a buffer form a pre-populated Fill ring, write the packet data into
it and place the buffer into Rx ring.

AF_XDP network backend takes on the communication with the host
kernel and the network interface and forwards packets to/from the
peer device in QEMU.

Usage example:

  -device virtio-net-pci,netdev=guest1,mac=00:16:35:AF:AA:5C
  -netdev af-xdp,ifname=ens6f1np1,id=guest1,mode=native,queues=1

XDP program bridges the socket with a network interface.  It can be
attached to the interface in 2 different modes:

1. skb - this mode should work for any interface and doesn't require
         driver support.  With a caveat of lower performance.

2. native - this does require support from the driver and allows to
            bypass skb allocation in the kernel and potentially use
            zero-copy while getting packets in/out userspace.

By default, QEMU will try to use native mode and fall back to skb.
Mode can be forced via 'mode' option.  To force 'copy' even in native
mode, use 'force-copy=on' option.  This might be useful if there is
some issue with the driver.

Option 'queues=N' allows to specify how many device queues should
be open.  Note that all the queues that are not open are still
functional and can receive traffic, but it will not be delivered to
QEMU.  So, the number of device queues should generally match the
QEMU configuration, unless the device is shared with something
else and the traffic re-direction to appropriate queues is correctly
configured on a device level (e.g. with ethtool -N).
'start-queue=M' option can be used to specify from which queue id
QEMU should start configuring 'N' queues.  It might also be necessary
to use this option with certain NICs, e.g. MLX5 NICs.  See the docs
for examples.

In a general case QEMU will need CAP_NET_ADMIN and CAP_SYS_ADMIN
or CAP_BPF capabilities in order to load default XSK/XDP programs to
the network interface and configure BPF maps.  It is possible, however,
to run with no capabilities.  For that to work, an external process
with enough capabilities will need to pre-load default XSK program,
create AF_XDP sockets and pass their file descriptors to QEMU process
on startup via 'sock-fds' option.  Network backend will need to be
configured with 'inhibit=on' to avoid loading of the program.
QEMU will need 32 MB of locked memory (RLIMIT_MEMLOCK) per queue
or CAP_IPC_LOCK.

There are few performance challenges with the current network backends.

First is that they do not support IO threads.  This means that data
path is handled by the main thread in QEMU and may slow down other
work or may be slowed down by some other work.  This also means that
taking advantage of multi-queue is generally not possible today.

Another thing is that data path is going through the device emulation
code, which is not really optimized for performance.  The fastest
"frontend" device is virtio-net.  But it's not optimized for heavy
traffic either, because it expects such use-cases to be handled via
some implementation of vhost (user, kernel, vdpa).  In practice, we
have virtio notifications and rcu lock/unlock on a per-packet basis
and not very efficient accesses to the guest memory.  Communication
channels between backend and frontend devices do not allow passing
more than one packet at a time as well.

Some of these challenges can be avoided in the future by adding better
batching into device emulation or by implementing vhost-af-xdp variant.

There are also a few kernel limitations.  AF_XDP sockets do not
support any kinds of checksum or segmentation offloading.  Buffers
are limited to a page size (4K), i.e. MTU is limited.  Multi-buffer
support implementation for AF_XDP is in progress, but not ready yet.
Also, transmission in all non-zero-copy modes is synchronous, i.e.
done in a syscall.  That doesn't allow high packet rates on virtual
interfaces.

However, keeping in mind all of these challenges, current implementation
of the AF_XDP backend shows a decent performance while running on top
of a physical NIC with zero-copy support.

Test setup:

2 VMs running on 2 physical hosts connected via ConnectX6-Dx card.
Network backend is configured to open the NIC directly in native mode.
The driver supports zero-copy.  NIC is configured to use 1 queue.

Inside a VM - iperf3 for basic TCP performance testing and dpdk-testpmd
for PPS testing.

iperf3 result:
 TCP stream      : 19.1 Gbps

dpdk-testpmd (single queue, single CPU core, 64 B packets) results:
 Tx only         : 3.4 Mpps
 Rx only         : 2.0 Mpps
 L2 FWD Loopback : 1.5 Mpps

In skb mode the same setup shows much lower performance, similar to
the setup where pair of physical NICs is replaced with veth pair:

iperf3 result:
  TCP stream      : 9 Gbps

dpdk-testpmd (single queue, single CPU core, 64 B packets) results:
  Tx only         : 1.2 Mpps
  Rx only         : 1.0 Mpps
  L2 FWD Loopback : 0.7 Mpps

Results in skb mode or over the veth are close to results of a tap
backend with vhost=on and disabled segmentation offloading bridged
with a NIC.

Signed-off-by: Ilya Maximets <i.maximets@ovn.org>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com> (docker/lcitool)
Signed-off-by: Jason Wang <jasowang@redhat.com>
2023-09-18 14:36:13 +08:00
..
ci net: add initial support for AF_XDP network backend 2023-09-18 14:36:13 +08:00
coccinelle cleanup: Tweak and re-run return_directly.cocci 2022-12-14 16:19:35 +01:00
codeconverter scripts/: spelling fixes 2023-09-08 13:08:52 +03:00
coverage scripts/coverage: initial coverage comparison script 2023-04-04 15:16:29 +01:00
coverity-scan coverity: the definitive COMPONENTS.md update 2023-05-18 08:53:51 +02:00
kvm vmxcap: add tertiary execution controls 2022-05-12 14:23:19 +02:00
modules scripts/modules/module_block: Use Python 3 interpreter & add pseudo-main 2020-05-31 13:56:46 +02:00
oss-fuzz scripts/: spelling fixes 2023-09-08 13:08:52 +03:00
performance scripts/: spelling fixes 2023-09-08 13:08:52 +03:00
qapi scripts/: spelling fixes 2023-09-08 13:08:52 +03:00
qemu-guest-agent
qemugdb scripts/gdb: implement 'qemu bt' 2021-01-12 12:38:03 +01:00
qmp python: rename qemu.aqmp to qemu.qmp 2022-04-21 11:01:00 -04:00
simplebench scripts/: spelling fixes 2023-09-08 13:08:52 +03:00
tracetool trace: remove control-vcpu.h 2023-06-01 11:05:05 -04:00
analyse-9p-simpletrace.py drop "from __future__ import print_function" 2020-02-07 15:15:16 +01:00
analyse-locks-simpletrace.py drop "from __future__ import print_function" 2020-02-07 15:15:16 +01:00
analyze-inclusions scripts/analyze-inclusions: drop qemu-common.h from analysis 2022-04-21 16:56:55 +04:00
analyze-migration.py analyze-migration.py: fix extract contents ('-x') errors 2021-10-23 20:28:56 +02:00
archive-source.sh meson: subprojects: replace berkeley-{soft,test}float-3 with wraps 2023-06-06 16:30:01 +02:00
block-coroutine-wrapper.py block-coroutine-wrapper: Take AioContext lock in no_co_wrappers 2023-05-30 17:21:23 +02:00
check_sparse.py meson: move sparse detection to Meson and rewrite check_sparse.py 2020-10-04 18:36:23 +02:00
checkpatch.pl scripts/: spelling fixes 2023-09-08 13:08:52 +03:00
clean-header-guards.pl disas: Remove libvixl disassembler 2022-07-05 10:15:49 +02:00
clean-includes scripts/clean-includes: Improve --git commit message 2023-02-08 07:16:23 +01:00
cleanup-trace-events.pl scripts/cleanup-trace-events: Emit files in alphabetical order 2020-09-09 17:17:00 +01:00
cocci-macro-file.h compiler.h: replace QEMU_NORETURN with G_NORETURN 2022-04-21 17:03:51 +04:00
cpu-x86-uarch-abi.py python: rename qemu.aqmp to qemu.qmp 2022-04-21 11:01:00 -04:00
decodetree.py tests/decode: Suppress "error: " string for expected-failure tests 2023-07-25 10:56:52 +01:00
device-crash-test Revert "tests: Use separate virtual environment for avocado" 2023-08-28 09:55:48 +02:00
disas-objdump.pl
dump-guest-memory.py drop "from __future__ import print_function" 2020-02-07 15:15:16 +01:00
entitlement.sh scripts/entitlement.sh: Use backward-compatible cp flags 2021-11-30 22:25:58 +01:00
extract-vsssdk-headers
feature_to_c.sh Add missing include statement for global xml_builtin 2022-11-06 09:48:42 +01:00
fix-multiline-comments.sh docs: move CODING_STYLE into the developer documentation 2021-02-24 11:05:21 +00:00
gensyscalls.sh linux-user: Add LoongArch syscall support 2022-07-04 11:08:57 +05:30
get_maintainer.pl get_maintainer: update repo URL to GitLab 2021-02-09 20:53:56 +00:00
git-submodule.sh scripts/git-submodule.sh: Don't rely on non-POSIX 'read' behaviour 2023-07-25 10:56:51 +01:00
git.orderfile scripts/git.orderfile: Display MAINTAINERS changes first 2023-01-13 16:22:57 +01:00
hxtool meson: generate hxtool files 2020-08-21 06:30:14 -04:00
kernel-doc scripts/kernel-doc: strip QEMU_ from function definitions 2021-03-24 14:24:40 +00:00
make-config-poison.sh exec/poison: Do not poison CONFIG_SOFTMMU 2023-06-05 12:04:29 -07:00
make-release meson: subprojects: replace berkeley-{soft,test}float-3 with wraps 2023-06-06 16:30:01 +02:00
meson-buildoptions.py scripts: make sure scripts are invoked via $(PYTHON) 2023-05-19 20:40:29 +02:00
meson-buildoptions.sh net: add initial support for AF_XDP network backend 2023-09-18 14:36:13 +08:00
meson.build scripts: add a XML preprocessor script 2023-06-27 17:08:56 +02:00
minikconf.py meson: infrastructure for building emulators 2020-08-21 06:30:17 -04:00
modinfo-collect.py scripts: make sure scripts are invoked via $(PYTHON) 2023-05-19 20:40:29 +02:00
modinfo-generate.py scripts: make sure scripts are invoked via $(PYTHON) 2023-05-19 20:40:29 +02:00
mtest2make.py mtest2make.py: teach suite name that are just "PROJECT" 2023-04-20 11:17:34 +02:00
nsis.py scripts/nsis.py: Automatically package required DLLs of QEMU executables 2022-10-31 10:06:11 +01:00
probe-gdb-support.py scripts: make sure scripts are invoked via $(PYTHON) 2023-05-19 20:40:29 +02:00
qapi-gen.py qapi: move generator entrypoint into package 2020-10-10 11:37:47 +02:00
qemu-binfmt-conf.sh scripts/qemu-binfmt-conf: Add LoongArch to qemu_get_family() 2022-07-05 16:17:53 +05:30
qemu-gdb.py scripts/gdb: implement 'qemu bt' 2021-01-12 12:38:03 +01:00
qemu-stamp.py meson, configure: move --with-pkgversion, CONFIG_STAMP to meson 2022-05-07 07:46:58 +02:00
qemu-trace-stap qemu-trace-stap: changing SYSTEMTAP_TAPSET considered harmful. 2021-07-12 17:37:06 +01:00
qemu-version.sh build-sys: fix git version from -version 2020-10-12 11:50:23 -04:00
qom-cast-macro-clean-cocci-gen.py scripts: Add qom-cast-macro-clean-cocci-gen.py 2023-06-05 20:48:34 +02:00
refresh-pxe-roms.sh
render_block_graph.py python: rename qemu.aqmp to qemu.qmp 2022-04-21 11:01:00 -04:00
replay-dump.py scripts/: spelling fixes 2023-09-08 13:08:52 +03:00
shaderinclude.py build-sys: fix crlf-ending C code 2023-02-02 10:44:23 +00:00
signrom.py drop "from __future__ import print_function" 2020-02-07 15:15:16 +01:00
simpletrace.py docs: fix references to docs/devel/tracing.rst 2021-06-02 06:51:09 +02:00
symlink-install-tree.py Add information how to fix common build error on Windows in symlink-install-tree 2023-05-16 09:14:18 +02:00
tracetool.py tracetool: add output filename command-line argument 2021-01-04 14:24:58 +00:00
u2f-setup-gen.py scripts: Add u2f-setup-gen script 2020-08-31 08:23:39 +02:00
undefsym.py build: fix macOS --enable-modules build 2020-10-22 11:53:52 -04:00
update-linux-headers.sh update-linux-headers.sh: Add missing kernel headers. 2023-04-28 14:03:52 +02:00
update-mips-syscall-args.sh linux-user, mips: update syscall-args-o32.c.inc to Linux v5.13 2021-07-13 13:59:59 +02:00
update-syscalltbl.sh linux-user, scripts: add a script to update syscall.tbl 2020-03-20 16:02:00 +01:00
userfaultfd-wrlat.py migration: introduce 'userfaultfd-wrlat.py' script 2021-02-08 11:19:51 +00:00
vmstate-static-checker.py vmstate-static-checker: Recognize "num" field 2023-04-27 10:18:26 +02:00
xen-detect.c xen: Drop support for Xen versions below 4.7.1 2023-06-07 15:07:10 +01:00
xml-preprocess-test.py scripts: add a XML preprocessor script 2023-06-27 17:08:56 +02:00
xml-preprocess.py scripts: add a XML preprocessor script 2023-06-27 17:08:56 +02:00