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    • Ilya Maximets's avatar
      net: add initial support for AF_XDP network backend · cb039ef3
      Ilya Maximets authored 
      
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: default avatarIlya Maximets <i.maximets@ovn.org>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com> (docker/lcitool)
Signed-off-by: default avatarJason Wang <jasowang@redhat.com>
      cb039ef3
    • Ilya Maximets's avatar
      tests: bump libvirt-ci for libasan and libxdp · a6f376e9
      Ilya Maximets authored 
      
This pulls in the fixes for libasan version as well as support for
libxdp that will be used for af-xdp netdev in the next commits.

Signed-off-by: default avatarIlya Maximets <i.maximets@ovn.org>
Reviewed-by: default avatarDaniel P. Berrangé <berrange@redhat.com>
Signed-off-by: default avatarJason Wang <jasowang@redhat.com>
      a6f376e9
  11. Aug 28, 2023
  13. Jul 18, 2023
  15. Jul 17, 2023
  17. Jul 03, 2023
  19. May 16, 2023
    • Ani Sinha's avatar
      tests/lcitool: Add mtools and xorriso and remove genisoimage as dependencies · da900078
      Ani Sinha authored 
      
Bios bits avocado tests need mformat (provided by the mtools package) and
xorriso tools in order to run within gitlab CI containers. Add those
dependencies within the Dockerfiles so that containers can be built with
those tools present and bios bits avocado tests can be run there.

xorriso package conflicts with genisoimage package on some distributions.
Therefore, it is not possible to have both the packages at the same time
in the container image uniformly for all distribution flavors. Further,
on some distributions like RHEL, both xorriso and genisoimage
packages provide /usr/bin/genisoimage and on some other distributions like
Fedora, only genisoimage package provides the same utility.
Therefore, this change removes the dependency on geninsoimage for building
container images altogether keeping only xorriso package. At the same time,
cdrom-test.c is updated to use and check for existence of only xorrisofs.

Signed-off-by: default avatarAni Sinha <anisinha@redhat.com>
Message-Id: <20230504154611.85854-3-anisinha@redhat.com>
Reviewed-by: default avatarThomas Huth <thuth@redhat.com>
Reviewed-by: default avatarMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: default avatarThomas Huth <thuth@redhat.com>
      da900078
    • Ani Sinha's avatar
      tests: libvirt-ci: Update to commit 'c8971e90ac' to pull in mformat and xorriso · a19b119b
      Ani Sinha authored 
      
Pull in the following changes from lcitool:

* tests/lcitool/libvirt-ci 85487e1...c8971e9 (18):
  > mappings: add new package mappings for mformat and xorriso
  > docs: testing: Update contents with tox
  > .gitlab-ci.yml: Always test against installed lcitool
  > gitlab-ci.yml: Start using tox for testing
  > tox: Allow running with custom pytest options with {posargs}
  > gitignore: Add the default .tox directory
  > dev-requirements: Reference VM requirements
  > requirements: Add tox to dev-requirements.txt and drop pytest and flake
  > test-requirements: Rename to dev-requirements.txt
  > Add tox.ini configuration file
  > tests: commands: Consolidate the installed package/run from git tests
  > Add a pytest.ini
  > facts: targets: Drop Fedora 36 target
  > gitlab-ci.yml: Add Fedora 38 target
  > facts: targets: Add Fedora 38
  > facts: mappings: Drop 'zstd' mapping
  > facts: projects: nbdkit: Replace zstd mapping with libzstd
  > docs: mappings: Add a section on the preferred mapping naming scheme

Signed-off-by: default avatarAni Sinha <anisinha@redhat.com>
Message-Id: <20230504154611.85854-2-anisinha@redhat.com>
Reviewed-by: default avatarThomas Huth <thuth@redhat.com>
Reviewed-by: default avatarMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: default avatarThomas Huth <thuth@redhat.com>
      a19b119b
  21. Apr 27, 2023
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