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  1. Sep 19, 2023
  3. Sep 18, 2023
    • Daniel Henrique Barboza's avatar
      MAINTAINERS: Nick Piggin PPC maintainer, other PPC changes · 0cbc34dc
      Daniel Henrique Barboza authored 
      
Update all relevant PowerPC entries as follows:

- Nick Piggin is promoted to Maintainer in all qemu-ppc subsystems.
  Nick has  been a solid contributor for the last couple of years and
  has the required knowledge and motivation to drive the boat.

- Greg Kurz is being removed from all qemu-ppc entries. Greg has moved
  to other areas of interest and will retire from qemu-ppc.  Thanks Mr
  Kurz for all the years of service.

- David Gibson was removed as 'Reviewer' from PowerPC TCG CPUs and PPC
  KVM CPUs. Change done per his request.

- Daniel Barboza downgraded from 'Maintainer' to 'Reviewer' in sPAPR and
  PPC KVM CPUs. It has been a long since I last touched those areas and
  it's not justified to be kept as maintainer in them.

- Cedric Le Goater and Daniel Barboza removed as 'Reviewer' in VOF. We
  don't have the required knowledge to justify it.

- VOF support downgraded from 'Maintained' to 'Odd Fixes' since it
  better reflects the current state of the subsystem.

Acked-by: default avatarCédric Le Goater <clg@kaod.org>
Acked-by: default avatarGreg Kurz <groug@kaod.org>
Reviewed-by: default avatarPhilippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: default avatarAlex Bennée <alex.bennee@linaro.org>
Reviewed-by: default avatarHarsh Prateek Bora <harshpb@linux.ibm.com>
Acked-by: default avatarDavid Gibson <david@gibson.dropbear.id.au>
Acked-by: default avatarNicholas Piggin <npiggin@gmail.com>
Message-ID: <20230915110507.194762-1-danielhb413@gmail.com>
Signed-off-by: default avatarDaniel Henrique Barboza <danielhb413@gmail.com>
      0cbc34dc
    • 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
  5. Sep 08, 2023
  7. Sep 07, 2023
  9. Sep 06, 2023
  11. Aug 31, 2023
  13. Aug 02, 2023
  15. Jul 12, 2023
  17. Jul 10, 2023
  19. Jul 08, 2023
  21. Jul 06, 2023
  23. Jul 03, 2023
  25. Jun 30, 2023
  27. Jun 28, 2023
  29. Jun 27, 2023
  31. Jun 25, 2023
  33. Jun 22, 2023
  35. Jun 13, 2023
  37. Jun 08, 2023
  39. Jun 06, 2023
  41. Jun 05, 2023
  43. Jun 01, 2023
    • Stefan Hajnoczi's avatar
      block: add blk_io_plug_call() API · 41abca8c
      Stefan Hajnoczi authored 
      
Introduce a new API for thread-local blk_io_plug() that does not
traverse the block graph. The goal is to make blk_io_plug() multi-queue
friendly.

Instead of having block drivers track whether or not we're in a plugged
section, provide an API that allows them to defer a function call until
we're unplugged: blk_io_plug_call(fn, opaque). If blk_io_plug_call() is
called multiple times with the same fn/opaque pair, then fn() is only
called once at the end of the function - resulting in batching.

This patch introduces the API and changes blk_io_plug()/blk_io_unplug().
blk_io_plug()/blk_io_unplug() no longer require a BlockBackend argument
because the plug state is now thread-local.

Later patches convert block drivers to blk_io_plug_call() and then we
can finally remove .bdrv_co_io_plug() once all block drivers have been
converted.

Signed-off-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: default avatarEric Blake <eblake@redhat.com>
Reviewed-by: default avatarStefano Garzarella <sgarzare@redhat.com>
Acked-by: default avatarKevin Wolf <kwolf@redhat.com>
Message-id: 20230530180959.1108766-2-stefanha@redhat.com
Signed-off-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
      41abca8c
  45. May 26, 2023
  47. May 24, 2023
  49. May 23, 2023