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  • Anton Anton anjo
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  1. Sep 20, 2023
    • Kevin Wolf's avatar
      block: Introduce bdrv_schedule_unref() · ac2ae233
      Kevin Wolf authored 
      
bdrv_unref() is called by a lot of places that need to hold the graph
lock (it naturally happens in the context of operations that change the
graph). However, bdrv_unref() takes the graph writer lock internally, so
it can't actually be called while already holding a graph lock without
causing a deadlock.

bdrv_unref() also can't just become GRAPH_WRLOCK because it drains the
node before closing it, and draining requires that the graph is
unlocked.

The solution is to defer deleting the node until we don't hold the lock
any more and draining is possible again.

Note that keeping images open for longer than necessary can create
problems, too: You can't open an image again before it is really closed
(if image locking didn't prevent it, it would cause corruption).
Reopening an image immediately happens at least during bdrv_open() and
bdrv_co_create().

In order to solve this problem, make sure to run the deferred unref in
bdrv_graph_wrunlock(), i.e. the first possible place where we can drain
again. This is also why bdrv_schedule_unref() is marked GRAPH_WRLOCK.

The output of iotest 051 is updated because the additional polling
changes the order of HMP output, resulting in a new "(qemu)" prompt in
the test output that was previously on a separate line and filtered out.

Signed-off-by: default avatarKevin Wolf <kwolf@redhat.com>
Message-ID: <20230911094620.45040-6-kwolf@redhat.com>
Reviewed-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: default avatarKevin Wolf <kwolf@redhat.com>
      ac2ae233
    • Kevin Wolf's avatar
      block: Take AioContext lock for bdrv_append() more consistently · 487b9187
      Kevin Wolf authored 
      
The documentation for bdrv_append() says that the caller must hold the
AioContext lock for bs_top. Change all callers to actually adhere to the
contract.

Signed-off-by: default avatarKevin Wolf <kwolf@redhat.com>
Reviewed-by: default avatarEric Blake <eblake@redhat.com>
Reviewed-by: default avatarEmanuele Giuseppe Esposito <eesposit@redhat.com>
Reviewed-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
Message-ID: <20230911094620.45040-5-kwolf@redhat.com>
Signed-off-by: default avatarKevin Wolf <kwolf@redhat.com>
      487b9187
  3. Sep 18, 2023
    • Gerd Hoffmann's avatar
      tests/acpi: disallow virt/SSDT.memhp updates · 0ec0767e
      Gerd Hoffmann authored 
      
Signed-off-by: default avatarGerd Hoffmann <kraxel@redhat.com>
      0ec0767e
    • Gerd Hoffmann's avatar
      tests/acpi: update virt/SSDT.memhp · 5f88dd43
      Gerd Hoffmann authored 
      
The edk2 update caused an address change:

 DefinitionBlock ("", "SSDT", 1, "BOCHS ", "NVDIMM", 0x00000001)
 {
     Scope (\_SB)
     {
         Device (NVDR)
         {
             Name (_HID, "ACPI0012" /* NVDIMM Root Device */)  // _HID: Hardware ID
             [ ... ]
         }
     }

-    Name (MEMA, 0x43D10000)
+    Name (MEMA, 0x43C90000)
 }

Signed-off-by: default avatarGerd Hoffmann <kraxel@redhat.com>
      5f88dd43
    • Gerd Hoffmann's avatar
      tests/acpi: allow virt/SSDT.memhp updates · 3808a058
      Gerd Hoffmann authored 
      
Signed-off-by: default avatarGerd Hoffmann <kraxel@redhat.com>
      3808a058
    • 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
    • Tomasz Dzieciol's avatar
      igb: RX payload guest writting refactoring · 17ccd016
      Tomasz Dzieciol authored 
      
Refactoring is done in preparation for support of multiple advanced
descriptors RX modes, especially packet-split modes.

Signed-off-by: default avatarTomasz Dzieciol <t.dzieciol@partner.samsung.com>
Reviewed-by: default avatarAkihiko Odaki <akihiko.odaki@daynix.com>
Tested-by: default avatarAkihiko Odaki <akihiko.odaki@daynix.com>
Signed-off-by: default avatarJason Wang <jasowang@redhat.com>
      17ccd016
  5. Sep 16, 2023
  7. Sep 12, 2023
  9. Sep 08, 2023
  11. Sep 07, 2023
  13. Sep 06, 2023
  15. Sep 01, 2023
  17. Aug 31, 2023