Re: [PATCH 0/8] net: Add passt netdev backend

[Jason Wang <jasowang@redhat.com>]

On Wed, Jun 18, 2025 at 4:39 PM Laurent Vivier <lvivier@redhat.com> wrote:
>
> This series introduces support for passt as a new network backend for
> QEMU.
>
> passt is a modern, unprivileged, user-mode networking solution that
> provides guest connectivity by launching an external helper process. This
> series adds the core backend and integrates it with vhost-user for
> high-performance, accelerated networking.
>
> The series is structured to first improve the general networking code
> before adding the new feature. The first patch extracts from the stream
> backend the functions that will be reused in the passt backend. The
> following patches are a preparatory refactoring to decouple the generic
> vhost layer from specific backend implementations (tap, vhost-user, etc.).
> This is achieved by replacing hardcoded type checks with a callback-based
> system in NetClientInfo, making the vhost infrastructure more modular and
> extensible.
>
> With the refactoring in place, subsequent patches introduce the passt
> backend itself, reusing the generic stream handling logic. The final
> patch adds vhost-user support to passt, which plugs cleanly into the
> newly refactored vhost layer.
>
> Some benchmarks:
>
>  Reference '-net user':
>
>   -net user,hostfwd=tcp::10001-:10001
>
>     iperf3 -c localhost -p 10001  -t 60 -4
>
>     [ ID] Interval           Transfer     Bitrate         Retr
>     [  5]   0.00-60.00  sec  14.2 GBytes  2.03 Gbits/sec    1            sender
>     [  5]   0.00-60.00  sec  14.2 GBytes  2.03 Gbits/sec                  receiver
>
>  New backend '-netdev passt'
>
>   -netdev passt,vhost-user=off,tcp-ports=10001
>
>     iperf3 -c localhost -p 10001  -t 60 -4
>
>     [ ID] Interval           Transfer     Bitrate         Retr
>     [  5]   0.00-60.00  sec  27.1 GBytes  3.88 Gbits/sec    0            sender
>     [  5]   0.00-60.03  sec  27.1 GBytes  3.88 Gbits/sec                  receiver
>
>   -netdev passt,vhost-user=on,tcp-ports=10001
>
>     iperf3 -c localhost -p 10001  -t 60 -4
>
>     [ ID] Interval           Transfer     Bitrate         Retr
>     [  5]   0.00-60.00  sec   224 GBytes  32.1 Gbits/sec    4            sender
>     [  5]   0.00-60.05  sec   224 GBytes  32.0 Gbits/sec                  receiver

Do we have latency numbers of even PPS?

Thanks

>
> Thanks,
> Laurent
>
> Laurent Vivier (8):
>   net: Refactor stream logic for reuse in '-net passt'
>   net: Define net_client_set_link()
>   net: Introduce helper to identify vhost-user clients
>   net: Add get_vhost_net callback to NetClientInfo
>   net: Add get_acked_features callback to NetClientInfo
>   net: Add save_acked_features callback to NetClientInfo
>   net: Add passt network backend
>   net/passt: Implement vhost-user backend support
>
>  hmp-commands.hx          |   3 +
>  hw/net/vhost_net-stub.c  |   1 -
>  hw/net/vhost_net.c       |  89 ++---
>  hw/net/virtio-net.c      |  18 +-
>  include/net/net.h        |  12 +
>  include/net/tap.h        |   3 -
>  include/net/vhost-user.h |  19 --
>  include/net/vhost-vdpa.h |   2 -
>  meson.build              |   6 +
>  meson_options.txt        |   2 +
>  net/clients.h            |   4 +
>  net/hub.c                |   3 +
>  net/meson.build          |   6 +-
>  net/net.c                |  55 ++-
>  net/passt.c              | 718 +++++++++++++++++++++++++++++++++++++++
>  net/stream.c             | 282 ++++-----------
>  net/stream_data.c        | 193 +++++++++++
>  net/stream_data.h        |  31 ++
>  net/tap-win32.c          |   5 -
>  net/tap.c                |  20 +-
>  net/vhost-user-stub.c    |   1 -
>  net/vhost-user.c         |  22 +-
>  net/vhost-vdpa.c         |   4 +-
>  qapi/net.json            | 121 +++++++
>  qemu-options.hx          |  18 +
>  25 files changed, 1293 insertions(+), 345 deletions(-)
>  delete mode 100644 include/net/vhost-user.h
>  create mode 100644 net/passt.c
>  create mode 100644 net/stream_data.c
>  create mode 100644 net/stream_data.h
>
> --
> 2.49.0
>
>