[PATCH v3 0/6] vhost-user: Add multiqueue support

[Laurent Vivier <lvivier@redhat.com>]

This series implements multiqueue support for vhost-user mode, allowing passt
to utilize multiple queue pairs for improved network throughput when used with
multi-CPU guest VMs. While this version uses a single thread for packet
processing, it enables the guest kernel to distribute network traffic across
multiple queues and vCPUs.

The implementation advertises support for up to 16 queue pairs (32 virtqueues)
by setting VIRTIO_NET_F_MQ and VHOST_USER_PROTOCOL_F_MQ feature flags.
Packets are routed to the appropriate RX queue based on which TX queue they
originated from, following the virtio specification's automatic receive
steering requirements.

This series adds:
- Multiqueue capability advertisement (VIRTIO_NET_F_MQ and
  VHOST_USER_PROTOCOL_F_MQ features)
- Per-queue-pair packet pools to support concurrent queue operations
- Queue pair parameter throughout the network stack, propagated through all
  protocol handlers (TCP, UDP, ICMP, ARP, DHCP, DHCPv6, NDP)
- Flow-aware queue routing that tracks the originating TX queue for each flow
  and routes return packets to the corresponding RX queue
- Test coverage with VHOST_USER_MQ environment variable to validate multiqueue
  functionality across all protocols (TCP, UDP, ICMP) and services (DHCP, NDP)

Current behavior:
- TX queue selection is controlled by the guest kernel's networking stack
- RX packets are routed to queues based on their associated flows, with the
  queue assignment updated on each packet from TX to maintain affinity
- Host-initiated flows (e.g., from socket-side connections) currently default
  to queue pair 0

The changes are transparent to single-queue operation - passt/pasta modes and
single-queue vhost-user configurations continue to work unchanged, always
using queue pair 0.

v3:
- Removed --max-qpairs configuration option - multiqueue support is now
  always enabled up to 16 queue pairs without requiring explicit configuration
- Replaced "tap: Add queue pair parameter throughout the packet processing
  path" with "tap: Convert packet pools to per-queue-pair arrays for
  multiqueue" - simplified implementation by converting global pools to arrays
  rather than passing pool parameters throughout
- Changed qpair parameter type from int to unsigned int throughout the codebase
- Simplified test infrastructure - queues parameter is always set on netdev,
  mq=true added to virtio-net only when VHOST_USER_MQ > 1
- Updated QEMU usage hints to always show multiqueue-capable command line

v2:
- New patch: "tap: Remove pool parameter from tap4_handler() and tap6_handler()"
  to clean up unused parameters before adding queue pair parameter
- Changed to one packet pool per queue pair instead of shared pools across
  all queue pairs
- Split "multiqueue: Add queue-aware flow management..." into two patches:
  - "tap: Add queue pair parameter throughout the packet processing path"
  - "flow: Add queue pair tracking to flow management"
- Updated test infrastructure patch with refined implementation

Laurent Vivier (6):
  tap: Remove pool parameter from tap4_handler() and tap6_handler()
  vhost-user: Enable multiqueue
  test: Add multiqueue support to vhost-user test infrastructure
  vhost-user: Add queue pair parameter throughout the network stack
  tap: Convert packet pools to per-queue-pair arrays for multiqueue
  flow: Add queue pair tracking to flow management

 arp.c          |  15 +++--
 arp.h          |   6 +-
 dhcp.c         |   5 +-
 dhcp.h         |   2 +-
 dhcpv6.c       |  12 ++--
 dhcpv6.h       |   2 +-
 flow.c         |  33 +++++++++
 flow.h         |  17 +++++
 fwd.c          |  18 ++---
 fwd.h          |   5 +-
 icmp.c         |  25 ++++---
 icmp.h         |   4 +-
 ndp.c          |  35 ++++++----
 ndp.h          |   7 +-
 netlink.c      |   2 +-
 tap.c          | 177 ++++++++++++++++++++++++++++---------------------
 tap.h          |  20 +++---
 tcp.c          |  47 +++++++------
 tcp.h          |   7 +-
 tcp_vu.c       |   8 ++-
 test/lib/setup |  21 +++---
 test/run       |  23 +++++++
 udp.c          |  47 +++++++------
 udp.h          |   6 +-
 udp_flow.c     |   8 ++-
 udp_flow.h     |   2 +-
 udp_internal.h |   4 +-
 udp_vu.c       |   4 +-
 vhost_user.c   |  10 +--
 virtio.h       |   2 +-
 vu_common.c    |  15 +++--
 vu_common.h    |   3 +-
 32 files changed, 374 insertions(+), 218 deletions(-)

-- 
2.51.1