[PATCH v5 00/12] 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)
- 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
- Epoll fd derived directly from queue pair, removing the separate epollid
  field and adding flow_migrate() for moving flows between queue pairs
- 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.

v5:
- Rebase
- Dropped "tap: Convert packet pools to per-queue-pair arrays for multiqueue"
- Split "vhost-user: Add queue pair parameter throughout the network stack"
  into separate per-protocol patches (tap, arp, tcp, udp, dhcp/dhcpv6,
  icmp, ndp) for easier review
- New patch: "flow: Derive epoll fd from queue pair, removing epollid field"
  derives epoll fd directly from queue pair, removing the redundant epollid
  field and adding flow_migrate()/FLOW_MIGRATE() for existing flows
- tcp_keepalive() and tcp_inactivity() now filter flows by queue pair
- Renamed "vhost-user: Enable multiqueue" to "vhost-user: Advertise
  multiqueue support"

v4:
- Rebase
- Added QPAIR_DEFAULT, QPAIR_FROMGUEST_QUEUE(), QPAIR_TOGUEST_QUEUE(), and
  QPAIR_FROM_QUEUE() macros to centralize queue pair calculations
- Replaced hardcoded 0 with QPAIR_DEFAULT throughout for clarity
- Set queue pair at flow creation time in icmp_ping_new() and udp_flow_new()
  rather than after creation
- Removed vhost-user-specific queue macros (VHOST_USER_TX_QUEUE,
  VHOST_USER_IS_QUEUE_TX, VHOST_USER_IS_QUEUE_RX) in favor of generic
  QPAIR_* macros for better consistency

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 (12):
  tap: Remove pool parameter from tap4_handler() and tap6_handler()
  vhost-user: Advertise multiqueue support
  test: Add multiqueue support to vhost-user test infrastructure
  tap: Thread queue pair through all remaining tap paths
  arp: Pass queue pair explicitly through ARP send path
  tcp: Pass queue pair explicitly through TCP send path
  udp: Pass queue pair explicitly through UDP send path
  dhcp/dhcpv6: Pass queue pair explicitly through DHCP send path
  icmp: Pass queue pair explicitly through ICMP send path
  ndp: Pass queue pair explicitly through NDP send path
  flow: Add queue pair tracking to flow management
  flow: Derive epoll fd from queue pair, removing epollid field

 arp.c          |  15 +--
 arp.h          |   6 +-
 dhcp.c         |   5 +-
 dhcp.h         |   2 +-
 dhcpv6.c       |  12 ++-
 dhcpv6.h       |   2 +-
 flow.c         |  66 ++++++++-----
 flow.h         |  28 ++++--
 fwd.c          |   4 +-
 icmp.c         |  29 ++++--
 icmp.h         |   7 +-
 ndp.c          |  40 ++++----
 ndp.h          |   7 +-
 passt.c        |  27 +++---
 passt.h        |   8 ++
 tap.c          | 134 ++++++++++++++------------
 tap.h          |  21 +++--
 tcp.c          | 249 ++++++++++++++++++++++++++++++-------------------
 tcp.h          |  15 +--
 tcp_buf.c      |  10 +-
 tcp_internal.h |   7 +-
 tcp_splice.c   |   2 +-
 tcp_vu.c       |  22 +++--
 tcp_vu.h       |   6 +-
 test/lib/setup |  21 +++--
 test/run       |  23 +++++
 udp.c          |  45 +++++----
 udp.h          |   9 +-
 udp_flow.c     |  27 +++---
 udp_flow.h     |   4 +-
 udp_internal.h |   3 +-
 udp_vu.c       |   6 +-
 udp_vu.h       |   3 +-
 vhost_user.c   |  14 ++-
 vhost_user.h   |   9 --
 virtio.h       |   2 +-
 vu_common.c    |  22 +++--
 vu_common.h    |   3 +-
 38 files changed, 557 insertions(+), 358 deletions(-)

-- 
2.54.0