Re: [PATCH 0/4] vhost-user: Add multiqueue support

[David Gibson <david@gibson.dropbear.id.au>]

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On Fri, Nov 07, 2025 at 03:38:57PM +0100, Laurent Vivier wrote:
> This series implements multiqueue support for vhost-user mode, allowing passt
> to utilize multiple queue pairs. There is no improved network performance because
> we keep using only one thread.
> 
> The implementation introduces a --max-queues parameter to configure up to 16
> queue pairs (32 virtqueues) in vhost-user mode. Packets are routed to the
> appropriate RX queue based on which TX queue they originated from, enabling the
> guest kernel to distribute network traffic across multiple queues
> and vCPUs.

I find this description a little bit confusing, since at the packet
(L2) level things going to an Rx queue don't really have an
originating Tx queue.  I assume you mean that each flow gets
associated to a single queue pair, so both Rx and Tx packets on that
flow will use the same queue pair (and, later, thread).  Is that
correct?  If so I think it would be clearer to explicitly describe
this in terms of flows.

> This series adds:
> - configuration support for multiqueue via --max-queues parameter
> - queue parameter threading throughout the network stack - a significant
>   refactoring that propagates queue information through all protocol handlers
>   (TCP, UDP, ICMP, ARP, DHCP, DHCPv6, NDP)
> - flow-aware queue routing that matches RX queue selection to the incoming
>   TX queue, maintaining proper packet affinity
> - comprehensive test coverage with VHOST_USER_MQ environment variable to
>   validate multiqueue functionality across all test scenarios
> 
> Current behavior: TX queue selection is controlled by the guest kernel, while
> RX packets are routed to queues based on their associated flows. Host-initiated
> flows currently default to queue 0.
> 
> The RX queue of a flow is updated on each new packet from the TX queue to
> maintain affinity.
> 
> The changes maintain backward compatibility - without --max-queues, behavior
> remains unchanged with single-queue operation.
> 
> Laurent Vivier (4):
>   vhost-user: Enable multiqueue
>   vhost-user: Add queue parameter throughout the network stack
>   multiqueue: Add queue-aware flow management for multiqueue support
>   test: Add multiqueue support to vhost-user test infrastructure
> 
>  arp.c          |  12 ++---
>  arp.h          |   4 +-
>  conf.c         |  31 ++++++++++++-
>  dhcp.c         |   5 ++-
>  dhcp.h         |   2 +-
>  dhcpv6.c       |  12 ++---
>  dhcpv6.h       |   2 +-
>  flow.c         |  32 +++++++++++++
>  flow.h         |  10 +++++
>  fwd.c          |   4 +-
>  icmp.c         |  25 ++++++-----
>  icmp.h         |   2 +-
>  ndp.c          |  32 +++++++------
>  ndp.h          |   5 ++-
>  passt.h        |   2 +
>  tap.c          | 120 +++++++++++++++++++++++++++++--------------------
>  tap.h          |  18 ++++----
>  tcp.c          |  82 ++++++++++++++++++---------------
>  tcp.h          |  11 ++---
>  tcp_vu.c       |   8 ++--
>  test/lib/setup |  60 +++++++++++++++++++------
>  test/run       |  23 ++++++++++
>  udp.c          |  40 ++++++++++-------
>  udp.h          |  12 ++---
>  udp_flow.c     |   8 +++-
>  udp_flow.h     |   2 +-
>  udp_vu.c       |   4 +-
>  vhost_user.c   |  38 +++++++++-------
>  virtio.h       |   2 +-
>  vu_common.c    |  13 +++---
>  vu_common.h    |   3 +-
>  31 files changed, 416 insertions(+), 208 deletions(-)
> 
> -- 
> 2.51.0
> 
> 

-- 
David Gibson (he or they)	| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you, not the other way
				| around.
http://www.ozlabs.org/~dgibson

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