Re: [PATCH v6 02/12] vhost-user: Advertise multiqueue support

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

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On Fri, Jul 31, 2026 at 06:16:07PM +0200, Laurent Vivier wrote:
> Allow the guest to negotiate multiple virtqueue pairs by advertising
> VIRTIO_NET_F_MQ and VHOST_USER_PROTOCOL_F_MQ feature flags, and
> increase VHOST_USER_MAX_VQS from 2 to 32, supporting up to 16 queue
> pairs.
> 
> Replace the VHOST_USER_RX_QUEUE, VHOST_USER_TX_QUEUE,
> VHOST_USER_IS_QUEUE_TX(), and VHOST_USER_IS_QUEUE_RX() macros with a
> general set of QPAIR_* macros in passt.h that translate between queue
> pair numbers and virtqueue indices.  These are needed now that queue
> indices are no longer limited to 0 and 1.
> 
> Add a queue pair parameter to vu_send_single(), propagating it to the
> virtqueue selection.  All callers currently pass QPAIR_DEFAULT (0):
> only the first RX queue is used for receiving.  The guest kernel
> selects which TX queue to use for transmission.  Full multi-RX-queue
> load balancing will be implemented separately.
> 
> Signed-off-by: Laurent Vivier <lvivier@redhat.com>

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

[snip]
>  /**
> - * vu_send_single() - Send a buffer to the front-end using the RX virtqueue
> - * @c:		execution context
> + * vu_send_single() - Send a buffer to the front-end using a specified virtqueue
> + * @c:		Execution context
> + * @qpair:	Queue pair on which to send the buffer
>   * @buf:	address of the buffer
>   * @size:	size of the buffer
>   *
>   * Return: number of bytes sent, -1 if there is an error
>   */
> -int vu_send_single(const struct ctx *c, const void *buf, size_t size)
> +int vu_send_single(const struct ctx *c, unsigned int qpair, const void *buf, size_t size)
>  {
>  	struct vu_dev *vdev = c->vdev;
> -	struct vu_virtq *vq = &vdev->vq[VHOST_USER_RX_QUEUE];
>  	struct vu_virtq_element elem[VIRTQUEUE_MAX_SIZE];
>  	struct iovec in_sg[VIRTQUEUE_MAX_SIZE];
> +	struct vu_virtq *vq;

Nit: belongs one line lower down...

>  	size_t total, in_total;
>  	int elem_cnt;
>  	int i;
>  
> +	vq = &vdev->vq[QPAIR_TOGUEST_QUEUE(qpair)];
> +

... or you could put this expression in the initialiser and it
wouldn't move at all.


>  	trace("vu_send_single size %zu", size);
>  
>  	if (!vu_queue_enabled(vq) || !vu_queue_started(vq)) {
> diff --git a/vu_common.h b/vu_common.h
> index 817384175a1d..f5603d9ddeb6 100644
> --- a/vu_common.h
> +++ b/vu_common.h
> @@ -23,7 +23,8 @@ void vu_flush(const struct vu_dev *vdev, struct vu_virtq *vq,
>  	      struct vu_virtq_element *elem, int elem_cnt, size_t frame_len);
>  void vu_kick_cb(struct vu_dev *vdev, union epoll_ref ref,
>  		const struct timespec *now);
> -int vu_send_single(const struct ctx *c, const void *buf, size_t size);
> +int vu_send_single(const struct ctx *c, unsigned int qpair, const void *buf,
> +		   size_t size);
>  void vu_pad(const struct iovec *iov, size_t cnt, size_t frame_len);
>  
>  #endif /* VU_COMMON_H */
> -- 
> 2.54.0
> 

-- 
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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