Re: [PATCH] net/mlx5: store rxq MTU at allocation time

[Dariusz Sosnowski <dsosnowski@nvidia.com>]

Hi,

Thank you very much for your contribution.

Code looks good to me. Please see a small comment below.

On Tue, Oct 28, 2025 at 11:01:44AM +0100, a.schollmeyer@syseleven.de wrote:
> From: Adrian Schollmeyer <a.schollmeyer@syseleven.de>
> 
> For shared Rx queues, equal MTU for all ports sharing queues is enforced
> using mlx5_shared_rxq_match() to make sure, the memory allocated in the
> Rx buffer is large enough. The check uses the MTU as reported by the
> ports' private dev_data structs, which contain the MTU currently set for
> the device. In case one port's MTU is altered after Rx queues are
> allocated and then a second port joins the shared Rx queue with the old,
> yet correct MTU, the check fails despite the fact that the Rx buffer
> size is correct for both ports.
> 
> This patch adds a new entry to the Rx queue control structure that
> captures the MTU at the time the Rx buffer was allocated, since this is
> the relevant information that needs to be checked when a port joins a
> shared Rx queue.
> 
> Fixes: 09c2555303be ("net/mlx5: support shared Rx queue")

The offending patch was part of 21.11,
so this fix is a candidate for backporting to previously released LTS versions.

Could you send a v2 patch with "Cc: stable@dpdk.org" added after "Fixes" tag?

When sending this change, could you also please send the patch directly to mlx5 maintainers as well?
There's a script in DPDK repository which would add relevant people
based on the changed files - devtools/get-maintainer.sh
It's usage is described in here: https://doc.dpdk.org/guides/contributing/patches.html#sending-patches

> 
> Signed-off-by: Adrian Schollmeyer <a.schollmeyer@syseleven.de>
> ---
>  drivers/net/mlx5/mlx5_rx.h  | 1 +
>  drivers/net/mlx5/mlx5_rxq.c | 6 +++++-
>  2 files changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/mlx5/mlx5_rx.h b/drivers/net/mlx5/mlx5_rx.h
> index 6380895502..58bc2c9f21 100644
> --- a/drivers/net/mlx5/mlx5_rx.h
> +++ b/drivers/net/mlx5/mlx5_rx.h
> @@ -169,6 +169,7 @@ struct __rte_cache_aligned mlx5_rxq_data {
>  /* RX queue control descriptor. */
>  struct mlx5_rxq_ctrl {
>  	struct mlx5_rxq_data rxq; /* Data path structure. */
> +	uint16_t mtu; /* Original MTU that the queue was allocated with. */
>  	LIST_ENTRY(mlx5_rxq_ctrl) next; /* Pointer to the next element. */
>  	LIST_HEAD(priv, mlx5_rxq_priv) owners; /* Owner rxq list. */
>  	struct mlx5_rxq_obj *obj; /* Verbs/DevX elements. */
> diff --git a/drivers/net/mlx5/mlx5_rxq.c b/drivers/net/mlx5/mlx5_rxq.c
> index 5cf7d4971b..c652204ea8 100644
> --- a/drivers/net/mlx5/mlx5_rxq.c
> +++ b/drivers/net/mlx5/mlx5_rxq.c
> @@ -773,7 +773,7 @@ mlx5_shared_rxq_match(struct mlx5_rxq_ctrl *rxq_ctrl, struct rte_eth_dev *dev,
>  			dev->data->port_id, idx);
>  		return false;
>  	}
> -	if (priv->mtu != spriv->mtu) {
> +	if (priv->mtu != rxq_ctrl->mtu) {
>  		DRV_LOG(ERR, "port %u queue index %u failed to join shared group: mtu mismatch",
>  			dev->data->port_id, idx);
>  		return false;
> @@ -1799,6 +1799,10 @@ mlx5_rxq_new(struct rte_eth_dev *dev, uint16_t idx, uint16_t desc,
>  	}
>  	LIST_INIT(&tmpl->owners);
>  	MLX5_ASSERT(n_seg && n_seg <= MLX5_MAX_RXQ_NSEG);
> +	/*
> +	 * Save the original MTU to check against for shared rx queues.
> +	 */
> +	tmpl->mtu = dev->data->mtu;
>  	/*
>  	 * Save the original segment configuration in the shared queue
>  	 * descriptor for the later check on the sibling queue creation.
> -- 
> 2.34.1
> 

Best regards,
Dariusz Sosnowski