Re: [PATCH net-next V9 12/14] net/mlx5: qos: Support cross-device tx scheduling

[Jakub Kicinski <kuba@kernel.org>]

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---
net/mlx5: qos: Support cross-device tx scheduling

This commit relaxes the restriction that rate groups can only contain vports
from the same E-Switch. It enables cross-device TX scheduling if the hardware
supports it, LAG is enabled, and the E-Switches share a devlink device.

> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/esw/qos.c b/drivers/net/ethernet/mellanox/mlx5/core/esw/qos.c
> --- a/drivers/net/ethernet/mellanox/mlx5/core/esw/qos.c
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/esw/qos.c

[ ... ]

> @@ -1738,18 +1761,44 @@ int mlx5_esw_devlink_rate_node_del(struct devlink_rate *rate_node, void *priv,
>  	return 0;
>  }
>  
> +static int
> +mlx5_esw_validate_cross_esw_scheduling(struct mlx5_eswitch *esw,
> +				       struct mlx5_esw_sched_node *parent,
> +				       struct netlink_ext_ack *extack)
> +{

[ ... ]

> +	if (!mlx5_lag_is_active(esw->dev)) {
> +		NL_SET_ERR_MSG_MOD(extack,
> +				   "Cross E-Switch scheduling requires LAG to be activated");
> +		return -EOPNOTSUPP;
> +	}

What happens to the cross-device rate scheduling if LAG is deactivated
after the configuration is applied?

When LAG is deactivated, the LAG state is torn down in hardware, but there
does not appear to be a corresponding cleanup or update triggered for the
cross-eswitch QoS scheduling elements.

Could this result in a regression where the hardware TSAR tree and devlink
rate configuration remain pointing to a now-invalid VHCA association,
bypassing the state validation and causing traffic drops or firmware errors?

> +
> +	return 0;
> +}