Re: [PATCH net-next 5/5] net/mlx5e: do not create xdp_redirect for non-uplink rep

[Tariq Toukan <ttoukan.linux@gmail.com>]

On 01/11/2024 15:22, Daniel Machon wrote:
> Hi Tariq, William
> 
>> From: William Tu <witu@nvidia.com>
>>
>> XDP and XDP socket require extra SQ/RQ/CQs. Most of these resources
>> are dynamically created: no XDP program loaded, no resources are
>> created. One exception is the SQ/CQ created for XDP_REDRIECT, used
>> for other netdev to forward packet to mlx5 for transmit. The patch
>> disables creation of SQ and CQ used for egress XDP_REDIRECT, by
>> checking whether ndo_xdp_xmit is set or not.
>>
>> For netdev without XDP support such as non-uplink representor, this
>> saves around 0.35MB of memory, per representor netdevice per channel.
>>
>> Signed-off-by: William Tu <witu@nvidia.com>
>> Reviewed-by: Parav Pandit <parav@nvidia.com>
>> Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
>> ---
>>   .../net/ethernet/mellanox/mlx5/core/en_main.c   | 17 +++++++++++------
>>   1 file changed, 11 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
>> index 2f609b92d29b..59d7a0e28f24 100644
>> --- a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
>> +++ b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
>> @@ -2514,6 +2514,7 @@ static int mlx5e_open_queues(struct mlx5e_channel *c,
>>                               struct mlx5e_params *params,
>>                               struct mlx5e_channel_param *cparam)
>>   {
>> +       const struct net_device_ops *netdev_ops = c->netdev->netdev_ops;
>>          struct dim_cq_moder icocq_moder = {0, 0};
>>          struct mlx5e_create_cq_param ccp;
>>          int err;
>> @@ -2534,10 +2535,12 @@ static int mlx5e_open_queues(struct mlx5e_channel *c,
>>          if (err)
>>                  goto err_close_icosq_cq;
>>
>> -       c->xdpsq = mlx5e_open_xdpredirect_sq(c, params, cparam, &ccp);
>> -       if (IS_ERR(c->xdpsq)) {
>> -               err = PTR_ERR(c->xdpsq);
>> -               goto err_close_tx_cqs;
>> +       if (netdev_ops->ndo_xdp_xmit) {
> 
> Is it possible to have ndo_xdp_xmit() set, but *not* have an XDP prog attached
> to the netdevice? I see that c->xdp = !!params->xdp_prog - could that be
> used instead?
> 
> /Daniel
> 

Hi Daniel,

Unlike drivers of other vendors, in mlx5e we have the 
egress-xdp-redirect feature enabled without the need to load a dummy xdp 
program in rx.