Re: [PATCH net-next v2] samples/bpf: fixup some tools to be able to support xdp multibuffer

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

On 13/01/2023 23:07, Tariq Toukan wrote:
> 
> 
> On 10/01/2023 22:59, Maxim Mikityanskiy wrote:
>> On Tue, Jan 03, 2023 at 05:21:53PM -0800, Jakub Kicinski wrote:
>>> On Tue, 03 Jan 2023 16:19:49 +0100 Toke Høiland-Jørgensen wrote:
>>>> Hmm, good question! I don't think we've ever explicitly documented any
>>>> assumptions one way or the other. My own mental model has certainly
>>>> always assumed the first frag would continue to be the same size as in
>>>> non-multi-buf packets.
>>>
>>> Interesting! :) My mental model was closer to GRO by frags
>>> so the linear part would have no data, just headers.
>>>
>>> A random datapoint is that bpf_xdp_adjust_head() seems
>>> to enforce that there is at least ETH_HLEN.
>>
>> Also bpf_xdp_frags_increase_tail has the following check:
>>
>>     if (!rxq->frag_size || rxq->frag_size > xdp->frame_sz)
>>         return -EOPNOTSUPP;
>>
>> However, I can't seem to find where the `frag_size > frame_sz` part is
>> actually used. Maybe this condition can be dropped? Can someone shed
>> some light?
>>
>> BTW, Tariq, we seem to have missed setting frag_size to a non-zero
>> value.
> 
> Hey Maxim,
> Indeed. We use xdp_rxq_info_reg, it passes 0 as frag_size.
> 
>> Could you check that increasing the tail indeed doesn't work on
>> fragmented packets on mlx5e? I can send a oneliner to fix that.
> 
> I can test early next week, and update.

Hi Maxim,

Hacking the existing adjust_tail sample program, in between other high 
prio tasks, to make it work with frags took me some time.
But I can approve the fix below (or equivalent) is needed. Please go on 
and submit it.

Regards,
Tariq

--- a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
@@ -600,7 +600,7 @@ static int mlx5e_init_rxq_rq(struct mlx5e_channel 
*c, struct mlx5e_params *param
         if (err)
                 return err;

-       return xdp_rxq_info_reg(&rq->xdp_rxq, rq->netdev, rq->ix, 
c->napi.napi_id);
+       return __xdp_rxq_info_reg(&rq->xdp_rxq, rq->netdev, rq->ix, 
c->napi.napi_id, PAGE_SIZE);
  }

  static int mlx5_rq_shampo_alloc(struct mlx5_core_dev *mdev,