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

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Message-ID: <6ab07d63-10c7-c591-152b-473ebf37b5ff@gmail.com>
Date:   Wed, 25 Jan 2023 14:49:56 +0200
From:   Tariq Toukan <ttoukan.linux@...il.com>
To:     Maxim Mikityanskiy <maxtram95@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Eelco Chaudron <echaudro@...hat.com>,
        Tariq Toukan <tariqt@...dia.com>
Cc:     Toke Høiland-Jørgensen <toke@...hat.com>,
        Andy Gospodarek <andrew.gospodarek@...adcom.com>,
        ast@...nel.org, daniel@...earbox.net, davem@...emloft.net,
        hawk@...nel.org, john.fastabend@...il.com, andrii@...nel.org,
        kafai@...com, songliubraving@...com, yhs@...com,
        kpsingh@...nel.org, lorenzo.bianconi@...hat.com,
        netdev@...r.kernel.org, bpf@...r.kernel.org,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Andy Gospodarek <gospo@...adcom.com>,
        Lorenzo Bianconi <lorenzo@...nel.org>, gal@...dia.com,
        Saeed Mahameed <saeedm@...dia.com>
Subject: Re: [PATCH net-next v2] samples/bpf: fixup some tools to be able to
 support xdp multibuffer



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,