Re: [PATCH] net/hns3: fix Rx packet truncation when KEEP CRC enabled

[huangdengdui <huangdengdui@huawei.com>]

On 2024/2/28 21:07, Ferruh Yigit wrote:
> On 2/28/2024 2:27 AM, huangdengdui wrote:
>>
>>
>> On 2024/2/27 0:43, Ferruh Yigit wrote:
>>> On 2/26/2024 3:16 AM, Jie Hai wrote:
>>>> On 2024/2/23 21:53, Ferruh Yigit wrote:
>>>>> On 2/20/2024 3:58 AM, Jie Hai wrote:
>>>>>> Hi, Ferruh,
>>>>>>
>>>>>> Thanks for your review.
>>>>>>
>>>>>> On 2024/2/7 22:15, Ferruh Yigit wrote:
>>>>>>> On 2/6/2024 1:10 AM, Jie Hai wrote:
>>>>>>>> From: Dengdui Huang <huangdengdui@huawei.com>
>>>>>>>>
>>>>>>>> When KEEP_CRC offload is enabled, some packets will be truncated and
>>>>>>>> the CRC is still be stripped in following cases:
>>>>>>>> 1. For HIP08 hardware, the packet type is TCP and the length
>>>>>>>>      is less than or equal to 60B.
>>>>>>>> 2. For other hardwares, the packet type is IP and the length
>>>>>>>>      is less than or equal to 60B.
>>>>>>>>
>>>>>>>
>>>>>>> If a device doesn't support the offload by some packets, it can be
>>>>>>> option to disable offload for that device, instead of calculating it in
>>>>>>> software and append it.
>>>>>>
>>>>>> The KEEP CRC feature of hns3 is faulty only in the specific packet
>>>>>> type and small packet(<60B) case.
>>>>>> What's more, the small ethernet packet is not common.
>>>>>>
>>>>>>> Unless you have a specific usecase, or requirement to support the
>>>>>>> offload.
>>>>>>
>>>>>> Yes, some users of hns3 are already using this feature.
>>>>>> So we cannot drop this offload
>>>>>>
>>>>>>> <...>
>>>>>>>
>>>>>>>> @@ -2492,10 +2544,16 @@ hns3_recv_pkts_simple(void *rx_queue,
>>>>>>>>                goto pkt_err;
>>>>>>>>              rxm->packet_type = hns3_rx_calc_ptype(rxq, l234_info,
>>>>>>>> ol_info);
>>>>>>>> -
>>>>>>>>            if (rxm->packet_type == RTE_PTYPE_L2_ETHER_TIMESYNC)
>>>>>>>>                rxm->ol_flags |= RTE_MBUF_F_RX_IEEE1588_PTP;
>>>>>>>>    +        if (unlikely(rxq->crc_len > 0)) {
>>>>>>>> +            if (hns3_need_recalculate_crc(rxq, rxm))
>>>>>>>> +                hns3_recalculate_crc(rxq, rxm);
>>>>>>>> +            rxm->pkt_len -= rxq->crc_len;
>>>>>>>> +            rxm->data_len -= rxq->crc_len;
>>>>>>>>
>>>>>>>
>>>>>>> Removing 'crc_len' from 'mbuf->pkt_len' & 'mbuf->data_len' is
>>>>>>> practically same as stripping CRC.
>>>>>>>
>>>>>>> We don't count CRC length in the statistics, but it should be
>>>>>>> accessible
>>>>>>> in the payload by the user.
>>>>>> Our drivers are behaving exactly as you say.
>>>>>>
>>>>>
>>>>> If so I missed why mbuf 'pkt_len' and 'data_len' reduced by
>>>>> 'rxq->crc_len', can you please explain what above lines does?
>>>>>
>>>>>
>>>> @@ -2470,8 +2523,7 @@ hns3_recv_pkts_simple(void *rx_queue,
>>>>          rxdp->rx.bd_base_info = 0;
>>>>
>>>>          rxm->data_off = RTE_PKTMBUF_HEADROOM;
>>>> -        rxm->pkt_len = (uint16_t)(rte_le_to_cpu_16(rxd.rx.pkt_len)) -
>>>> -                rxq->crc_len;
>>>> +        rxm->pkt_len = rte_le_to_cpu_16(rxd.rx.pkt_len);
>>>>
>>>> In the previous code above, the 'pkt_len' is set to the length obtained
>>>> from the BD. the length obtained from the BD already contains CRC length.
>>>> But as you said above, the DPDK requires that the length of the mbuf
>>>> does not contain CRC length . So we subtract 'rxq->crc_len' from
>>>> mbuf'pkt_len' and 'data_len'. This patch doesn't change the logic, it
>>>> just moves the code around.
>>>>
>>>
>>> Nope, I am not saying mbuf length shouldn't contain CRC length, indeed
>>> it is other way around and this is our confusion.
>>>
>>> CRC length shouldn't be in the statistics, I mean in received bytes stats.
>>> Assume that received packet is 128 bytes and we know it has the CRC,
>>> Rx received bytes stat should be 124 (rx_bytes = 128 - CRC = 124)
>>>
>>> But mbuf->data_len & mbuf->pkt_len should have full frame length,
>>> including CRC.
>>>
>>> As application explicitly requested to KEEP CRC, it will know last 4
>>> bytes are CRC.
>>> Anything after 'mbuf->data_len' in the mbuf buffer is not valid, so if
>>> you reduce 'mbuf->data_len' by CRC size, application can't know if 4
>>> bytes after 'mbuf->data_len' is valid CRC or not.
>>>
>> I agree with you.
>>
>> But the implementation of other PMDs supported KEEP_CRC is like this.
>> In addition, there are probably many users that are already using it.
>> If we modify it, it may cause applications incompatible.
>>
>> what do you think?
>>
> This is documented in the ethdev [1], better to follow the documentation
> for all PMDs, can you please highlight the relevant driver code, we can
> discuss it with their maintainers.
> 
> Alternatively we can document this additionally in the KEEP_CRC feature
> document if it helps for the applications.
> 
> 
> [1]
> https://git.dpdk.org/dpdk/tree/lib/ethdev/rte_ethdev.h?h=v23.11#n257

Currently，this documentation does not describe whether pkt_len and data_len should contain crc_len.

Do you mean that we add this description in the KEEP_CRC feature document
and notify all drivers that support KEEP_CRC to follow this documentation?

If so, can you merge this patch first?
Then we send a RFC to disscuss it with all PMDs maintainer.