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

[huangdengdui <huangdengdui@huawei.com>]

On 2024/2/29 17:25, Ferruh Yigit wrote:
> On 2/29/2024 3:58 AM, huangdengdui wrote:
>>
>>
>> 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.
>>
> 
> I think it is clear that pkt_len and data_len should contain crc_len, we
> can ask for more comments.
This patch doesn't change the logic for hns3 PMD and the implementation of
other PMDs supported KEEP_CRC is like hns3 PMD. Can we merge this patch first?

> 
>> 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.
>>
> 
> Not for drivers, just a suggestion that if we should update feature
> documentation with above information for users. So there is no
> dependency to features document update.
> 
> 
Sorry I'm more confused. What should we do next?