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

[huangdengdui <huangdengdui@huawei.com>]

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?