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

[Ferruh Yigit <ferruh.yigit@amd.com>]

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.

> 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.