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

[Jie Hai <haijie1@huawei.com>]

Hi, Ferruh

Kindly ping for reply.

Thanks,
Jie Hai
On 2024/3/8 19:36, Jie Hai wrote:
> On 2024/3/1 19:10, Ferruh Yigit wrote:
>> On 3/1/2024 6:55 AM, huangdengdui wrote:
>>>
>>>
>>> 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?
>>>
>>
>> If hns3 behaving against the documented behavior, I don't understand why
>> you are pushing for merging this patch, instead of fixing it.
>>
>>
>> Other drivers behavior is something else, not directly related to this
>> patch, but again if you can provide references we can discuss with their
>> maintainers.
>>
>>
>>>>
>>>>> 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?
>>
>> There is already API documentation about KEEP_CRC, I think that is
>> already sufficient for driver developers.
>>
>> I am just brainstorming if updating './doc/guides/nics/features.rst' can
>> help end user, but it is not an action or blocker for this patch.
>>
>> Next step is to update this path.
>>
> 
> 
> Hi, Ferruh,
> 
> Thanks for your attention.
> I have the following suggestions for the email discussion.
> Please take the time to see if they make sense.
> 
> For pkt_len and data_len, there is no clear document indicating
> whether the length should include the CRC.
> However, according to the usage of the driver and the APP, it
> is obvious that almost all drivers do not include the CRC by default.
> 
> The issue you raised about pkt_len/data_len supposedly containing CRC
> and users not being able to get CRC has been around for a long
> time, at least dating back to DPDK 18.11 when there was no hns3
> driver. And there is no clear solution to this problem for now.
> 
> This issue is not caused by the current patch and is not related
> to the problem to be solved by the current patch.
> Therefore, it is recommended that the problem corresponding to the current
> patch should be fixed first.
> 
> The problem that the pkt_len/data_len should contain the CRC
> and the user should access the CRC can be discussed later.
> 
> I have the following two options:
> 
> 1. Modify the corresponding document to specify that pkt_len/data_len
> should contain CRC, and modify all related drivers. This requires the
> participation and discussion of other driver developers.
> 
> 2. Users can use rte_pktmbuf_dump() to print packet data.
> The length of the packet data to be printed can be specified.
> However, the API restricts that the length of the data required is
> less than data_len. Therefore, users cannot obtain the CRC value.
> However, the result of the rte_pktmbuf_tailroom() API can tell how
> many bytes after data_len are accessible. Users can use 
> rte_pktmbuf_tailroom
> and keep_crc offload to obtain the CRC value of packets.
> 
>> .