[dpdk-stable] [dpdk-dev] [PATCH] net/af_xdp: fix support of secondary process

[Ferruh Yigit]

On 9/23/2021 1:33 PM, Loftus, Ciara wrote:
>>>>>>
>>>>>> Doing basic operations like info_get or get_stats was broken
>>>>>> in af_xdp PMD. The info_get would crash because dev->device
>>>>>> was NULL in secondary process. Fix this by doing same initialization
>>>>>> as af_packet and tap devices.
>>>>>>
>>>>>> The get_stats would crash because the XDP socket is not open in
>>>>>> primary process. As a workaround don't query kernel for dropped
>>>>>> packets when called from secondary process.
>>>>>>
>>>>>> Note: this does not address the other bug which is that transmitting
>>>>>> in secondary process is broken because the send() in tx_kick
>>>>>> will fail because XDP socket fd is not valid in secondary process.
>>>>>
>>>>> Hi Stephen,
>>>>>
>>>>> Apologies for the delayed reply, I was on vacation.
>>>>>
>>>>> In the Bugzilla report you suggest we:
>>>>> "mark AF_XDP as broken in with primary/secondary
>>>>> and return an error in probe in secondary process".
>>>>> I agree with this suggestion. However with this patch we still permit
>>>> secondary, and just make sure it doesn't crash for get_stats. Did you
>> change
>>>> your mind?
>>>>> Personally, I would prefer to have primary/secondary either working
>> 100%
>>>> or else not allowed at all by throwing an error during probe. What do you
>>>> think? Do you have a reason/use case to permit secondary processes
>> despite
>>>> some features not being available eg. full stats, tx?
>>>>>
>>>>> Thanks,
>>>>> Ciara
>>>>
>>>> There are two cases where secondary is useful even if send/receive can't
>>>> work from secondary process.
>>>> The pdump and proc-info applications can work with these patches.
>>>>
>>>> I am using XDP over pdump as an easy way to get packets into the code
>> for
>>>> testing.
>>>>
>>>> The flag in the documentation doesn't have a "limited" version.
>>>> If you want, will send another patch to disable secondary support.
>>>
>>> Thanks for explaining. Since there are use cases for secondary, even if the
>> functionality is limited, I don't think it should be disabled.
>>> Since we can't flag it as 'limited' in the feature matrix, could you please add
>> a note about the send/receive limitation in the AF_XDP PMD documentation
>> in a v2? There are already a number of limitations listed, which you can add
>> to.
>>>
>>> Thanks,
>>> Ciara
>>>
>>>>
>>>> Supporting secondary, means adding a mechanism to pass the socket
>>>> around.
>>
>> Looking at this in more detail, and my recommendation is:
>> For 21.11 release (and mark it as Fixes so it gets backported). Have the driver
>> return -ENOTSUP in secondary process.
>>
>> For 22.03 add real secondary support using the rte_mp_msg to pass
>> necessary
>> state to secondary process. Includes socket (and other memory regions?).
>>
>> The pdump and proc-info cases are only useful for developer testing, and
>> there are
>> other ways to do the same thing.
> 
> 
> +1 that sounds reasonable to me.
> 

This patch superseded by following which disables the secondary process support:
https://patches.dpdk.org/project/dpdk/patch/20210930134604.32585-1-ciara.loftus@intel.com/