Issues around packet capture when secondary process is doing rx/tx

[Ferruh Yigit]

On 1/10/2024 8:11 PM, Konstantin Ananyev wrote:
> 
> 
>> -----Original Message-----
>> From: Stephen Hemminger <stephen at networkplumber.org>
>> Sent: Tuesday, January 9, 2024 11:07 PM
>> To: Konstantin Ananyev <konstantin.ananyev at huawei.com>
>> Cc: dev at dpdk.org; arshdeep.kaur at intel.com; Gowda, Sandesh <sandesh.gowda at intel.com>; Reshma Pattan
>> <reshma.pattan at intel.com>
>> Subject: Re: Issues around packet capture when secondary process is doing rx/tx
>>
>> On Mon, 8 Jan 2024 15:13:25 +0000
>> Konstantin Ananyev <konstantin.ananyev at huawei.com> wrote:
>>
>>>> I have been looking at a problem reported by Sandesh
>>>> where packet capture does not work if rx/tx burst is done in secondary process.
>>>>
>>>> The root cause is that existing rx/tx callback model just doesn't work
>>>> unless the process doing the rx/tx burst calls is the same one that
>>>> registered the callbacks.
>>>>
>>>> An example sequence would be:
>>>> 	1. dumpcap (or pdump) as secondary tells pdump in primary to register callback
>>>> 	2. secondary process calls rx_burst.
>>>> 	3. rx_burst sees the callback but it has pointer pdump_rx which is not necessarily
>>>> 	   at same location in primary and secondary process.
>>>> 	4. indirect function call in secondary to bad location likely causes crash.
>>>
>>> As I remember, RX/TX callbacks were never intended to work over multiple processes.
>>> Right now RX/TX callbacks are private for the process, different process simply should not
>>> see/execute them.
>>> I.E. it callbacks list is part of 'struct rte_eth_dev' itself, not the rte_eth_dev.data that is shared
>>> between processes.
>>> It should be normal, wehn for the same port/queue you will end-up with different list of callbacks
>>> for different processes.
>>> So, unless I am missing something, I don't see how we can end-up with 3) and 4) from above:
>>> From my understanding secondary process will never see/call primary's callbacks.
>>>
>>> About pdump itself, it was a while when I looked at it last time, but as I remember to start it to work,
>>> server process has to call rte_pdump_init() which in terns register PDUMP_MP handler.
>>> I suppose for the secondary process to act as a 'pdump server' it needs to call rte_pdump_init() itself,
>>> though I am not sure such option is supported right now.
>>>
>>
>> Did some more tests with modified testpmd, and reached some conclusions:
>>
>> The logical interface would be to allow rte_pdump_init() to be called by
>>    the process that would be using rx/tx burst API's.
>>
>>   This doesn't work as it should because the multi-process socket API
>>   assumes that the it only runs the server in primary.  The secondary
>>   can start its own MP thread, but it won't work:
>>
>>   Primary EAL: Multi-process socket /var/run/dpdk/rte/mp_socket
>>   Secondary: EAL: Multi-process socket /var/run/dpdk/rte/mp_socket_6057_1ccd4157fd5
>>
>>   The problem is when client (pdump or dumpcap) tries to run, it uses the mp_socket
>>   in the primary which causes: EAL: Cannot find action: mp_pdump
>>
>>   Looks like the whole MP socket mechanism is just not up to this.
>>
>> Maybe pdump needs to have its own socket and control thread?
>> Or MP socket needs to have some multicast fanout to all secondaries?
> 
> Might be we can do something simpler: pass to pdump_enable(), where we want to enable it:
> on primary (remote_ process or secondary (local) process?
> And then for primary send a message over MP socket (as we doing now), and for secondary (itself)
> just do actual pdump enablement on it's own (install callbacks, etc.).
> Yes, in that way, one secondary would not be able to enable/idable pdump on another secondary,
> only on itself, but might be it is not needed?
> 
> 

How secondary, lets say testpmd secondary, install callbacks without
getting 'mp' & 'ring' info from pdump secondary process?