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

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

On 4/4/2024 2:26 PM, Konstantin Ananyev wrote:
> 
> 
>>>> -----Original Message-----
>>>> From: Stephen Hemminger <stephen@networkplumber.org>
>>>> Sent: Tuesday, January 9, 2024 11:07 PM
>>>> To: Konstantin Ananyev <konstantin.ananyev@huawei.com>
>>>> Cc: dev@dpdk.org; arshdeep.kaur@intel.com; Gowda, Sandesh <sandesh.gowda@intel.com>; Reshma Pattan
>>>> <reshma.pattan@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@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?
> 
> Please see my comment above (I copied it here too):
>> Yes, in that way, one secondary would not be able to enable/disable pdump on another secondary, only on itself, but might be it is not needed?
> 

I saw it Konstantin, but it wasn't clear to me what you are suggesting,
that is why I am asking more.

Do you suggest when testpmd run as secondary process and doing
forwarding, it should do the tasks of pdump itself and we don't use
pdump at all?