Re: [dpdk-dev] [PATCH] doc: add deprecation notice on timer lib cleanup

[Ray Kinsella <mdr@ashroe.eu>]

On 09/05/2019 10:38, Thomas Monjalon wrote:
> 09/05/2019 11:37, Burakov, Anatoly:
>> On 09-May-19 10:06 AM, Bruce Richardson wrote:
>>> On Thu, May 09, 2019 at 09:33:32AM +0100, Burakov, Anatoly wrote:
>>>> On 09-May-19 8:05 AM, David Marchand wrote:
>>>>> On Thu, May 9, 2019 at 3:11 AM Stephen Hemminger
>>>>> <stephen@networkplumber.org <mailto:stephen@networkplumber.org>> wrote:
>>>>>
>>>>>      On Wed,  8 May 2019 17:48:06 -0500
>>>>>      Erik Gabriel Carrillo <erik.g.carrillo@intel.com
>>>>>      <mailto:erik.g.carrillo@intel.com>> wrote:
>>>>>
>>>>>       > Due to an upcoming fix to allow the timer library to safely free its
>>>>>       > allocations during the finalize() call[1], an ABI change will be
>>>>>       > required. A new lock will be added to the rte_mem_config structure,
>>>>>       > which will be used by the timer library to synchronize init/finalize
>>>>>       > calls among multiple processes.
>>>>>       >
>>>>>       > [1] http://patches.dpdk.org/patch/53334/
>>>>>       >
>>>>>       > Signed-off-by: Erik Gabriel Carrillo <erik.g.carrillo@intel.com
>>>>>      <mailto:erik.g.carrillo@intel.com>>
>>>>>       > ---
>>>>>       >  doc/guides/rel_notes/deprecation.rst | 4 ++++
>>>>>       >  1 file changed, 4 insertions(+)
>>>>>       >
>>>>>       > diff --git a/doc/guides/rel_notes/deprecation.rst
>>>>>      b/doc/guides/rel_notes/deprecation.rst
>>>>>       > index b47c8c2..7551383 100644
>>>>>       > --- a/doc/guides/rel_notes/deprecation.rst
>>>>>       > +++ b/doc/guides/rel_notes/deprecation.rst
>>>>>       > @@ -31,6 +31,10 @@ Deprecation Notices
>>>>>       >
>>>>>       >      + ``rte_eal_devargs_type_count``
>>>>>       >
>>>>>       > +* eal: the ``rte_mem_config`` struct will change to include a
>>>>>      new lock that
>>>>>       > +  will allow the timer subsystem to safely release its
>>>>>      allocations at cleanup
>>>>>       > +  time. This will result in an ABI break.
>>>>>       > +
>>>>>       >  * vfio: removal of ``rte_vfio_dma_map`` and
>>>>>      ``rte_vfio_dma_unmap`` APIs which
>>>>>       >    have been replaced with ``rte_dev_dma_map`` and
>>>>>      ``rte_dev_dma_unmap``
>>>>>       >    functions.  The due date for the removal targets DPDK 20.02.
>>>>>
>>>>>      NAK
>>>>>
>>>>>      Please go to the effort of making rte_mem_config not part of the
>>>>>      visible ABI.
>>>>>      Then change it.
>>>>>
>>>>>
>>>>> +1.
>>>>
>>>> I agree on principle, however this won't solve the issue. It doesn't need to
>>>> be externally visible, but that's not all of its problems - it's also shared
>>>> between processes so there's an ABI contract between primary and secondary
>>>> too. This means that, even if the structure itself is not public, any
>>>> changes to it will still result in an ABI break. That's the nature of our
>>>> shared memory.
>>>>
>>>> In other words, if your goal is to avoid ABI breaks on changing this
>>>> structure, making it internal won't help in the slightest.
>>>>
>>>
>>> Is there an ABI contract between primary and secondary. I always assumed
>>> that if using secondary processes the requirement (though undocumented) was
>>> that both had to be linked against the exact same versions of DPDK?
>>>
>>
>> The fact that it's undocumented means we can't assume everyone will do 
>> that :)
>>
>> If the community agrees that primary/secondary processes should always 
>> use the same DPDK version (regardless of static/dynamic builds etc.), 
>> then this problem would probably be solved.
> 
> +1 to document that primary/secondary with different DPDK versions
> is not supported.
> 

+1,

but I think we need to go farther - we need a secondary process to check
with the primary process.
We can't assume everyone will read the documentation.