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

["Burakov, Anatoly" <anatoly.burakov@intel.com>]

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.

-- 
Thanks,
Anatoly