[dpdk-dev] doc: announce ABI change for mbuf structure

  For 16.11, the mbuf structure will be modified implying ABI breakage.
Some discussions already took place here:
http://www.dpdk.org/dev/patchwork/patch/12878/

Signed-off-by: Olivier Matz <olivier.matz@6wind.com>
---
 doc/guides/rel_notes/deprecation.rst | 6 ++++++
 1 file changed, 6 insertions(+)
  

On Tue, Jul 19, 2016 at 04:01:15PM +0200, Olivier Matz wrote:
> For 16.11, the mbuf structure will be modified implying ABI breakage.
> Some discussions already took place here:
> http://www.dpdk.org/dev/patchwork/patch/12878/
> 
> Signed-off-by: Olivier Matz <olivier.matz@6wind.com>
> ---
>  doc/guides/rel_notes/deprecation.rst | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/doc/guides/rel_notes/deprecation.rst b/doc/guides/rel_notes/deprecation.rst
> index f502f86..2245bc2 100644
> --- a/doc/guides/rel_notes/deprecation.rst
> +++ b/doc/guides/rel_notes/deprecation.rst
> @@ -41,3 +41,9 @@ Deprecation Notices
>  * The mempool functions for single/multi producer/consumer are deprecated and
>    will be removed in 16.11.
>    It is replaced by rte_mempool_generic_get/put functions.
> +
> +* ABI changes are planned for 16.11 in the ``rte_mbuf`` structure: some
> +  fields will be reordered to facilitate the writing of ``data_off``,
> +  ``refcnt``, and ``nb_segs`` in one operation. Indeed, some platforms
> +  have an overhead if the store address is not naturally aligned. The
> +  useless ``port`` field will also be removed at the same occasion.
> -- 

Have we fully bottomed out on the mbuf changes. I'm not sure that once patches
start getting considered for merge, new opinions may come forward. For instance,
is the "port" field really "useless"?

Would it not be better to put in a less specific deprecation notice? What happens
if this notice goes in and the final changes are different from those called out
here?

/Bruce
  

Hi Bruce,

On 07/19/2016 04:40 PM, Bruce Richardson wrote:
> On Tue, Jul 19, 2016 at 04:01:15PM +0200, Olivier Matz wrote:
>> For 16.11, the mbuf structure will be modified implying ABI breakage.
>> Some discussions already took place here:
>> http://www.dpdk.org/dev/patchwork/patch/12878/
>>
>> Signed-off-by: Olivier Matz <olivier.matz@6wind.com>
>> ---
>>  doc/guides/rel_notes/deprecation.rst | 6 ++++++
>>  1 file changed, 6 insertions(+)
>>
>> diff --git a/doc/guides/rel_notes/deprecation.rst b/doc/guides/rel_notes/deprecation.rst
>> index f502f86..2245bc2 100644
>> --- a/doc/guides/rel_notes/deprecation.rst
>> +++ b/doc/guides/rel_notes/deprecation.rst
>> @@ -41,3 +41,9 @@ Deprecation Notices
>>  * The mempool functions for single/multi producer/consumer are deprecated and
>>    will be removed in 16.11.
>>    It is replaced by rte_mempool_generic_get/put functions.
>> +
>> +* ABI changes are planned for 16.11 in the ``rte_mbuf`` structure: some
>> +  fields will be reordered to facilitate the writing of ``data_off``,
>> +  ``refcnt``, and ``nb_segs`` in one operation. Indeed, some platforms
>> +  have an overhead if the store address is not naturally aligned. The
>> +  useless ``port`` field will also be removed at the same occasion.
>> -- 
> 
> Have we fully bottomed out on the mbuf changes. I'm not sure that once patches
> start getting considered for merge, new opinions may come forward. For instance,
> is the "port" field really "useless"?
> 
> Would it not be better to put in a less specific deprecation notice? What happens
> if this notice goes in and the final changes are different from those called out
> here?

Yes, you are right. What about the following text?

ABI changes are planned for 16.11 in the ``rte_mbuf`` structure: some
fields may be reordered to facilitate the writing of ``data_off``,
``refcnt``, and ``nb_segs`` in one operation. Indeed, some platforms
have an overhead if the store address is not naturally aligned. The
``port`` field may also be removed at the same occasion.


Thanks,
Olivier
  

> -----Original Message-----
> From: Olivier Matz [mailto:olivier.matz@6wind.com]
> Sent: Tuesday, July 19, 2016 4:04 PM
> To: Richardson, Bruce <bruce.richardson@intel.com>
> Cc: dev@dpdk.org; jerin.jacob@caviumnetworks.com;
> thomas.monjalon@6wind.com
> Subject: Re: [dpdk-dev] [PATCH] doc: announce ABI change for mbuf
> structure
> 
> Hi Bruce,
> 
> On 07/19/2016 04:40 PM, Bruce Richardson wrote:
> > On Tue, Jul 19, 2016 at 04:01:15PM +0200, Olivier Matz wrote:
> >> For 16.11, the mbuf structure will be modified implying ABI breakage.
> >> Some discussions already took place here:
> >> http://www.dpdk.org/dev/patchwork/patch/12878/
> >>
> >> Signed-off-by: Olivier Matz <olivier.matz@6wind.com>
> >> ---
> >>  doc/guides/rel_notes/deprecation.rst | 6 ++++++
> >>  1 file changed, 6 insertions(+)
> >>
> >> diff --git a/doc/guides/rel_notes/deprecation.rst
> >> b/doc/guides/rel_notes/deprecation.rst
> >> index f502f86..2245bc2 100644
> >> --- a/doc/guides/rel_notes/deprecation.rst
> >> +++ b/doc/guides/rel_notes/deprecation.rst
> >> @@ -41,3 +41,9 @@ Deprecation Notices
> >>  * The mempool functions for single/multi producer/consumer are
> deprecated and
> >>    will be removed in 16.11.
> >>    It is replaced by rte_mempool_generic_get/put functions.
> >> +
> >> +* ABI changes are planned for 16.11 in the ``rte_mbuf`` structure:
> >> +some
> >> +  fields will be reordered to facilitate the writing of
> >> +``data_off``,
> >> +  ``refcnt``, and ``nb_segs`` in one operation. Indeed, some
> >> +platforms
> >> +  have an overhead if the store address is not naturally aligned.
> >> +The
> >> +  useless ``port`` field will also be removed at the same occasion.
> >> --
> >
> > Have we fully bottomed out on the mbuf changes. I'm not sure that once
> > patches start getting considered for merge, new opinions may come
> > forward. For instance, is the "port" field really "useless"?
> >
> > Would it not be better to put in a less specific deprecation notice?
> > What happens if this notice goes in and the final changes are
> > different from those called out here?
> 
> Yes, you are right. What about the following text?
> 
> ABI changes are planned for 16.11 in the ``rte_mbuf`` structure: some
> fields may be reordered to facilitate the writing of ``data_off``,
> ``refcnt``, and ``nb_segs`` in one operation. Indeed, some platforms have
> an overhead if the store address is not naturally aligned. The ``port``
> field may also be removed at the same occasion.
> 
Better. Two suggestions:
1. change "Indeed" to "because" and join the sentences.
2. change the last sentence to be even more general: "Other mbuf fields, such as the port field, may be moved or removed as part of this mbuf work".

/Bruce
  

On 07/19/2016 05:07 PM, Richardson, Bruce wrote:
> 
> 
>> -----Original Message-----
>> From: Olivier Matz [mailto:olivier.matz@6wind.com]
>> Sent: Tuesday, July 19, 2016 4:04 PM
>> To: Richardson, Bruce <bruce.richardson@intel.com>
>> Cc: dev@dpdk.org; jerin.jacob@caviumnetworks.com;
>> thomas.monjalon@6wind.com
>> Subject: Re: [dpdk-dev] [PATCH] doc: announce ABI change for mbuf
>> structure
>>
>> Hi Bruce,
>>
>> On 07/19/2016 04:40 PM, Bruce Richardson wrote:
>>> On Tue, Jul 19, 2016 at 04:01:15PM +0200, Olivier Matz wrote:
>>>> For 16.11, the mbuf structure will be modified implying ABI breakage.
>>>> Some discussions already took place here:
>>>> http://www.dpdk.org/dev/patchwork/patch/12878/
>>>>
>>>> Signed-off-by: Olivier Matz <olivier.matz@6wind.com>
>>>> ---
>>>>  doc/guides/rel_notes/deprecation.rst | 6 ++++++
>>>>  1 file changed, 6 insertions(+)
>>>>
>>>> diff --git a/doc/guides/rel_notes/deprecation.rst
>>>> b/doc/guides/rel_notes/deprecation.rst
>>>> index f502f86..2245bc2 100644
>>>> --- a/doc/guides/rel_notes/deprecation.rst
>>>> +++ b/doc/guides/rel_notes/deprecation.rst
>>>> @@ -41,3 +41,9 @@ Deprecation Notices
>>>>  * The mempool functions for single/multi producer/consumer are
>> deprecated and
>>>>    will be removed in 16.11.
>>>>    It is replaced by rte_mempool_generic_get/put functions.
>>>> +
>>>> +* ABI changes are planned for 16.11 in the ``rte_mbuf`` structure:
>>>> +some
>>>> +  fields will be reordered to facilitate the writing of
>>>> +``data_off``,
>>>> +  ``refcnt``, and ``nb_segs`` in one operation. Indeed, some
>>>> +platforms
>>>> +  have an overhead if the store address is not naturally aligned.
>>>> +The
>>>> +  useless ``port`` field will also be removed at the same occasion.
>>>> --
>>>
>>> Have we fully bottomed out on the mbuf changes. I'm not sure that once
>>> patches start getting considered for merge, new opinions may come
>>> forward. For instance, is the "port" field really "useless"?
>>>
>>> Would it not be better to put in a less specific deprecation notice?
>>> What happens if this notice goes in and the final changes are
>>> different from those called out here?
>>
>> Yes, you are right. What about the following text?
>>
>> ABI changes are planned for 16.11 in the ``rte_mbuf`` structure: some
>> fields may be reordered to facilitate the writing of ``data_off``,
>> ``refcnt``, and ``nb_segs`` in one operation. Indeed, some platforms have
>> an overhead if the store address is not naturally aligned. The ``port``
>> field may also be removed at the same occasion.
>>
> Better. Two suggestions:
> 1. change "Indeed" to "because" and join the sentences.
> 2. change the last sentence to be even more general: "Other mbuf fields, such as the port field, may be moved or removed as part of this mbuf work".

It's much better indeed ;)
Thanks Bruce, I'll submit a v2.