27/05/2020 09:31, Jerin Jacob: > On Wed, May 27, 2020 at 12:39 PM Olivier Matz <olivier.m...@6wind.com> wrote: > > On Tue, May 26, 2020 at 09:59:45PM +0530, Jerin Jacob wrote: > > > On Tue, May 26, 2020 at 9:36 PM Olivier Matz <olivier.m...@6wind.com> > > > wrote: > > > > On Tue, May 26, 2020 at 01:09:37PM +0530, Jerin Jacob wrote: > > > > > On Tue, May 26, 2020 at 2:54 AM Thomas Monjalon <tho...@monjalon.net> > > > > > wrote: > > > > > > > > > > > > Since dynamic fields and flags were added in 19.11, > > > > > > the idea was to use them for new features, not only PMD-specific. > > > > > > > > > > > > The rule is made more explicit in doxygen, in the mbuf guide, > > > > > > and in the contribution design guidelines. > > > > > > > > > > > > For more information about the original design, see the presentation > > > > > > https://www.dpdk.org/wp-content/uploads/sites/35/2019/10/DynamicMbuf.pdf > > > > > > > > > > > > Signed-off-by: Thomas Monjalon <tho...@monjalon.net> > > > > > > --- > > > > > > doc/guides/contributing/design.rst | 13 +++++++++++++ > > > > > > doc/guides/prog_guide/mbuf_lib.rst | 23 +++++++++++++++++++++++ > > > > > > lib/librte_mbuf/rte_mbuf_core.h | 2 ++ > > > > > > 3 files changed, 38 insertions(+) > > > > > > > > > > > > diff --git a/doc/guides/contributing/design.rst > > > > > > b/doc/guides/contributing/design.rst > > > > > > index d3dd694b65..508115d5bd 100644 > > > > > > --- a/doc/guides/contributing/design.rst > > > > > > +++ b/doc/guides/contributing/design.rst > > > > > > +Mbuf features > > > > > > +------------- > > > > > > + > > > > > > +The ``rte_mbuf`` structure must be kept small (128 bytes). > > > > > > + > > > > > > +In order to add new features without wasting buffer space for > > > > > > unused features, > > > > > > +some fields and flags can be registered dynamically in a shared > > > > > > area. > > > > > > > > > > I think, instead of "can", it should be "must" > > > > > > > > > > > +The "dynamic" mbuf area is the default choice for the new features. > > > > > > > > In my opinion, Thomas' proposal is correct, with the next sentence > > > > saying it is the default choice for new features. > > > > > > > > Giving guidelines is a good thing (thanks Thomas for documenting it), > > > > but I don't think we should be too strict: the door remains open for > > > > technical debate and exceptions. > > > > > > If you are open for the exception then it must be mention in what case > > > the exception is allowed and what are the criteria of the exception? > > > > > > For example, Why did n't we choose the following patch as expectation > > > http://patches.dpdk.org/patch/68733/ even if only one bit used. > > > > > > If we are not not defining the criteria, IMO, This patch serve no purpose > > > than > > > the existing situation. > > > > > > Do you think, any case where the dynamic scheme can not be used as a > > > replacement > > > for static other than performance hit. > > > > I don't think it is possible to anticipate all criteria in the > > documentation. With Thomas' proposal, it gives a direction is and a > > global view, but it must not completly replace reflection and > > discussion. > > I don't think, we need to anticipate all the criteria in the documentation. > At least ONE should be given as an example of an exception.
I think it is too early to be more specific in the guidelines. Do we agree this patch is a first good step in the documentation? We can extend the guidelines a bit later after having some discussions on specific cases, and probably in the techboard too. > I would say, > a) If a feature takes only one bit and its part of normative API spec > and it used in fastpath we should consider the static scheme. > b) Adding an exception to the existing list needs approval at least > from three maintainers > > For me, it is a very legitimate case to have support for > http://patches.dpdk.org/patch/68733/ to the static scheme > as it takes 1 bit for a feature and it is part of the normative spec. > I don't get in explanation in the ml, why > we can not make it as the static scheme for this case. We can continue discussion about this specific case in the right thread. Note: I don't have a definitive opinion on it, I need to read it carefully. > My worry is, if we are keeping as open-ended means, we are giving room > for the disparity among the vendors/feature > as I dont think, There is use case where dynamic scheme can not be > used as a replacement > for static other than performance hit.(Could think of any use case?) > So open ended boils down to preference to specific feature/vendor. I > think,that path should be avoided. Of course all rules and decisions have to be fair. It's not even a question.
