Hi Oliver > -----Original Message----- > From: Olivier MATZ [mailto:olivier.matz at 6wind.com] > Sent: Wednesday, June 10, 2015 10:33 PM > To: O'Driscoll, Tim; Zhang, Helin; dev at dpdk.org > Cc: Thomas Monjalon > Subject: Re: [dpdk-dev] [PATCH v6 01/18] mbuf: redefine packet_type in > rte_mbuf > > Hi Tim, Helin, > > On 06/02/2015 03:27 PM, O'Driscoll, Tim wrote: > > > >> -----Original Message----- > >> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Olivier MATZ > >> Sent: Monday, June 1, 2015 9:15 AM > >> To: Zhang, Helin; dev at dpdk.org > >> Subject: Re: [dpdk-dev] [PATCH v6 01/18] mbuf: redefine packet_type > >> in rte_mbuf > >> > >> Hi Helin, > >> > >> +CC Neil > >> > >> On 06/01/2015 09:33 AM, Helin Zhang wrote: > >>> In order to unify the packet type, the field of 'packet_type' in > >>> 'struct rte_mbuf' needs to be extended from 16 to 32 bits. > >>> Accordingly, some fields in 'struct rte_mbuf' are re-organized to > >>> support this change for Vector PMD. As 'struct rte_kni_mbuf' for KNI > >>> should be right mapped to 'struct rte_mbuf', it should be modified > >>> accordingly. In addition, Vector PMD of ixgbe is disabled by > >>> default, as 'struct rte_mbuf' changed. > >>> To avoid breaking ABI compatibility, all the changes would be > >>> enabled by RTE_UNIFIED_PKT_TYPE, which is disabled by default. > >> > >> What are the plans for this compile-time option in the future? > >> > >> I wonder what are the benefits of having this option in terms of ABI > >> compatibility: when it is disabled, it is ABI-compatible but the > >> packet-type feature is not present, and when it is enabled we have > >> the feature but it breaks the compatibility. > >> > >> In my opinion, the v5 is preferable: for this kind of features, I > >> don't see how the ABI can be preserved, and I think packet-type won't > >> be the only feature that will modify the mbuf structure. I think the > >> process described here should be applied: > >> http://dpdk.org/browse/dpdk/tree/doc/guides/rel_notes/abi.rst > >> > >> (starting from "Some ABI changes may be too significant to reasonably > >> maintain multiple versions of"). > >> > >> > >> Regards, > >> Olivier > >> > > > > This is just like the change that Steve (Cunming) Liang submitted for > > Interrupt > Mode. We have the same problem in both cases: we want to find a way to get > the features included, but need to comply with our ABI policy. So, in both > cases, > the proposal is to add a config option to enable the change by default, so we > maintain backward compatibility. Users that want these changes, and are > willing > to accept the associated ABI change, have to specifically enable them. > > > > We can note in the Deprecation Notices in the Release Notes for 2.1 that > > these > config options will be removed in 2.2. The features will then be enabled by > default. > > > > This seems like a good compromise which allows us to get these changes into > 2.1 but avoids breaking the ABI policy. > > Sorry for the late answer. > > After some thoughts on this topic, I understand that having a compile-time > option is perhaps a good compromise between keeping compatibility and having > new features earlier. > > I'm just afraid about having one #ifdef in the code for each new feature that > cannot keep the ABI compatibility. > What do you think about having one option -- let's call it > "CONFIG_RTE_NEXT_ABI" --, that is disabled by default, and that would surround > any new feature that breaks the ABI? Will we allow this type of workaround for a long time? If yes, agree with your good idea.
Regards, Helin > > This would have several advantages: > - only 2 cases (on or off), the combinatorial is smaller than > having one option per feature > - all next features breaking the abi can be identified by a grep > - the code inside the #ifdef can be enabled in a simple operation > by Thomas after each release. > > Thomas, any comment? > > Regards, > Olivier >
