[dpdk-dev] [dpdk-announce] important design choices - statistics - ABI

[Zhang, Helin]

Hi Neil

> -----Original Message-----
> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Neil Horman
> Sent: Wednesday, June 17, 2015 6:35 PM
> To: Thomas Monjalon
> Cc: announce at dpdk.org
> Subject: Re: [dpdk-dev] [dpdk-announce] important design choices - statistics -
> ABI
> 
> On Wed, Jun 17, 2015 at 01:29:47AM +0200, Thomas Monjalon wrote:
> > Hi all,
> >
> > Sometimes there are some important discussions about architecture or
> > design which require opinions from several developers. Unfortunately,
> > we cannot read every threads. Maybe that using the announce mailing
> > list will help to bring more audience to these discussions.
> > Please note that
> > 	- the announce@ ML is moderated to keep a low traffic,
> > 	- every announce email is forwarded to dev@ ML.
> > In case you want to reply to this email, please use dev at dpdk.org address.
> >
> > There were some debates about software statistics disabling.
> > Should they be always on or possibly disabled when compiled?
> > We need to take a decision shortly and discuss (or agree) this proposal:
> > 	http://dpdk.org/ml/archives/dev/2015-June/019461.html
> >
> > During the development of the release 2.0, there was an agreement to
> > keep ABI compatibility or to bring new ABI while keeping old one during one
> release.
> > In case it's not possible to have this transition, the (exceptional)
> > break should be acknowledged by several developers.
> > 	http://dpdk.org/doc/guides-2.0/rel_notes/abi.html
> > There were some interesting discussions but not a lot of participants:
> >
> > http://thread.gmane.org/gmane.comp.networking.dpdk.devel/8367/focus=84
> > 61
> >
> > During the current development cycle for the release 2.1, the ABI
> > question arises many times in different threads.
> > To add the hash key size field, it is proposed to use a struct padding gap:
> > 	http://dpdk.org/ml/archives/dev/2015-June/019386.html
> > To support the flow director for VF, there is no proposal yet:
> > 	http://dpdk.org/ml/archives/dev/2015-June/019343.html
> > To add the speed capability, it is proposed to break ABI in the release 2.2:
> > 	http://dpdk.org/ml/archives/dev/2015-June/019225.html
> > To support vhost-user multiqueues, it is proposed to break ABI in 2.2:
> > 	http://dpdk.org/ml/archives/dev/2015-June/019443.html
> > To add the interrupt mode, it is proposed to add a build-time option
> > CONFIG_RTE_EAL_RX_INTR to switch between compatible and ABI breaking
> binary:
> > 	http://dpdk.org/ml/archives/dev/2015-June/018947.html
> > To add the packet type, there is a proposal to add a build-time option
> > CONFIG_RTE_NEXT_ABI common to every ABI breaking features:
> > 	http://dpdk.org/ml/archives/dev/2015-June/019172.html
> > We must also better document how to remove a deprecated ABI:
> > 	http://dpdk.org/ml/archives/dev/2015-June/019465.html
> > The ABI compatibility is a new constraint and we need to better
> > understand what it means and how to proceed. Even the macros are not yet
> well documented:
> > 	http://dpdk.org/ml/archives/dev/2015-June/019357.html
> >
> > Thanks for your attention and your participation in these important choices.
> >
> 
> Thomas-
> 	Just to re-iterate what you said earlier, and what was discussed in the
> previous ABI discussions
> 
> 1) ABI stability was introduced to promote DPDK's ability to be included with
> various linux and BSD distributions.  Distributions, by and large, favor building
> libraries as DSO's, favoring security and updatability in favor of all out
> performance.
> 
> 2) The desire was to put DPDK developers in a mindset whereby ABI stability was
> something they needed to think about during development, as the DPDK
> exposes many data structures and instances that cannot be changed without
> breaking ABI
> 
> 3) The versioning mechanism was introduced to allow for backward compatibility
> during periods in which we needed to support both an old an new ABI
> 
> 4) As Stephan and others point out, its not expected that we will always be able
> to maintain ABI, and as such an easy library versioning mechanism was
> introduced to prevent the loading of an incompatible library with an older
> application
> 
> 5) The ABI policy was introduced to create a method by which new ABI facets
> could be scheduled while allowing distros to prepare their downstream users for
> the upcomming changes.
> 
> 
> It seems to me, looking back over these last few months, that we're falling down
> a bit on our use of (3).  I've seen several people take advantage of the ABI
> scheduled updates, but no one has tried the versioning interface, and as a result
> patches are getting delayed, which was never my intent.  Not sure whats to be
> done about that, but we should probably address it.  Is use of the versionnig
> interface just too hard or convoluted?
That means we should try to use versioning mechanism as more as possible?
Are there any rules/instructions to judge what type of changes we should try
versioning mechanism, and what else we shouldn't try?
Is there any good examples of using versioning mechanism for reference?
Even not in DPDK project.

Thanks,
Helin


> 
> Neil