From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thomas Monjalon Subject: Re: [dpdk-announce] important design choices - statistics - ABI Date: Fri, 19 Jun 2015 15:16:53 +0200 Message-ID: <1784476.c2eg9hZKIA@xps13> References: <9092314.MoyqUJ5VU2@xps13> <2237584.tmRa3ku4eh@xps13> <20150619130255.GA4619@hmsreliant.think-freely.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7Bit Cc: dev@dpdk.org To: Neil Horman Return-path: Received: from mail-wg0-f53.google.com (mail-wg0-f53.google.com [74.125.82.53]) by dpdk.org (Postfix) with ESMTP id A05D9C808 for ; Fri, 19 Jun 2015 15:17:56 +0200 (CEST) Received: by wguu7 with SMTP id u7so17306500wgu.3 for ; Fri, 19 Jun 2015 06:17:56 -0700 (PDT) In-Reply-To: <20150619130255.GA4619@hmsreliant.think-freely.org> List-Id: patches and discussions about DPDK List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" 2015-06-19 09:02, Neil Horman: > On Fri, Jun 19, 2015 at 02:32:33PM +0200, Thomas Monjalon wrote: > > 2015-06-19 06:26, Neil Horman: > > > On Thu, Jun 18, 2015 at 04:55:45PM +0000, O'Driscoll, Tim wrote: > > > > For the 2.1 release, I think we should agree to make patches that change > > > > the ABI controllable via a compile-time option. I like Olivier's proposal > > > > on using a single option (CONFIG_RTE_NEXT_ABI) to control all of these > > > > changes instead of a separate option per patch set (see > > > > http://dpdk.org/ml/archives/dev/2015-June/019147.html), so I think we > > > > should rework the affected patch sets to use that approach for 2.1. > > > > > > This is a bad idea. Making ABI dependent on compile time options isn't a > > > maintainable solution. It breaks the notion of how LIBABIVER is supposed to > > > work (that is to say you make it impossible to really tell what ABI version you > > > are building). > > > > The idea was to make LIBABIVER increment dependent of CONFIG_RTE_NEXT_ABI. > > So one ABI version number refers always to the same ABI. > > > > > If you have two compile time options that modify the ABI, you > > > have to burn through 4 possible LIBABIVER version values to accomodate all > > > possible combinations, and then you need to remember that when you make them > > > statically applicable. > > > > The idea is to have only 1 compile-time option: CONFIG_RTE_NEXT_ABI. > > > > Your intent when introducing ABI policy was to allow smooth porting of > > applications from a DPDK version to another. Right? > > The adopted solution was to provide backward compatibility during 1 release. > > But there are cases where it's not possible. So the policy was to notice > > the future change and wait one release cycle to break the ABI (failing > > compatibility goals). > > The compile-time option may provide an alternative DPDK packaging when the > > ABI backward compatibility cannot be provided (case of mbuf changes). > > In such case, it's still possible to upgrade DPDK by providing 2 versions of > > DPDK libs. So the existing apps continue to link with the previous ABI and > > have the possibility of migrating to the new one. > > Another advantage of this approach is that we don't have to wait 1 release > > to integrate the changes. > > The last advantage is to benefit early of these changes with static libraries. > > Hm, ok, thats a bit more reasonable, but it still seems shaky to me. > Implementing an ABI preview option like this implies the notion that, after a > release, you have to remove all the ifdefs that you inserted to create the new > ABI. That seems like an easy task, but it becomes a pain when the ABI delta is > large, and is predicated on the centralization of work effort (that is to say > you need to identify someone to submit the 'remove the NEXT_ABI config ifdefs > from the build' patch every release. It won't be so huge if we reserve the NEXT_ABI solution to changes which cannot have easy backward compatibility with the compat macros you introduced. I feel I can do the job of removing the ifdefs NEXT_ABI after each release. At the same time, the deprecated API, using the compat macros, will be removed. > What might be better would be a dpdk-next branch (or even a dpdk-next tree, of > the sort that Thomas Herbert proposed a few weeks ago). This tree was created after Thomas' request: http://dpdk.org/browse/next/dpdk-next/ > Patches that aren't ABI stable can be put on the next-branch/tree in thier > final format. You can delcare the branch unstable (thereby reserving your > right to rebase it). People can use that to preview the next ABI version > (complete with the update LIBABIVER bump), and when you release dpdk-X, > the new ABI for dpdk-X+1 is achieved by simply merging. Having this tree living would be a nice improvement but it won't provide any stable (and enough validated) releases to rely on.