Re: [dpdk-dev] [PATCH v4 1/4] ethdev: add tm support for shaper config in pkt mode

["Dumitrescu, Cristian" <cristian.dumitrescu@intel.com>]

> -----Original Message-----
> From: Thomas Monjalon <thomas@monjalon.net>
> Sent: Tuesday, April 28, 2020 4:54 PM
> To: Jerin Jacob <jerinjacobk@gmail.com>; Dumitrescu, Cristian
> <cristian.dumitrescu@intel.com>
> Cc: Richardson, Bruce <bruce.richardson@intel.com>; Yigit, Ferruh
> <ferruh.yigit@intel.com>; Luca Boccassi <bluca@debian.org>; Nithin
> Dabilpuram <nithind1988@gmail.com>; Singh, Jasvinder
> <jasvinder.singh@intel.com>; Andrew Rybchenko
> <arybchenko@solarflare.com>; dev@dpdk.org; jerinj@marvell.com;
> kkanas@marvell.com; Nithin Dabilpuram <ndabilpuram@marvell.com>;
> Kinsella, Ray <ray.kinsella@intel.com>; Neil Horman
> <nhorman@tuxdriver.com>; Kevin Traynor <ktraynor@redhat.com>; David
> Marchand <david.marchand@redhat.com>
> Subject: Re: [dpdk-dev] [PATCH v4 1/4] ethdev: add tm support for shaper
> config in pkt mode
> 
> 28/04/2020 17:04, Luca Boccassi:
> > On Tue, 2020-04-28 at 15:45 +0100, Bruce Richardson wrote:
> > > On Tue, Apr 28, 2020 at 03:06:20PM +0100, Ferruh Yigit wrote:
> > > > On 4/27/2020 5:59 PM, Jerin Jacob wrote:
> > > > > On Mon, Apr 27, 2020 at 10:19 PM Ferruh Yigit
> <ferruh.yigit@intel.com> wrote:
> > > > > > On 4/27/2020 5:29 PM, Jerin Jacob wrote:
> > > > > > > On Mon, Apr 27, 2020 at 9:42 PM Ferruh Yigit
> <ferruh.yigit@intel.com> wrote:
> > > > > > > > On 4/27/2020 10:19 AM, Dumitrescu, Cristian wrote:
> > > > > > > > > From: Yigit, Ferruh <ferruh.yigit@intel.com>
> > > > > > > > > > On 4/24/2020 11:28 AM, Dumitrescu, Cristian wrote:
> > > > > > > > > > > From: Nithin Dabilpuram <nithind1988@gmail.com>
> > > > > > > > > > > > This patch also updates tm port/level/node capability
> structures with
> > > > > > > > > > > > exiting features of scheduler wfq packet mode,
> scheduler wfq byte mode
> > > > > > > > > > > > and private/shared shaper byte mode.
> > > > > > > > > > > >
> > > > > > > > > > > > SoftNIC PMD is also updated with new capabilities.
> [...]
> > > > > > > > > > Hi Nithin,
> > > > > > > > > >
> > > > > > > > > > It looks like patch is causing ABI break, I am getting following
> warning [1],
> > > > > > > > > > can you please check?
> > > > > > > > > >
> > > > > > > > > > [1]
> > > > > > > > > > https://pastebin.com/XYNFg14u
> > > > > > > > >
> > > > > > > > > Hi Ferruh,
> > > > > > > > >
> > > > > > > > > The RTE_TM API is marked as experimental,
> > > > > > > > > but it looks that this was not correctly marked
> > > > > > > > > when __rte_experimental ABI checker was introduced.
> > > > > > > > >
> > > > > > > > > It is marked as experimental at the top of the rte_tm.h,
> > > > > > > > > similarly to other APIs introduced around same time,
> > > > > > > > > but it was not correctly picked up by the ABI check procedure
> > > > > > > > > when later introduced, so __rte_experimental was not added
> to every function.
> > > > > > > > >
> > > > > > > >
> > > > > > > > :(
> > > > > > > >
> > > > > > > > Is it time to mature them?
> > > > > > > >
> > > > > > > > As you said they are not marked as experimental both in header
> file (function
> > > > > > > > declarations) and .map file.
> > > > > > > >
> > > > > > > > The problem is, they are not marked as experimental in
> DPDK_20.0 ABI (v19.11),
> > > > > > > > so marking them as experimental now will break the ABI. Not
> sure what to do,
> > > > > > > > cc'ed a few ABI related names for comment.
> > > > > > > >
> > > > > > > > For me, we need to proceed as the experimental tag removed
> and APIs become
> > > > > > > > mature starting from v19.11, since this is what happened in
> practice, and remove
> > > > > > > > a few existing being experimental references in the doxygen
> comments.
> > > > > > >
> > > > > > > I think, accidentally we can not make a library as NON-
> experimental.
> > > > > > > TM never went through experimental to mature transition(see git
> log
> > > > > > > lib/librte_ethdev/rte_tm.h)
> > > > > > > It was a bug to not mark as experimental in each function in the
> ABI process.
> > > > > > > Some of the features like packet marking are not even
> implemented by any HW.
> > > > > > > I think, we can make API stable only all the features are
> implemented
> > > > > > > by one or two HW.
> 
> Yes this is what was decided one or two years ago I think.
> But rte_tm API was introduced 3 years ago and is implemented by 6 PMDs.
> 
> 
> 
> > > > > > Fair enough, specially if the API is not ready yet.
> > > > > >
> > > > > > But they were part of stable ABI, and marking them as experimental
> now will
> > > > > > break the old applications using these APIs.
> > > > >
> > > > > it is still marked as EXPERIMENTAL everywhere and API is not ready
> yet.
> 
> rte_tm is implemented in 6 PMDs.
> 
> 
> > > > Existing experimental marks are text only for human parsing.
> > > >
> > > > The compiler attribute and build time checks are missing, and the
> symbol in the
> > > > binary doesn't have experimental tag. Our scripts and automated
> checks won't
> > > > detect it as experimental.
> > > >
> > > > My point is just having experimental comment in header file is not
> enough to
> > > > qualify the APIs as experimental.
> > > >
> > > > > Anyway, we need to break the ABI to make it work on various HW.
> 
> Yes this is why I was asking in 19.11 to check our API,
> in order to avoid such situation.
> 
> 
> > > > > I am not sure what to do?
> 
> Either manage ABI versioning, or wait 20.11.
> 
> 
> > > > > IMO, We need to send a patch as Fixes: for the bug of not adding
> > > > > __rte_experimental in each function.
> 
> No, this is wrong.
> 

Why exactly is this wrong? This is the gap that caused the current discussion, right?

> 
> > > > Yes, this is where we are, both you and Cristian suggest API is not ready
> and
> > > > should be experimental, but they were part of stable ABI, making them
> > > > experimental will break the ABI.
> > > > It looks like there is no good option but we should select one of the bad
> ones.
> > > >
> > > > > Traffic Management API - EXPERIMENTAL
> > > > > M: Cristian Dumitrescu <cristian.dumitrescu@intel.com>
> > > > > T: git://dpdk.org/next/dpdk-next-qos
> > > > > F: lib/librte_ethdev/rte_tm*
> > > > > > > > Ray, Neil, David, Luca, Kevin, what do you think?
> > > While I'm not called any of those names, allow me to give my 2c.
> > >
> > > Since these are marked in binaries as part of the stable ABI, I think we
> > > need to honour that for the next two releases 20.05 and 20.08 [which
> means
> > > that we need to put in versioned functions for any changes, not that we
> > > can't change anything]
> > >
> > > For 20.11, I think these should then have one of two options taken:
> > > * have these "fixed" and ready to be marked as stable, and officially part
> > >   of v21 ABI or
> > > * mark them as experimental properly, and look to have them as part of
> the
> > >   v22 or subsequent ABI
> > >
> > > Given the comments here, I would tend towards the latter of the above
> two
> > > options, but that's really a decision for the maintainers.
> > >
> > > Remember, this is not the first bug we have encountered where we
> messed up
> > > some ABI versions in the 19.11 release, and, like the previous one with
> the
> > > screwed up version number, I think we need to honour the ABI
> committments
> > > made, especially since in this case it's only for a few more months till
> > > 20.11 development starts.
> > >
> > > /Bruce
> >
> > +1
> >
> > If they are not ready now, they haven't been ready for the past 6
> > months either, so staying not ready for 6 more is the lesser evil.
> 
> This API is almost 3 years old (release 17.08).
> That's good to improve it but we must respect the ABI contract that
> we all agreed.
> 
> 
> Summary:
> 17.08: rte_tm is introduced.
> 17.11: rte_mtr is introduced as experimental, but rte_tm remains stable.
> 18.02: __rte_experimental tag is introduced (including for rte_mtr),
> but rte_tm remains untouched as it is in stable ABI.
> 19.11: stable ABI is frozen until 20.11
> 20.05: rte_tm improvement is blocked because of ABI breakage.
> 
> 
> It should remind everybody of reviewing the new API and policies,
> and maintaining the existing code appropriately.
>