Re: [dpdk-dev] ABI and inline functions

[Stephen Hemminger <stephen@networkplumber.org>]

On Wed, 17 Apr 2019 17:46:34 +0000
Jerin Jacob Kollanukkaran <jerinj@marvell.com> wrote:

> > -----Original Message-----
> > From: dev <dev-bounces@dpdk.org> On Behalf Of Bruce Richardson
> > Sent: Wednesday, April 17, 2019 2:07 PM
> > To: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>
> > Cc: dev@dpdk.org; Stephen Hemminger <stephen@networkplumber.org>;
> > Ananyev, Konstantin <konstantin.ananyev@intel.com>; thomas@monjalon.net;
> > Ray Kinsella <mdr@ashroe.eu>; nd <nd@arm.com>
> > Subject: Re: [dpdk-dev] ABI and inline functions
> >   
> > > 2) Every function that is not in the direct datapath (fastpath?)
> > > should not be inline. Exceptions or things like rx/tx burst, ring
> > > enqueue/dequeue, and packet alloc/free - Stephen  
> > 
> > Agree with this. Anything not data path should not be inline. The next question
> > then is for data path items how to determine whether they need to be inline or
> > not. In general my rule-of-thumb:
> > * anything dealing with bursts of packets should not be inline  
> 
> # I think, we need consider the how fat is the function too,
> If it is light weight, probably we need to make it inline
> # Except the forward case, In real world use case, it is not trivial make large 
> burst of packet to process it even though function prototype burst.
> We may need to consider that
> # For the given function if some argument is used with inline other function,
>  probably no point in making that function alone  inline as the structure 
> is exposed in some other function.
> 
> > * anything what works with single packet at a time should be inline
> >   
> > > In this context, does it make sense to say that we will maintain API
> > > compatibility rather than saying ABI compatibility? This will also
> > > send the right message to the end users.
> > >  
> > I would value ABI compatibility much higher than API compatibility. If someone
> > is recompiling the application anyway, making a couple of small changes (large
> > rework is obviously a different issue) to the code should not be a massive issue, I
> > hope. On the other hand, ABI compatibility is needed to allow seamless update
> > from one version to another, and it's that ABI compatiblity that allows distro's to
> > pick up our latest and greatest versions.  
> 
> IMO, We have two primary use case for DPDK
> 
> 1) NFV kind of use case 	where the application needs to run on multiple platform
> without recompiling it.
> 2) Fixed appliance use case where embed SoC like Intel Denverton or ARM64 integrated
> Controller used. For fixed appliance use case, end user care more of performance
> than ABI compatibility as it easy to recompile the end user application vs the cost of
> hitting performance impact.

Nobody cares about compatiablity until they have to the first security update.