Re: rte_ring features in use (or not)

[Olivier Matz <olivier.matz@6wind.com>]

On Wed, 25 Jan 2017 17:29:18 +0000, "Ananyev, Konstantin"
<konstantin.ananyev@intel.com> wrote:
> > > > Bonus question:
> > > > * Do we know how widely used the enq_bulk/deq_bulk functions
> > > > are? They are useful for unit tests, so they do have uses, but
> > > > I think it would be good if we harmonized the return values
> > > > between bulk and burst functions. Right now:
> > > >    enq_bulk  - only enqueues all elements or none. Returns 0
> > > > for all, or negative error for none.
> > > >    enq_burst - enqueues as many elements as possible. Returns
> > > > the number enqueued.  
> > >
> > > I do use the apis in pktgen and the difference in return values
> > > has got me once. Making them common would be great,  but the
> > > problem is  
> > backward compat to old versions I would need to have an ifdef in
> > pktgen now. So it seems like we moved the problem to the
> > application.  
> > >  
> > 
> > Yes, an ifdef would be needed, but how many versions of DPDK back
> > do you support? Could the ifdef be removed again after say, 6
> > months? 
> > > I would like to see the old API kept and a new API with the new
> > > behavior. I know it adds another API but one of the API would be
> > > nothing  
> > more than wrapper function if not a macro.  
> > >
> > > Would that be more reasonable then changing the ABI?  
> > 
> > Technically, this would be an API rather than ABI change, since the
> > functions are inlined in the code. However, it's not the only API
> > change I'm looking to make here - I'd like to have all the
> > functions start returning details of the state of the ring, rather
> > than have the watermarks facility. If we add all new functions for
> > this and keep the old ones around, we are just increasing our
> > maintenance burden.
> > 
> > I'd like other opinions here. Do we see increasing the API surface
> > as the best solution, or are we ok to change the APIs of a key
> > library like the rings one?  
> 
> I am ok with changing API to make both _bulk and _burst return the
> same thing. Konstantin 

I agree that the _bulk() functions returning 0 or -err can be confusing.
But it has at least one advantage: it explicitly shows that if user ask
for N enqueues/dequeues, it will either get N or 0, not something
between.

Changing the API of the existing _bulk() functions looks a bit
dangerous to me. There's probably a lot of code relying on the ring
API, and changing its behavior may break it.

I'd prefer to deprecate the old _bulk and _burst functions, and
introduce a new api, maybe something like:

  rte_ring_generic_dequeue(ring, objs, n, behavior, flags)
  -> return nb_objs or -err


Olivier