Re: [dpdk-dev] Bulk dequeue of packets and the returned values, question

["Ananyev, Konstantin" <konstantin.ananyev@intel.com>]

> -----Original Message-----
> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Bruce Richardson
> Sent: Monday, September 29, 2014 1:10 PM
> To: Wiles, Roger Keith (Wind River)
> Cc: dev@dpdk.org
> Subject: Re: [dpdk-dev] Bulk dequeue of packets and the returned values, question
> 
> On Sun, Sep 28, 2014 at 11:06:17PM +0000, Wiles, Roger Keith wrote:
> > Thanks Venky,
> > On Sep 28, 2014, at 5:23 PM, Venkatesan, Venky <venky.venkatesan@intel.com> wrote:
> >
> > > Keith,
> > >
> > > On 9/28/2014 11:04 AM, Wiles, Roger Keith wrote:
> > >> I am also looking at the bulk dequeue routines, which the ring can be fixed or variable. On fixed  < 0 on error is returned and 0 if
> successful. On a variable ring < 0 on error or n on success, but I think n can be zero in the variable case, correct?
> > >>
> > >> If these are true then why not have the routines return  < 0 on error and >= 0 on success. Which means a dequeue from a fixed
> ring would return only ’requested size n’ or < 0 if you error off the 0 case. The 0 case could be OK, if you allow zero to be return on a
> empty ring for the fixed ring case.
> > >>
> > >> Does this make sense to anyone?
> > > It won't make sense unless you're aware of the history behind these functions. The original functions that were implemented for
> the ring were only the bulk functions (i.e. FIXED). They would return exactly the number of items requested for dequeue (0 if success,
> negative if error), and not return any if the required number were not available.
> > >
> > > The burst (i.e. VARIABLE) functions came in much later (think it was r1.3 where we introduced them), and by that time, there were
> already quite a number of deployments of DPDK in the field using the legacy ring functions. Therefore we made the decision to keep
> the legacy behavior intact & not impacting deployed code - and merging the burst functions into the code. Given that there was no
> "versioning" of the API/ABI in those releases :).
> >
> > I see why the code is this way. If the developers used ‘if ( ret == 0 ) { /* do something */ }’ then it would break if it returned a
> positive value on success. I would expect the normal behavior to be ‘if ( ret < 0 ) { /* error case */ }’ and fall thru for the success case. I
> would love to change the code to just return <0 on error or >= 0 on success. I wonder how many customers code would break
> changing the code to do just just the two steps. I think it will remove some code in a couple places that were testing for FIXED or
> VARIABLE?
> > >
> > > Hope that helps.
> > > -Venky
> > >
> > >>
> > >> Thanks
> > >> ++Keith
> > >>
> > >> Keith Wiles, Principal Technologist with CTO office, Wind River mobile 972-213-5533
> >
> > Keith Wiles, Principal Technologist with CTO office, Wind River mobile 972-213-5533
> >
> 
> Since we are looking at making considerable ABI changes in this release and
> (hopefully) also looking to version our ABI going forward, I would be in
> favour of making any changes to these APIs in this current release if
> possible. While the current behaviour makes sense for historical reason, I
> think an overall change to the behaviour as Keith describes would be more
> sensible long-term.

It is doable, I suppose, but might become quite messy:
Don't know how many people are using  rte_ring_dequeue_bulk() all over the place.
I suspect quite a lot.
From other side - what the real gain we'll have from it?
I don't see much so far. 
Konstantin

> 
> (Also to note my previous suggestion about upping the major version to 2.0
> if we continue to increase the number of ABI/API changes in this release.
> Anyone else any thoughts on that?)
> 
>