[RFC 0/1] ring: add callback infrastructire to ring library

[Sexton, Rory]

Hi Honnappa,

Responses inline.
I will continue with an initial implementation of this feature and capture performance data as suggested. 

Rgds,
Rory

> -----Original Message-----
> From: Honnappa Nagarahalli <Honnappa.Nagarahalli at arm.com> 
> Sent: Wednesday, April 5, 2023 1:46 AM
> To: Sexton, Rory <rory.sexton at intel.com>; konstantin.v.ananyev at yandex.ru
> Cc: dev at dpdk.org; nd <nd at arm.com>; nd <nd at arm.com>
> Subject: RE: [RFC 0/1] ring: add callback infrastructire to ring library
> 
> Hi Roxy,
> 	Thanks for the work, few questions inline.
> 
> > -----Original Message-----
> > From: Rory Sexton <rory.sexton at intel.com>
> > Sent: Thursday, March 23, 2023 6:38 AM
> > To: Honnappa Nagarahalli <Honnappa.Nagarahalli at arm.com>; 
> > konstantin.v.ananyev at yandex.ru
> > Cc: dev at dpdk.org; Rory Sexton <rory.sexton at intel.com>
> > Subject: [RFC 0/1] ring: add callback infrastructire to ring library
> > 
> > This is an RFC proposing the addition of a callback infrastructure to 
> > the ring library, particularly in the ring dequeue functions, but they 
> > could also be added to the enqueue functions if desired.
> > 
> > Callbacks in the ring dequeue functions would be beneficial for a 
> > number of reasons including but not limited to the following:
> > - would allow users to register specific functions to be called on dequeue of a
> >   ring avoiding the need to call the function within application code on several
> >   threads reading from said ring.
> I do not completely understand the 'avoiding the need to call the function within application code on several threads reading from said ring'. Irrespective of where the feature is implemented (either in ring library or the application), the call back function will be called on all the threads that receive from this queue. 
I just mean the callback infrastructure would handle the call back function rather than developer needing to call their implemented function explicitely 

> 
> > - would mirror the callback functionality offered by the ethdev library for
> >   threads that read exclusively from a ring and process packets based off that,
> >   thus allowing for the same threads to read from either a NIC i/f or directly
> >   from a ring without needing a different codepath.
> Do you plan to support a chain of callbacks?
Yes I would plan to support a chain of callbacks 

> 
> > 
> > The addition of callbacks wouldn't impact the reading of rings by more 
> > than 1 cycle when no callbacks are registered. They could also 
> > additionally be compiled in/out as desired to give more confidence in 
> > maintaining performance when callbacks are not required.
> I would prefer to keep this feature on always as maintenance is easier. But, I think we should make that decision only after we have performance data. Is it possible to provide some performance data with this feature on but no callbacks registered?
Agreed that keeping the feature always on would be easier long-term.
I can capture performance data with the feature on but no callbacks registered.
We can base the final implementation with that data in mind. 

> 
> > 
> > This RFC is to give a feel for what the additional APIs would be and 
> > how they would be integrated within the ring dequeue functions. As 
> > such only function declarations are present. If there is a willingness 
> > within the community to add callback infrastructure to the ring library I will implement further code.
> > 
> > Rory Sexton (1):
> >   ring: add infrastructure to allow callbacks within the ring library
> > 
> >  lib/ring/rte_ring.h      | 133 ++++++++++++++++++++++++++++++++++++++-
> >  lib/ring/rte_ring_core.h |   3 +
> >  2 files changed, 135 insertions(+), 1 deletion(-)
> > 
> > --
> > 2.34.1