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

[Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>]

Hi Roxy,
	Thanks for the work, few questions inline.

> -----Original Message-----
> From: Rory Sexton <rory.sexton@intel.com>
> Sent: Thursday, March 23, 2023 6:38 AM
> To: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>;
> konstantin.v.ananyev@yandex.ru
> Cc: dev@dpdk.org; Rory Sexton <rory.sexton@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. 

> - 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?

> 
> 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?

> 
> 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