Re: [dpdk-dev] [RFC] [PATCH v2] libeventdev: event driven programming model framework for DPDK

[Jerin Jacob <jerin.jacob@caviumnetworks.com>]

On Fri, Oct 14, 2016 at 05:02:21PM +0100, Bruce Richardson wrote:
> On Wed, Oct 12, 2016 at 01:00:16AM +0530, Jerin Jacob wrote:
> > Thanks to Intel and NXP folks for the positive and constructive feedback
> > I've received so far. Here is the updated RFC(v2).
> > 
> > I've attempted to address as many comments as possible.
> > 
> > This series adds rte_eventdev.h to the DPDK tree with
> > adequate documentation in doxygen format.
> > 
> > Updates are also available online:
> > 
> > Related draft header file (this patch):
> > https://rawgit.com/jerinjacobk/libeventdev/master/rte_eventdev.h
> > 
> > PDF version(doxgen output):
> > https://rawgit.com/jerinjacobk/libeventdev/master/librte_eventdev_v2.pdf
> > 
> > Repo:
> > https://github.com/jerinjacobk/libeventdev
> > 
> 
> Thanks for all the work on this.

Thanks

> 
> <snip>
> > +/* Event device configuration bitmap flags */
> > +#define RTE_EVENT_DEV_CFG_PER_DEQUEUE_WAIT (1 << 0)
> > +/**< Override the global *dequeue_wait_ns* and use per dequeue wait in ns.
> > + *  \see rte_event_dequeue_wait_time(), rte_event_dequeue()
> > + */
> 
> Can you clarify why this is needed? If an app wants to use the same
> dequeue wait times for all dequeues can it not specify that itself via
> the wait time parameter, rather than having a global dequeue wait value?

The rational for choosing this scheme to have optimized
rte_event_dequeue() for some implementation without loosing application
portability and need.

We mostly have two different types of HW schemes to define the wait time

HW1) Have only global wait value for the eventdev across all the
dequeue
HW2) Per queue wait value

In-terms of applications,
APP1) Trivial application does not need different dequeue value for each
dequeue
APP2) Non trivial applications does need different dequeue values

This config option can take advantage if application demands only APP1
on HW1 without loosing application potablity.(i.e if application demand
for APP2 scheme then HW1 based implementation can have different function
pointer to implement dequeue function)

The overall theme of the proposal to have more configuration options(like
RTE_EVENT_QUEUE_CFG_SINGLE_CONSUMER) to have high performance SW/HW implementations