(Bruce's adviced heeded :))
> -----Original Message-----
> From: Jerin Jacob [mailto:jerin.jacob at caviumnetworks.com]
> Sent: Tuesday, November 22, 2016 5:44 PM
> To: Eads, Gage <gage.eads at intel.com>
> Cc: dev at dpdk.org; Richardson, Bruce <bruce.richardson at intel.com>; Van
> Haaren, Harry <harry.van.haaren at intel.com>; hemant.agrawal at nxp.com
> Subject: Re: [dpdk-dev] [PATCH 2/4] eventdev: implement the northbound APIs
>
> On Tue, Nov 22, 2016 at 10:48:32PM +0000, Eads, Gage wrote:
> >
> >
> > > -----Original Message-----
> > > From: Jerin Jacob [mailto:jerin.jacob at caviumnetworks.com]
> > > Sent: Tuesday, November 22, 2016 2:00 PM
> > > To: Eads, Gage <gage.eads at intel.com>
> > > Cc: dev at dpdk.org; Richardson, Bruce <bruce.richardson at intel.com>;
> > > Van Haaren, Harry <harry.van.haaren at intel.com>;
> > > hemant.agrawal at nxp.com
> > > Subject: Re: [dpdk-dev] [PATCH 2/4] eventdev: implement the
> > > northbound APIs
> > >
> > > On Tue, Nov 22, 2016 at 07:43:03PM +0000, Eads, Gage wrote:
> > > > > > > > > One open issue I noticed is the "typical workflow"
> > > > > description starting in > > rte_eventdev.h:204 conflicts with
> > > the > > centralized software PMD that Harry > > posted last week.
> > > > > Specifically, that PMD expects a single core to call the > >
> > > > > schedule function. We could extend the documentation to account
> > > for > > this > > alternative style of scheduler invocation, or
> > > discuss > > ways to make the software > > PMD work with the
> > > documented > > workflow. I prefer the former, but either way I >
> > > > think we > > ought to expose the scheduler's expected usage to
> > > the user -- > > perhaps > > through an RTE_EVENT_DEV_CAP flag?
> > > > > > > >
> > > > > > > > I prefer former too, you can propose the documentation
> > > > > change required for > > software PMD.
> > > > > >
> > > > > > Sure, proposal follows. The "typical workflow" isn't the
> > > most > > optimal by having a conditional in the fast-path, of
> > > course, but it > > demonstrates the idea simply.
> > > > > >
> > > > > > (line 204)
> > > > > > * An event driven based application has following typical
> > > > > workflow on > > fastpath:
> > > > > > * \code{.c}
> > > > > > * while (1) {
> > > > > > *
> > > > > > * if (dev_info.event_dev_cap &
> > > > > > * RTE_EVENT_DEV_CAP_DISTRIBUTED_SCHED)
> > > > > > * rte_event_schedule(dev_id);
> > > > >
> > > > > Yes, I like the idea of RTE_EVENT_DEV_CAP_DISTRIBUTED_SCHED.
> > > > > It can be input to application/subsystem to launch separate
> > > > > core(s) for schedule functions.
> > > > > But, I think, the "dev_info.event_dev_cap & > >
> > > RTE_EVENT_DEV_CAP_DISTRIBUTED_SCHED"
> > > > > check can be moved inside the implementation(to make the
> > > better > > decisions and avoiding consuming cycles on HW based
> schedulers.
> > > >
> > > > How would this check work? Wouldn't it prevent any core from
> > > running the software scheduler in the centralized case?
> > >
> > > I guess you may not need RTE_EVENT_DEV_CAP here, instead need flag
> > > for device configure here
> > >
> > > #define RTE_EVENT_DEV_CFG_DISTRIBUTED_SCHED (1ULL << 1)
> > >
> > > struct rte_event_dev_config config; config.event_dev_cfg =
> > > RTE_EVENT_DEV_CFG_DISTRIBUTED_SCHED;
> > > rte_event_dev_configure(.., &config);
> > >
> > > on the driver side on configure,
> > > if (config.event_dev_cfg & RTE_EVENT_DEV_CFG_DISTRIBUTED_SCHED)
> > > eventdev->schedule = NULL;
> > > else // centralized case
> > > eventdev->schedule = your_centrized_schedule_function;
> > >
> > > Does that work?
> >
> > Hm, I fear the API would give users the impression that they can select the
> scheduling behavior of a given eventdev, when a software scheduler is more
> likely to be either distributed or centralized -- not both.
>
> Even if it is capability flag then also it is per "device". Right ?
> capability flag is more of read only too. Am i missing something here?
>
Correct, the capability flag I'm envisioning is per-device and read-only.
> >
> > What if we use the capability flag, and define rte_event_schedule() as the
> scheduling function for centralized schedulers and rte_event_dequeue() as the
> scheduling function for distributed schedulers? That way, the datapath could
> be
> the simple dequeue -> process -> enqueue. Applications would check the
> capability flag at configuration time to decide whether or not to launch an
> lcore that calls rte_event_schedule().
>
> I am all for simple "dequeue -> process -> enqueue".
> rte_event_schedule() added for SW scheduler only, now it may not make sense
> to add one more check on top of "rte_event_schedule()" to see it is really
> need
> or not in fastpath?
>
Yes, the additional check shouldn't be needed. In terms of the 'typical
workflow' description, this is what I have in mind:
*
* An event driven based application has following typical workflow on fastpath:
* \code{.c}
* while (1) {
*
* rte_event_dequeue(...);
*
* (event processing)
*
* rte_event_enqueue(...);
* }
* \endcode
*
* The events are injected to event device through the *enqueue* operation by
* event producers in the system. The typical event producers are ethdev
* subsystem for generating packet events, core(SW) for generating events based
* on different stages of application processing, cryptodev for generating
* crypto work completion notification etc
*
* The *dequeue* operation gets one or more events from the event ports.
* The application process the events and send to downstream event queue through
* rte_event_enqueue() if it is an intermediate stage of event processing, on
* the final stage, the application may send to different subsystem like ethdev
* to send the packet/event on the wire using ethdev rte_eth_tx_burst() API.
*
* The point at which events are scheduled to ports depends on the device. For
* hardware devices, scheduling occurs asynchronously. Software schedulers can
* either be distributed (each worker thread schedules events to its own port)
* or centralized (a dedicated thread schedules to all ports). Distributed
* software schedulers perform the scheduling in rte_event_dequeue(), whereas
* centralized scheduler logic is located in rte_event_schedule(). The
* RTE_EVENT_DEV_CAP_DISTRIBUTED_SCHED capability flag indicates whether a
* device is centralized and thus needs a dedicated scheduling thread that
* repeatedly calls rte_event_schedule().
*
*/
