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? > > 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? > > > > > > > > > > > > > > > * > > > > > * rte_event_dequeue(...); > > > > > * > > > > > * (event processing) > > > > > * > > > > > * rte_event_enqueue(...); > > > > > * } > > > > > * \endcode > > > > > * > > > > > * The *schedule* operation is intended to do event scheduling, > > > > and the > * *dequeue* operation returns the scheduled events. An > > > > implementation > * is free to define the semantics between > > > > *schedule* and *dequeue*. For > * example, a system based on a > > > > hardware scheduler can define its > * rte_event_schedule() to be > > > > an NOOP, whereas a software scheduler can use > * the *schedule* > > > > operation to schedule events. The > * > > > > RTE_EVENT_DEV_CAP_DISTRIBUTED_SCHED capability flag indicates > > > > whether > * rte_event_schedule() should be called by all cores or > > > > by a single (typically > * dedicated) core. > > > > > > > > > > (line 308) > > > > > #define RTE_EVENT_DEV_CAP_DISTRIBUTED_SCHED (1ULL < 2) > /**< > > > > Event scheduling implementation is distributed and all cores must > > > > execute > * rte_event_schedule(). If unset, the implementation is > > > > centralized and > * a single core must execute the schedule > > > > operation. > > > > > * > > > > > * \see rte_event_schedule() > > > > > */ > > > > > > > > > > > > > > > > > > > On same note, If software PMD based workflow need a > > > > separate core(s) for > > > schedule function then, Can we hide > > > > that from API specification and pass an > > > argument to SW pmd > > > > to define the scheduling core(s)? > > > > > > > > > > > > > > Something like --vdev=eventsw0,schedule_cmask=0x2 > > > > > > > > > > An API for controlling the scheduler coremask instead of (or > > > > perhaps in addition to) the vdev argument would be good, to allow > > > > runtime control. I can imagine apps that scale the number of cores > > > > based on load, and in doing so may want to migrate the scheduler to a > > different core. > > > > > > > > Yes, an API for number of scheduler core looks OK. But if we are > > > > going to have service core approach then we just need to specify at > > > > one place as application will not creating the service functions. > > > > > > > > > > > > > > > > > > > > > Just a thought, > > > > > > > > > > > > Perhaps, We could introduce generic "service" cores concept to > > > > DPDK to hide > > the > > requirement where the implementation > > > > needs dedicated core to do certain > > work. I guess it would > > > > useful for other NPU integration in DPDK. > > > > > > > > > > > > > > > > That's an interesting idea. As you suggested in the other thread, > > > > this concept could be extended to the "producer" code in the > > > > example for configurations where the NIC requires software to feed > > > > into the eventdev. And to the other subsystems mentioned in your > > original > > PDF, crypto and timer. > > > > > > > > Yes. Producers should come in service core category. I think, that > > > > enables us to have better NPU integration.(same application code for > > > > NPU vs non NPU) > > > >
