[dpdk-dev] [PATCH v2 1/6] eventdev: introduce event driven programming model

Bruce Richardson bruce.richardson at intel.com
Thu Dec 8 10:57:52 CET 2016


On Thu, Dec 08, 2016 at 07:18:01AM +0530, Jerin Jacob wrote:
> On Wed, Dec 07, 2016 at 11:12:51AM +0000, Bruce Richardson wrote:
> > On Tue, Dec 06, 2016 at 09:22:15AM +0530, Jerin Jacob wrote:
> > > In a polling model, lcores poll ethdev ports and associated
> > > rx queues directly to look for packet. In an event driven model,
> > > by contrast, lcores call the scheduler that selects packets for
> > > them based on programmer-specified criteria. Eventdev library
> > > adds support for event driven programming model, which offer
> > > applications automatic multicore scaling, dynamic load balancing,
> > > pipelining, packet ingress order maintenance and
> > > synchronization services to simplify application packet processing.
> > > 
> > > By introducing event driven programming model, DPDK can support
> > > both polling and event driven programming models for packet processing,
> > > and applications are free to choose whatever model
> > > (or combination of the two) that best suits their needs.
> > > 
> > > This patch adds the eventdev specification header file.
> > > 
> > > Signed-off-by: Jerin Jacob <jerin.jacob at caviumnetworks.com>
> > > ---
> > > +
> > > +/**
> > > + * Link multiple source event queues supplied in *rte_event_queue_link*
> > > + * structure as *queue_id* to the destination event port designated by its
> > > + * *port_id* on the event device designated by its *dev_id*.
> > > + *
> > > + * The link establishment shall enable the event port *port_id* from
> > > + * receiving events from the specified event queue *queue_id*
> > > + *
> > > + * An event queue may link to one or more event ports.
> > > + * The number of links can be established from an event queue to event port is
> > > + * implementation defined.
> > > + *
> > > + * Event queue(s) to event port link establishment can be changed at runtime
> > > + * without re-configuring the device to support scaling and to reduce the
> > > + * latency of critical work by establishing the link with more event ports
> > > + * at runtime.
> > > + *
> > > + * @param dev_id
> > > + *   The identifier of the device.
> > > + *
> > > + * @param port_id
> > > + *   Event port identifier to select the destination port to link.
> > > + *
> > > + * @param link
> > > + *   Points to an array of *nb_links* objects of type *rte_event_queue_link*
> > > + *   structure which contain the event queue to event port link establishment
> > > + *   attributes.
> > > + *   NULL value is allowed, in which case this function links all the configured
> > > + *   event queues *nb_event_queues* which previously supplied to
> > > + *   rte_event_dev_configure() to the event port *port_id* with normal servicing
> > > + *   priority(RTE_EVENT_DEV_PRIORITY_NORMAL).
> > > + *
> > > + * @param nb_links
> > > + *   The number of links to establish
> > > + *
> > > + * @return
> > > + * The number of links actually established. The return value can be less than
> > > + * the value of the *nb_links* parameter when the implementation has the
> > > + * limitation on specific queue to port link establishment or if invalid
> > > + * parameters are specified in a *rte_event_queue_link*.
> > > + * If the return value is less than *nb_links*, the remaining links at the end
> > > + * of link[] are not established, and the caller has to take care of them.
> > > + * If return value is less than *nb_links* then implementation shall update the
> > > + * rte_errno accordingly, Possible rte_errno values are
> > > + * (-EDQUOT) Quota exceeded(Application tried to link the queue configured with
> > > + *  RTE_EVENT_QUEUE_CFG_FLAG_SINGLE_LINK to more than one event ports)
> > > + * (-EINVAL) Invalid parameter
> > > + *
> > > + */
> > > +int
> > > +rte_event_port_link(uint8_t dev_id, uint8_t port_id,
> > > +		    const struct rte_event_queue_link link[],
> > > +		    uint16_t nb_links);
> > > +
> > 
> > Hi again Jerin,
> > 
> > another small suggestion here. I'm not a big fan of using small
> > structures to pass parameters into functions, especially when not all
> > fields are always going to be used. Rather than use the event queue link
> > structure, can we just pass in two array parameters here - the list of
> > QIDs, and the list of priorities. In cases where the eventdev
> > implementation does not support link prioritization, or where the app
> > does not want different priority mappings , then the second
> > array can be null [implying NORMAL priority for the don't care case].
> > 
> > 	int
> > 	rte_event_port_link(uint8_t dev_id, uint8_t port_id,
> > 		const uint8_t queues[], const uint8_t priorities[],
> > 		uint16_t nb_queues);
> > 
> > This just makes mapping an array of queues easier, as we can just pass
> > an array of ints directly in, and it especially makes it easier to
> > create a single link via:
> > 
> >   rte_event_port_link(dev_id, port_id, &queue_id, NULL, 1);
> 
> The reason why I thought of creating "struct rte_event_queue_link",
> - Its easy to add new parameter in link attributes if required

Make the priority value be in a struct, perhaps. That would allow for
future expansion, while still making it easier for the case where people
just want the mappings without any prioritization.

> - Its _easy_ to implement PAUSE and RESUME in application
> 
> PAUSE:
> nr_links = rte_event_port_links_get(,,link)
> rte_event_port_unlink_all
> 
> RESUME:
> rte_event_port_link(,,link, nr_links);

Ok, I had missed that implication. Since that is probably an important
operation we might want to do, perhaps links_get API should be updated
too to keep parameter matching.

/Bruce


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