Re: [dpdk-dev] [PATCH v2 1/2] eventdev: add device stop flush callback

["Eads, Gage" <gage.eads@intel.com>]

> -----Original Message-----
> From: Jerin Jacob [mailto:jerin.jacob@caviumnetworks.com]
> Sent: Monday, March 12, 2018 1:25 AM
> To: Eads, Gage <gage.eads@intel.com>
> Cc: dev@dpdk.org; Van Haaren, Harry <harry.van.haaren@intel.com>;
> hemant.agrawal@nxp.com; Richardson, Bruce <bruce.richardson@intel.com>;
> santosh.shukla@caviumnetworks.com; nipun.gupta@nxp.com
> Subject: Re: [PATCH v2 1/2] eventdev: add device stop flush callback
> 
> -----Original Message-----
> > When an event device is stopped, it drains all event queues. These
> > events may contain pointers, so to prevent memory leaks eventdev now
> > supports a user-provided flush callback that is called during the queue drain
> process.
> > This callback is stored in process memory, so the callback must be
> > registered by any process that may call rte_event_dev_stop().
> >
> > This commit also clarifies the behavior of rte_event_dev_stop().
> >
> > This follows this mailing list discussion:
> > http://dpdk.org/ml/archives/dev/2018-January/087484.html
> >
> > Signed-off-by: Gage Eads <gage.eads@intel.com>
> > ---
> > v2: allow a NULL callback pointer to unregister the callback
> >
> >  lib/librte_eventdev/rte_eventdev.c           | 17 +++++++++
> >  lib/librte_eventdev/rte_eventdev.h           | 55
> +++++++++++++++++++++++++++-
> >  lib/librte_eventdev/rte_eventdev_version.map |  6 +++
> >  3 files changed, 76 insertions(+), 2 deletions(-)
> >
> > diff --git a/lib/librte_eventdev/rte_eventdev.c
> > b/lib/librte_eventdev/rte_eventdev.c
> > index 851a119..1aacb7b 100644
> > --- a/lib/librte_eventdev/rte_eventdev.c
> > +++ b/lib/librte_eventdev/rte_eventdev.c
> > @@ -1123,6 +1123,23 @@ rte_event_dev_start(uint8_t dev_id)
> >  	return 0;
> >  }
> >
> > +typedef void (*eventdev_stop_flush_t)(uint8_t dev_id, struct rte_event event,
> > +		void *arg);
> > +/**< Callback function called during rte_event_dev_stop(), invoked
> > +once per
> > + * flushed event.
> > + */
> > +
> >  #define RTE_EVENTDEV_NAME_MAX_LEN	(64)
> >  /**< @internal Max length of name of event PMD */
> >
> > @@ -1176,6 +1194,11 @@ struct rte_eventdev {
> >  	event_dequeue_burst_t dequeue_burst;
> >  	/**< Pointer to PMD dequeue burst function. */
> >
> > +	eventdev_stop_flush_t dev_stop_flush;
> > +	/**< Optional, user-provided event flush function */
> > +	void *dev_stop_flush_arg;
> > +	/**< User-provided argument for event flush function */
> > +
> 
> I think, we can move this additions to the internal rte_eventdev_data structure.
> Reasons are
> 1) Changes to "struct rte_eventdev" would call for ABI change
> 2) We can keep "struct rte_eventdev" only for fast path functions, slow path
> functions can have additional redirection.
> 

Good points -- I hadn't considered the ABI impact of modifying rte_eventdev. rte_eventdev_data is in shared memory, though, so it's not multi-process friendly for function pointers. How about putting it in rte_eventdev_ops?

> >  	struct rte_eventdev_data *data;
> >  	/**< Pointer to device data */
> >  	const struct rte_eventdev_ops *dev_ops; @@ -1822,6 +1845,34 @@
> > rte_event_dev_xstats_reset(uint8_t dev_id,
> >   */
> >  int rte_event_dev_selftest(uint8_t dev_id);
> >
> > +/**
> > + * Registers a callback function to be invoked during
> > +rte_event_dev_stop() for
> > + * each flushed event. This function can be used to properly dispose
> > +of queued
> > + * events, for example events containing memory pointers.
> > + *
> > + * The callback function is only registered for the calling process.
> > +The
> > + * callback function must be registered in every process that can
> > +call
> > + * rte_event_dev_stop().
> > + *
> > + * To unregister a callback, call this function with a NULL callback pointer.
> > + *
> > + * @param dev_id
> > + *   The identifier of the device.
> > + * @param callback
> > + *   Callback function invoked once per flushed event.
> > + * @param userdata
> > + *   Argument supplied to callback.
> > + *
> > + * @return
> > + *  - 0 on success.
> > + *  - -EINVAL if *dev_id* is invalid
> > + *
> > + * @see rte_event_dev_stop()
> > + */
> > +int
> > +rte_event_dev_stop_flush_callback_register(uint8_t dev_id,
> > +		eventdev_stop_flush_t callback, void *userdata);
> > +
> IMO, It would be better if we place this function near to rte_event_dev_stop().
> 
> Other than above minor changes, It looks good to me.

Ok, will address in v3.

Thanks,
Gage