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

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

-----Original Message-----
> Date: Mon, 12 Mar 2018 14:30:49 +0000
> From: "Eads, Gage" <gage.eads@intel.com>
> To: Jerin Jacob <jerin.jacob@caviumnetworks.com>
> CC: "dev@dpdk.org" <dev@dpdk.org>, "Van Haaren, Harry"
>  <harry.van.haaren@intel.com>, "hemant.agrawal@nxp.com"
>  <hemant.agrawal@nxp.com>, "Richardson, Bruce"
>  <bruce.richardson@intel.com>, "santosh.shukla@caviumnetworks.com"
>  <santosh.shukla@caviumnetworks.com>, "nipun.gupta@nxp.com"
>  <nipun.gupta@nxp.com>
> Subject: RE: [PATCH v2 1/2] eventdev: add device stop flush callback
> 
> 
> 
> > -----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?

Yes. Make sense to move to rte_eventdev_ops. But need to take care
updating the those function pointers in secondary process.