From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Van Haaren, Harry" <harry.van.haaren@intel.com>
Subject: Re: [PATCH v4 1/2] eventdev: add device stop flush
	callback
Date: Fri, 23 Mar 2018 16:57:25 +0000
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To: "Eads, Gage" <gage.eads@intel.com>, "dev@dpdk.org" <dev@dpdk.org>
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> From: Eads, Gage
> Sent: Tuesday, March 20, 2018 2:13 PM
> To: dev@dpdk.org
> Cc: jerin.jacob@caviumnetworks.com; 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: [PATCH v4 1/2] eventdev: add device stop flush callback
>=20
> 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 proces=
s.
> This callback is stored in process memory, so the callback must be
> registered by any process that may call rte_event_dev_stop().
>=20
> This commit also clarifies the behavior of rte_event_dev_stop().
>=20
> This follows this mailing list discussion:
> http://dpdk.org/ml/archives/dev/2018-January/087484.html
>=20
> Signed-off-by: Gage Eads <gage.eads@intel.com>

<snip most of the code - looks good!>

>  /**
> - * Stop an event device. The device can be restarted with a call to
> - * rte_event_dev_start()
> + * Stop an event device.
> + *
> + * This function causes all queued events to be drained. While draining
> events
> + * out of the device, this function calls the user-provided flush callba=
ck
> + * (if one was registered) once per event.
> + *
> + * This function does not drain events from event ports; the application=
 is
> + * responsible for flushing events from all ports before stopping the
> device.


Question about how an application is expected to correctly cleanup all the
events here. Note in particular the last part: "application is responsible
for flushing events from all ports **BEFORE** stopping the device".

Given the event device is still running, how can the application be sure it=
 has
flushed all the events (from the dequeue side in particular)?


In order to drain all events from the ports, I was expecting the following:

// stop scheduling new events to worker cores
rte_event_dev_stop()
---> callback gets called for each event

// to dequeue events from each port, and app cleans them up?
FOR_EACH_PORT( rte_event_dev_dequeue(..., port_id, ...) )


I'd like to avoid the dequeue-each-port() approach in application, as it ad=
ds
extra burden to clean up correctly...

What if we say that dequeue() returns zero after stop() (leaving events pos=
sibly
in the port-dequeue side SW buffers), and these events which were about to
be dequeued by the worker core are also passed to the dev_stop_flush callba=
ck?