(+Liang Ma for OPDL maintainer) Ping to maintainers, is the below suggestion acceptable for your PMDs?
Summary of suggestion: - After event_dev_stop() dequeue() is no longer allowed on any thread - All events in the system (queues, ports, intermediary buffers) will be passed to a user-supplied callback for cleaning up events. > -----Original Message----- > From: dev [mailto:dev-boun...@dpdk.org] On Behalf Of Van Haaren, Harry > Sent: Tuesday, March 27, 2018 9:20 AM > To: Eads, Gage <gage.e...@intel.com>; jerin.ja...@caviumnetworks.com; > hemant.agra...@nxp.com > Cc: Richardson, Bruce <bruce.richard...@intel.com>; > santosh.shu...@caviumnetworks.com; nipun.gu...@nxp.com; dev@dpdk.org > Subject: Re: [dpdk-dev] [PATCH v4 1/2] eventdev: add device stop flush > callback > > > From: Eads, Gage > > Sent: Monday, March 26, 2018 10:59 PM > > To: Van Haaren, Harry <harry.van.haa...@intel.com>; dev@dpdk.org > > Cc: jerin.ja...@caviumnetworks.com; hemant.agra...@nxp.com; Richardson, > Bruce > > <bruce.richard...@intel.com>; santosh.shu...@caviumnetworks.com; > > nipun.gu...@nxp.com > > Subject: RE: [PATCH v4 1/2] eventdev: add device stop flush callback > > > > > > > > > -----Original Message----- > > > From: Van Haaren, Harry > > > Sent: Friday, March 23, 2018 11:57 AM > > > To: Eads, Gage <gage.e...@intel.com>; dev@dpdk.org > > > Cc: jerin.ja...@caviumnetworks.com; hemant.agra...@nxp.com; Richardson, > > > Bruce <bruce.richard...@intel.com>; santosh.shu...@caviumnetworks.com; > > > nipun.gu...@nxp.com > > > Subject: RE: [PATCH v4 1/2] eventdev: add device stop flush callback > > > > > > > From: Eads, Gage > > > > Sent: Tuesday, March 20, 2018 2:13 PM > > > > To: dev@dpdk.org > > > > Cc: jerin.ja...@caviumnetworks.com; Van Haaren, Harry > > > > <harry.van.haa...@intel.com>; hemant.agra...@nxp.com; Richardson, > > > > Bruce <bruce.richard...@intel.com>; santosh.shu...@caviumnetworks.com; > > > > nipun.gu...@nxp.com > > > > Subject: [PATCH v4 1/2] eventdev: add device stop flush callback > > > > > > > > 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.e...@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 > > > > + callback > > > > + * (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)? > > > > > > > Appreciate the feedback -- good points all around. > > > > I was expecting that the application would unlink queues from the ports, > and > > then dequeue until each port has no events. However, there are PMDs for > which > > runtime port link/unlink is not supported, so I see that this is not a > viable > > approach. Plus, this adds the application burden that you describe below. > > +1. > > > > > > > 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 > > adds extra > > > burden to clean up correctly... > > > > Agreed, but for a different reason: that approach means we'd have to > change > > the documented eventdev behavior. rte_eventdev.h states that the > "schedule, > > enqueue and dequeue functions should not be invoked when the device is > > stopped," and this patch reiterates that in the rte_event_dev_stop() > > documentation ("Threads that continue to enqueue/dequeue while the device > is > > stopped, or being stopped, will result in undefined behavior"). Since a > PMD's > > stop cleanup code could just be repeated calls to a PMD's dequeue code, > > allowing applications to dequeue simultaneously could be troublesome. > > All +1 too, good point about the header stating it is undefined behavior. > > > > > What if we say that dequeue() returns zero after stop() (leaving events > > possibly > > > 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 > callback? > > > > I'd prefer to have dequeue-while-stopped be unsupported, so we don't need > an > > additional check or synchronization in the datapath, but passing the > events in > > a port to the callback should work (for the sw PMD, at least). How does > that > > sound? > > > That's fine with me, both from design point of view, and SW PMD. > > @HW PMD maintainers, would the above approach work for you? > > >
