System will deadlock if your application decides to step out from the schedule loop, and a throughput optimized scheduler has already pre-scheduled a number of buffers to that core (== locked a number of atomic queues).
Application has to be sure that scheduler has not locked anything for that core before stepping out of the schedule loop. Typically, it’s impossible for the HW scheduler to rewind scheduling decision afterwards (when application tells it wants to exit). -Petri From: ext Bill Fischofer [mailto:[email protected]] Sent: Wednesday, October 15, 2014 4:38 PM To: Savolainen, Petri (NSN - FI/Espoo) Cc: ext Alexandru Badicioiu; Ola Liljedahl; [email protected] Subject: Re: [lng-odp] odp_schedule() vs. odp_schedule_one() It's not clear why you'd want to expose implementation considerations through the API. That's what DPDK does and it gets them into all sorts of portability trouble. odp_schedule() is how a thread discovers the next thing it's supposed to do. From that standpoint there doesn't appear to be any application-visible distinction between odp_schedule() and odp_schedule_one(). In both cases, the application gets a buffer, as well as the queue it was drawn from. That's all the application needs to know--everything else is behind-the-scenes implementation mechanics that will vary from platform to platform. On Wed, Oct 15, 2014 at 8:13 AM, Savolainen, Petri (NSN - FI/Espoo) <[email protected]<mailto:[email protected]>> wrote: Hi, It’s not only push vs pull. It can be also “pull many” vs “pull one”. Alex, I think your HW supports both: pull many or pull only one. Global scheduling == SoC level scheduling, not scheduling from e.g. per core level stash of (pre-scheduled) buffers/queues. The first goal of the function is to streamline application main loop when application have to step out of the schedule loop often (e.g. in addition to ODP scheduler, poll a third party lib). So instead of ... main_odp_loop { odp_schedule_resume() buf = odp_schedule(...) <process it> odp_schedule_pause() while ( (buf = odp_schedule(...)) != INVALID) { <process it> } odp_schedule_release_atomic() return } ... you can do ... main_odp_loop { buf = odp_schedule_one(...) <process it> odp_schedule_release_atomic() return } The second goal is to optimize for QoS response time. It could be handled with another call that tells ODP to optimize for QoS instead of throughput. -Petri From: [email protected]<mailto:[email protected]> [mailto:[email protected]<mailto:[email protected]>] On Behalf Of ext Alexandru Badicioiu Sent: Wednesday, October 15, 2014 3:52 PM To: Ola Liljedahl Cc: [email protected]<mailto:[email protected]> Subject: Re: [lng-odp] odp_schedule() vs. odp_schedule_one() The documentation suggests that these two calls can be used in the same application which may be a problem also for platforms which do support both modes, but not at the same time or without re-initialization, re-configuration, etc. By modes I mean PUSH (odp_schedule()), when the scheduler runs independently of the application and pushes frames to the application, and PULL (odp_schedule_one()) when the scheduler runs when the application decides and the application pulls the frames from the scheduler. Also the term "global scheduling" is confusing and may not reflect the reality of the HW. Alex On 15 October 2014 15:15, Ola Liljedahl <[email protected]<mailto:[email protected]>> wrote: * Schedule one buffer * * Like odp_schedule(), but is quaranteed to schedule only one buffer at a time. * Each call will perform global scheduling and will reserve one buffer per * thread in maximum. When called after other schedule functions, returns * locally stored buffers (if any) first, and then continues in the global * scheduling mode. * * This function optimises priority scheduling (over throughput). As Taras commented, some implementations will not be able to truly schedule only one event at a time. Scheduler implementations could use a pipelined designed where events are scheduled in advance so that the next event can be prefetched while the current event is being processed. This will limit concurrent processing (e.g. an idle core could have received that second event and process it concurrently, this would have reduced latency for that event). odp_schedule_one() has the same functionality as odp_schedule(). However it is supposed to guarantee only one event at a time is scheduled in order to prioritize latency to the potential detriment of throughput. We question whether odp_schedule_one() actually has to guarantee only one event at a time. The functionality provided is the same for these two calls. One call is focused on throughput (and minimizing overhead, e.g.by<http://e.g.by> allowing prescheduling and do prefetching), the other is focused on latency (at the cost of overhead). An ODP implementation could use the same implementation for both functions (some ODP implementations will always schedule events in advance, other implementations will always only schedule one event at a time). odp_schedule_one() just hints the ODP implementations that latency and concurrent processing is more important but this is not a strict requirement. Maybe we only need one schedule call and possibly use a different mechanism to hint the ODP scheduler whether to optimize for throughput (e.g. preschedule/prefetch) or latency. --Ola _______________________________________________ lng-odp mailing list [email protected]<mailto:[email protected]> http://lists.linaro.org/mailman/listinfo/lng-odp _______________________________________________ lng-odp mailing list [email protected]<mailto:[email protected]> http://lists.linaro.org/mailman/listinfo/lng-odp
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