Signed-off-by: Ivan Khoronzhuk <ivan.khoronz...@linaro.org> Signed-off-by: Bill Fischofer <bill.fischo...@linaro.org> Signed-off-by: Christophe Milard <christophe.mil...@linaro.org> --- doc/users-guide/Makefile.am | 1 + doc/users-guide/users-guide-timer.adoc | 144 +++++++++++++++++++++++++++++++++ doc/users-guide/users-guide.adoc | 2 + 3 files changed, 147 insertions(+) create mode 100644 doc/users-guide/users-guide-timer.adoc
diff --git a/doc/users-guide/Makefile.am b/doc/users-guide/Makefile.am index 2e1195e..5903392 100644 --- a/doc/users-guide/Makefile.am +++ b/doc/users-guide/Makefile.am @@ -4,6 +4,7 @@ SRC = $(top_srcdir)/doc/users-guide/users-guide.adoc \ $(top_srcdir)/doc/users-guide/users-guide-cls.adoc \ $(top_srcdir)/doc/users-guide/users-guide-packet.adoc \ $(top_srcdir)/doc/users-guide/users-guide-pktio.adoc \ + $(top_srcdir)/doc/users-guide/users-guide-timer.adoc \ $(top_srcdir)/doc/users-guide/users-guide-tm.adoc TARGET = users-guide.html IMAGES = $(top_srcdir)/doc/images/overview.svg \ diff --git a/doc/users-guide/users-guide-timer.adoc b/doc/users-guide/users-guide-timer.adoc new file mode 100644 index 0000000..9cd30de --- /dev/null +++ b/doc/users-guide/users-guide-timer.adoc @@ -0,0 +1,144 @@ +== Timers and Timeout Events +The ODP Timer APIs offer a set of functions that permit applications to react +to the passage of time, and are designed to reflect the underlying hardware +timing features found in various platforms that support ODP implementations. + +Timers are drawn from specialized pools called _timer pools_ that have their +own abstract type (`odp_timer_pool_t`). Each timer pool is a logically +independent time source with its own _resolution_ measured in nanoseconds (ns) +and a maximum number of timers that it can support. Applications can have many +timers active at the same time and can set them to use either relative or +absolute time. Associated with each timer is a queue that is to receive events +when this timer expires. This queue is created by a separate +`odp_queue_create()` call that is passed as a parameter to `odp_timer_alloc()`. + +Timeouts are specialized events of type `odp_timeout_t` that are used to +represent the expiration of timers. Timeouts are drawn from pools of type +`ODP_POOL_TIMEOUT` that are created by the standard `odp_pool_create()` API. +Timeout events are associated with timers when those timers are _set_ and are +enqueued to their timer's associated queue whenever a set timer expires. So the +effect of timer expiration is a timeout event being added to a queue and +delivered via normal ODP event scheduling. + +The following diagrams show the life cycle of timers and timeout events. +Transitions in these finite state machines are marked by the event +triggering them. Events marked in green are common to both state machines, +_i.e.,_ trigger both state machines. + +.ODP Timers lifecycle State Diagram +image::timer_fsm.svg[align="center"] + +.ODP Timeout event lifecyle State Diagram +image::timeout_fsm.svg[align="center"] + +Reminder: +On a `timer expire` event, the related timeout event is enqueued to the timer +related queue. + +Timers measure time in _ticks_ rather than nanoseconds because each timer pool +may have its own time source and associated conversion ratios. It is thus more +efficient to manipulate time in these native tick values. As a result time +measured in nanoseconds must be converted between timer-pool specific tick +values via the conversion functions `odp_timer_ns_to_tick()` and +`odp_timer_tick_to_ns()` as needed. Both of these functions take a timer pool +as an input parameter to enable the pool-specific conversion ratios to be +used. + +Associated with each timer pool is a free running tick counter that can be +sampled at any time via the `odp_timer_current_tick()` API. Timers can be set +to an absolute future tick value via `odp_timer_set_abs()` or to a future tick +value relative to the current tick via `odp_timer_set_rel()`. Implementations +may impose minimum and maximum future values supported by a given timer pool +and timer set operations will fail if the requested value is outside of the +supported range. + +Before a set timer expires, it can be canceled via the `odp_timer_cancel()` +API. A successful cancel has the same effect as if the timer were never set. +An attempted cancel will fail if the timer is not set or if it has already +expired. + +=== Timer Pool Management +To facilitate implementation of the ODP timer APIs, an additional timer API is +provided. During initialization, applications are expected to create the timer +pools they need and then call `odp_timer_pool_start()`. ODP implementations +may or may not fail further attempts to create timer pools after this API is +called. For best portability, applications should not attempt to create +further timer pools after calling `odp_timer_pool_start()`. Note that no such +restrictions exist on timeout pools, as these are just ordinary ODP pools. + +Following start, applications may allocate, set, cancel, and free timers +from their associated timer pools. During termination processing, after all +timers allocated from a timer pool have been freed, the pool itself should be +released via a call to `odp_timer_pool_destroy()`. + +=== Timeout Event Management +The purpose of ODP timers is to schedule their associated timeout events, which +are how applications actually react to the passage of time. To help with this, +several additional APIs and conventions are provided. + +Timer allocation is performed via the `odp_timer_alloc()` API: +[source,c] +----- +/** + * Allocate a timer + * + * Create a timer (allocating all necessary resources e.g. timeout event) from + * the timer pool. The user_ptr is copied to timeouts and can be retrieved + * using the odp_timeout_user_ptr() call. + * + * @param tpid Timer pool identifier + * @param queue Destination queue for timeout notifications + * @param user_ptr User defined pointer or NULL to be copied to timeouts + * + * @return Timer handle on success + * @retval ODP_TIMER_INVALID on failure and errno set. + */ +odp_timer_t odp_timer_alloc(odp_timer_pool_t tpid, + odp_queue_t queue, + void *user_ptr); +----- +Note that in addition to the timer pool id and queue, a user pointer is +provided. This is to allow context associated with the timeout to be +communicated. Upon receiving a timeout event, the application can use +the `odp_timeout_user_ptr()` API to retrieve the user pointer associated +with the timer that triggered this event. + +An worker thread receiving events that may include timeouts might be structured +as follows: +[source,c] +----- +while (1) { + ev = odp_schedule(&from, ODP_SCHED_WAIT); + + switch (odp_event_type(ev)) { + case ODP_EVENT_TIMEOUT: + odp_timeout_t timeout = odp_timeout_from_event(ev); + odp_timer_t timer = odp_timeout_timer(timeout); + void *userptr = odp_timeout_user_ptr(timeout); + uint64_t expiration = odp_timeout_tick(timeout); + + if (!odp_timeout_fresh(timeout)) { + odp_timeout_free(timeout); + continue; + } + + ...process the timeout event + break; + + ...process other event types + } +} +----- +When a worker thread receives a timeout event via `odp_schedule()`, it needs +to determine whether the event is still relevant. A timeout event that is still +relevant is said to be _fresh_ while one that is no longer relevant is said to +be _stale_. Timeouts may be stale for any number of reasons, most of which are +known only to the application itself. However, there are a few cases where the +ODP implementation may be able to assist in this determination and for those +cases the `odp_timeout_fresh()` API is provided. + +ODP defines a fresh timeout simply as one that has not been reset or +canceled since it expired. So if `odp_timeout_fresh()` returns 0 then it is +likely that the application should ignore this event, however if it returns 1 +then it remains an application responsibility to handle the event appropriate +to its needs. diff --git a/doc/users-guide/users-guide.adoc b/doc/users-guide/users-guide.adoc index 0221634..3f16608 100644 --- a/doc/users-guide/users-guide.adoc +++ b/doc/users-guide/users-guide.adoc @@ -907,6 +907,8 @@ include::users-guide-packet.adoc[] include::users-guide-pktio.adoc[] +include::users-guide-timer.adoc[] + == Cryptographic services ODP provides support for cryptographic operations required by various security -- 2.7.4 _______________________________________________ lng-odp mailing list lng-odp@lists.linaro.org https://lists.linaro.org/mailman/listinfo/lng-odp