EVENTTIMERS(9) FreeBSD Kernel Developer's Manual EVENTTIMERS(9)
NAME
eventtimers - kernel event timers subsystem
SYNOPSIS
#include <sys/timeet.h>
struct eventtimer;
typedef int et_start_t(struct eventtimer *et,
sbintime_t first, sbintime_t period);
typedef int et_stop_t(struct eventtimer *et);
typedef void et_event_cb_t(struct eventtimer *et, void *arg);
typedef int et_deregister_cb_t(struct eventtimer *et, void *arg);
struct eventtimer {
SLIST_ENTRY(eventtimer) et_all;
char *et_name;
int et_flags;
#define ET_FLAGS_PERIODIC 1
#define ET_FLAGS_ONESHOT 2
#define ET_FLAGS_PERCPU 4
#define ET_FLAGS_C3STOP 8
#define ET_FLAGS_POW2DIV 16
int et_quality;
int et_active;
uint64_t et_frequency;
sbintime_t et_min_period;
sbintime_t et_max_period;
et_start_t *et_start;
et_stop_t *et_stop;
et_event_cb_t *et_event_cb;
et_deregister_cb_t *et_deregister_cb;
void *et_arg;
void *et_priv;
struct sysctl_oid *et_sysctl;
};
int
et_register(struct eventtimer *et);
int
et_deregister(struct eventtimer *et);
void
et_change_frequency(struct eventtimer *et, uint64_t newfreq);
ET_LOCK();
ET_UNLOCK();
struct eventtimer *
et_find(const char *name, int check, int want);
int
et_init(struct eventtimer *et, et_event_cb_t *event,
et_deregister_cb_t *deregister, void *arg);
int
et_start(struct eventtimer *et, sbintime_t first, sbintime_t period);
int
et_stop(struct eventtimer *et);
int
et_ban(struct eventtimer *et);
int
et_free(struct eventtimer *et);
DESCRIPTION
Event timers are responsible for generating interrupts at specified time
or periodically, to run different time-based events. Subsystem consists
of three main parts:
Drivers Manage hardware to generate requested time events.
Consumers sys/kern/kern_clocksource.c uses event timers to supply kernel
with hardclock(), statclock() and profclock() time events.
Glue code sys/sys/timeet.h, sys/kern/kern_et.c provide APIs for event
timer drivers and consumers.
DRIVER API
Driver API is built around eventtimer structure. To register its
functionality driver allocates that structure and calls et_register().
Driver should fill following fields there:
et_name Unique name of the event timer for management purposes.
et_flags Set of flags, describing timer capabilities:
ET_FLAGS_PERIODIC Periodic mode supported.
ET_FLAGS_ONESHOT One-shot mode supported.
ET_FLAGS_PERCPU Timer is per-CPU.
ET_FLAGS_C3STOP Timer may stop in CPU sleep state.
ET_FLAGS_POW2DIV Timer supports only 2^n divisors.
et_quality Abstract value to certify whether this timecounter is
better than the others. Higher value means better.
et_frequency Timer oscillator's base frequency, if applicable and known.
Used by consumers to predict set of possible frequencies
that could be obtained by dividing it. Should be zero if
not applicable or unknown.
et_min_period, et_max_period
Minimal and maximal reliably programmable time periods.
et_start Driver's timer start function pointer.
et_stop Driver's timer stop function pointer.
et_priv Driver's private data storage.
After the event timer functionality is registered, it is controlled via
et_start and et_stop methods. et_start method is called to start the
specified event timer. The last two arguments are used to specify time
when events should be generated. first argument specifies time period
before the first event generated. In periodic mode NULL value specifies
that first period is equal to the period argument value. period argument
specifies the time period between following events for the periodic mode.
The NULL value there specifies the one-shot mode. At least one of these
two arguments should be not NULL. When event time arrive, driver should
call et_event_cb callback function, passing et_arg as the second
argument. et_stop method is called to stop the specified event timer.
For the per-CPU event timers et_start and et_stop methods control timers
associated with the current CPU.
Driver may deregister its functionality by calling et_deregister().
If the frequency of the clock hardware can change while it is running
(for example, during power-saving modes), the driver must call
et_change_frequency() on each change. If the given event timer is the
active timer, et_change_frequency() stops the timer on all CPUs, updates
et->frequency, then restarts the timer on all CPUs so that all current
events are rescheduled using the new frequency. If the given timer is
not currently active, et_change_frequency() simply updates et->frequency.
CONSUMER API
et_find() allows consumer to find available event timer, optionally
matching specific name and/or capability flags. Consumer may read
returned eventtimer structure, but should not modify it. When wanted
event timer is found, et_init() should be called for it, submitting event
and optionally deregister callbacks functions, and the opaque argument
arg. That argument will be passed as argument to the callbacks. Event
callback function will be called on scheduled time events. It is called
from the hardware interrupt context, so no sleep is permitted there.
Deregister callback function may be called to report consumer that the
event timer functionality is no longer available. On this call, consumer
should stop using event timer before the return.
After the timer is found and initialized, it can be controlled via
et_start() and et_stop(). The arguments are the same as described in
driver API. Per-CPU event timers can be controlled only from specific
CPUs.
et_ban() allows consumer to mark event timer as broken via clearing both
one-shot and periodic capability flags, if it was somehow detected.
et_free() is the opposite to et_init(). It releases the event timer for
other consumers use.
ET_LOCK() and ET_UNLOCK() macros should be used to manage mutex(9) lock
around et_find(), et_init() and et_free() calls to serialize access to
the list of the registered event timers and the pointers returned by
et_find(). et_start() and et_stop() calls should be serialized in
consumer's internal way to avoid concurrent timer hardware access.
SEE ALSO
eventtimers(4)
AUTHORS
Alexander Motin <mav@FreeBSD.org>
FreeBSD 13.1-RELEASE-p6 April 2, 2014 FreeBSD 13.1-RELEASE-p6
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