Manual Pages  — EVENTTIMERS

eventtimers – kernel event timers subsystem

SYNOPSIS DESCRIPTION DRIVER API CONSUMER API SEE ALSO AUTHORS

#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);

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 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.

Alexander Motin <Mt mav@FreeBSD.org>