eventtimers (9)

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Copyright (c) 2011-2013 Alexander Motin <mav@FreeBSD.org>
All rights reserved.

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modification, are permitted provided that the following conditions
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1. Redistributions of source code must retain the above copyright
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   ...

(The comments found at the beginning of the groff file "man9/eventtimers.9freebsd".)

NAME

eventtimers - kernel event timers subsystem

SYNOPSIS

In 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;
};

Ft int Fn et_register struct eventtimer *et Ft int Fn et_deregister struct eventtimer *et Ft void Fn et_change_frequency struct eventtimer *et uint64_t newfreq Fn ET_LOCK Fn ET_UNLOCK Ft struct eventtimer * Fn et_find const char *name int check int want Ft int Fn et_init struct eventtimer *et et_event_cb_t *event et_deregister_cb_t *deregister void *arg Ft int Fn et_start struct eventtimer *et sbintime_t first sbintime_t period Ft int Fn et_stop struct eventtimer *et Ft int Fn et_ban struct eventtimer *et Ft int Fn 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 Fn hardclock , Fn statclock and Fn 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 Fn 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 Fn 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 Fn et_change_frequency on each change. If the given event timer is the active timer, Fn 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, Fn et_change_frequency simply updates et->frequency

CONSUMER API

Fn 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, Fn 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 Fn et_start and Fn et_stop . The arguments are the same as described in driver API. Per-CPU event timers can be controlled only from specific CPUs.

Fn et_ban allows consumer to mark event timer as broken via clearing both one-shot and periodic capability flags, if it was somehow detected. Fn et_free is the opposite to Fn et_init . It releases the event timer for other consumers use.

Fn ET_LOCK and Fn ET_UNLOCK macros should be used to manage mutex(9) lock around Fn et_find , Fn et_init and Fn et_free calls to serialize access to the list of the registered event timers and the pointers returned by Fn et_find . Fn et_start and Fn et_stop calls should be serialized in consumer's internal way to avoid concurrent timer hardware access.

SEE ALSO

eventtimers(4)

AUTHORS

An Alexander Motin Aq mav@FreeBSD.org