table of contents
EVENTTIMERS(9) | 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
() andprofclock
() 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 callset_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.
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⟩April 2, 2014 | Debian |