pmon/sys/kern/kern_timeout.c

/*
 * Copyright (c) 2001 Thomas Nordin <nordin@openbsd.org>
 * Copyright (c) 2000-2001 Artur Grabowski <art@openbsd.org>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
 * AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
 * THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL  DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
 * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
 * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/lock.h>
#include <sys/timeout.h>
#include <sys/kernel.h>
#include <sys/queue.h>			/* _Q_INVALIDATE */

/*
 * Timeouts are kept in a hierarchical timing wheel. The to_time is the value
 * of the global variable "ticks" when the timeout should be called. There are
 * four levels with 256 buckets each. See 'Scheme 7' in
 * "Hashed and Hierarchical Timing Wheels: Efficient Data Structures for
 * Implementing a Timer Facility" by George Varghese and Tony Lauck.
 */
#define BUCKETS 1024
#define WHEELSIZE 256
#define WHEELMASK 255
#define WHEELBITS 8

struct circq timeout_wheel[BUCKETS];	/* Queues of timeouts */
struct circq timeout_todo;		/* Worklist */

#define MASKWHEEL(wheel, time) (((time) >> ((wheel)*WHEELBITS)) & WHEELMASK)

#define BUCKET(rel, abs)						\
    (timeout_wheel[							\
	((rel) <= (1 << (2*WHEELBITS)))				\
	    ? ((rel) <= (1 << WHEELBITS))				\
		? MASKWHEEL(0, (abs))					\
		: MASKWHEEL(1, (abs)) + WHEELSIZE			\
	    : ((rel) <= (1 << (3*WHEELBITS)))				\
		? MASKWHEEL(2, (abs)) + 2*WHEELSIZE			\
		: MASKWHEEL(3, (abs)) + 3*WHEELSIZE])

#define MOVEBUCKET(wheel, time)						\
    CIRCQ_APPEND(&timeout_todo,						\
        &timeout_wheel[MASKWHEEL((wheel), (time)) + (wheel)*WHEELSIZE])

/*
 * All wheels are locked with the same mutex.
 *
 * We need locking since the timeouts are manipulated from hardclock that's
 * not behind the big lock.
 */

/*
 * Circular queue definitions.
 */

#define CIRCQ_INIT(elem) do {                   \
        (elem)->next = (elem);                  \
        (elem)->prev = (elem);                  \
} while (0)

#define CIRCQ_INSERT(elem, list) do {           \
        (elem)->prev = (list)->prev;            \
        (elem)->next = (list);                  \
        (list)->prev->next = (elem);            \
        (list)->prev = (elem);                  \
} while (0)

#define CIRCQ_APPEND(fst, snd) do {             \
        if (!CIRCQ_EMPTY(snd)) {                \
                (fst)->prev->next = (snd)->next;\
                (snd)->next->prev = (fst)->prev;\
                (snd)->prev->next = (fst);      \
                (fst)->prev = (snd)->prev;      \
                CIRCQ_INIT(snd);                \
        }                                       \
} while (0)

#define CIRCQ_REMOVE(elem) do {                 \
        (elem)->next->prev = (elem)->prev;      \
        (elem)->prev->next = (elem)->next;      \
	_Q_INVALIDATE((elem)->prev);		\
	_Q_INVALIDATE((elem)->next);		\
} while (0)

#define CIRCQ_FIRST(elem) ((elem)->next)

#define CIRCQ_EMPTY(elem) (CIRCQ_FIRST(elem) == (elem))

/*
 * Some of the "math" in here is a bit tricky.
 *
 * We have to beware of wrapping ints.
 * We use the fact that any element added to the queue must be added with a
 * positive time. That means that any element `to' on the queue cannot be
 * scheduled to timeout further in time than INT_MAX, but to->to_time can
 * be positive or negative so comparing it with anything is dangerous.
 * The only way we can use the to->to_time value in any predictable way
 * is when we calculate how far in the future `to' will timeout -
 * "to->to_time - ticks". The result will always be positive for future
 * timeouts and 0 or negative for due timeouts.
 */
extern int ticks;		/* XXX - move to sys/X.h */

void
timeout_add(struct timeout *new, int to_ticks)
{
	int old_time;

#ifdef DIAGNOSTIC
	if (!(new->to_flags & TIMEOUT_INITIALIZED))
		panic("timeout_add: not initialized");
	if (to_ticks < 0)
		panic("timeout_add: to_ticks (%d) < 0", to_ticks);
#endif

	/* Initialize the time here, it won't change. */
	old_time = new->to_time;
	new->to_time = to_ticks + ticks;
	new->to_flags &= ~TIMEOUT_TRIGGERED;

	/*
	 * If this timeout already is scheduled and now is moved
	 * earlier, reschedule it now. Otherwise leave it in place
	 * and let it be rescheduled later.
	 */
	if (new->to_flags & TIMEOUT_ONQUEUE) {
		if (new->to_time - ticks < old_time - ticks) {
			CIRCQ_REMOVE(&new->to_list);
			CIRCQ_INSERT(&new->to_list, &timeout_todo);
		}
	} else {
		new->to_flags |= TIMEOUT_ONQUEUE;
		CIRCQ_INSERT(&new->to_list, &timeout_todo);
	}
}

void
timeout_del(struct timeout *to)
{
	if (to->to_flags & TIMEOUT_ONQUEUE) {
		CIRCQ_REMOVE(&to->to_list);
		to->to_flags &= ~TIMEOUT_ONQUEUE;
	}
	to->to_flags &= ~TIMEOUT_TRIGGERED;
}