split out qemu-timer.c

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

1 files changed, 1203 insertions, 0 deletions

diff --git a/qemu-timer.c b/qemu-timer.c
new file mode 100644
index 0000000..329d3a4
--- /dev/null
+++ b/qemu-timer.c
@@ -0,0 +1,1203 @@
+/*
+ * QEMU System Emulator
+ *
+ * Copyright (c) 2003-2008 Fabrice Bellard
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include "sysemu.h"
+#include "net.h"
+#include "monitor.h"
+#include "console.h"
+
+#include "hw/hw.h"
+
+#include <unistd.h>
+#include <fcntl.h>
+#include <time.h>
+#include <errno.h>
+#include <sys/time.h>
+#include <signal.h>
+
+#ifdef __linux__
+#include <sys/ioctl.h>
+#include <linux/rtc.h>
+/* For the benefit of older linux systems which don't supply it,
+   we use a local copy of hpet.h. */
+/* #include <linux/hpet.h> */
+#include "hpet.h"
+#endif
+
+#ifdef _WIN32
+#include <windows.h>
+#include <mmsystem.h>
+#endif
+
+#include "cpu-defs.h"
+#include "qemu-timer.h"
+#include "exec-all.h"
+
+/* Conversion factor from emulated instructions to virtual clock ticks.  */
+static int icount_time_shift;
+/* Arbitrarily pick 1MIPS as the minimum allowable speed.  */
+#define MAX_ICOUNT_SHIFT 10
+/* Compensate for varying guest execution speed.  */
+static int64_t qemu_icount_bias;
+static QEMUTimer *icount_rt_timer;
+static QEMUTimer *icount_vm_timer;
+
+
+/***********************************************************/
+/* real time host monotonic timer */
+
+
+static int64_t get_clock_realtime(void)
+{
+    struct timeval tv;
+
+    gettimeofday(&tv, NULL);
+    return tv.tv_sec * 1000000000LL + (tv.tv_usec * 1000);
+}
+
+#ifdef WIN32
+
+static int64_t clock_freq;
+
+static void init_get_clock(void)
+{
+    LARGE_INTEGER freq;
+    int ret;
+    ret = QueryPerformanceFrequency(&freq);
+    if (ret == 0) {
+        fprintf(stderr, "Could not calibrate ticks\n");
+        exit(1);
+    }
+    clock_freq = freq.QuadPart;
+}
+
+static int64_t get_clock(void)
+{
+    LARGE_INTEGER ti;
+    QueryPerformanceCounter(&ti);
+    return muldiv64(ti.QuadPart, get_ticks_per_sec(), clock_freq);
+}
+
+#else
+
+static int use_rt_clock;
+
+static void init_get_clock(void)
+{
+    use_rt_clock = 0;
+#if defined(__linux__) || (defined(__FreeBSD__) && __FreeBSD_version >= 500000) \
+    || defined(__DragonFly__) || defined(__FreeBSD_kernel__)
+    {
+        struct timespec ts;
+        if (clock_gettime(CLOCK_MONOTONIC, &ts) == 0) {
+            use_rt_clock = 1;
+        }
+    }
+#endif
+}
+
+static int64_t get_clock(void)
+{
+#if defined(__linux__) || (defined(__FreeBSD__) && __FreeBSD_version >= 500000) \
+	|| defined(__DragonFly__) || defined(__FreeBSD_kernel__)
+    if (use_rt_clock) {
+        struct timespec ts;
+        clock_gettime(CLOCK_MONOTONIC, &ts);
+        return ts.tv_sec * 1000000000LL + ts.tv_nsec;
+    } else
+#endif
+    {
+        /* XXX: using gettimeofday leads to problems if the date
+           changes, so it should be avoided. */
+        return get_clock_realtime();
+    }
+}
+#endif
+
+/* Return the virtual CPU time, based on the instruction counter.  */
+static int64_t cpu_get_icount(void)
+{
+    int64_t icount;
+    CPUState *env = cpu_single_env;;
+    icount = qemu_icount;
+    if (env) {
+        if (!can_do_io(env))
+            fprintf(stderr, "Bad clock read\n");
+        icount -= (env->icount_decr.u16.low + env->icount_extra);
+    }
+    return qemu_icount_bias + (icount << icount_time_shift);
+}
+
+/***********************************************************/
+/* guest cycle counter */
+
+typedef struct TimersState {
+    int64_t cpu_ticks_prev;
+    int64_t cpu_ticks_offset;
+    int64_t cpu_clock_offset;
+    int32_t cpu_ticks_enabled;
+    int64_t dummy;
+} TimersState;
+
+TimersState timers_state;
+
+/* return the host CPU cycle counter and handle stop/restart */
+int64_t cpu_get_ticks(void)
+{
+    if (use_icount) {
+        return cpu_get_icount();
+    }
+    if (!timers_state.cpu_ticks_enabled) {
+        return timers_state.cpu_ticks_offset;
+    } else {
+        int64_t ticks;
+        ticks = cpu_get_real_ticks();
+        if (timers_state.cpu_ticks_prev > ticks) {
+            /* Note: non increasing ticks may happen if the host uses
+               software suspend */
+            timers_state.cpu_ticks_offset += timers_state.cpu_ticks_prev - ticks;
+        }
+        timers_state.cpu_ticks_prev = ticks;
+        return ticks + timers_state.cpu_ticks_offset;
+    }
+}
+
+/* return the host CPU monotonic timer and handle stop/restart */
+static int64_t cpu_get_clock(void)
+{
+    int64_t ti;
+    if (!timers_state.cpu_ticks_enabled) {
+        return timers_state.cpu_clock_offset;
+    } else {
+        ti = get_clock();
+        return ti + timers_state.cpu_clock_offset;
+    }
+}
+
+#ifndef CONFIG_IOTHREAD
+static int64_t qemu_icount_delta(void)
+{
+    if (!use_icount) {
+        return 5000 * (int64_t) 1000000;
+    } else if (use_icount == 1) {
+        /* When not using an adaptive execution frequency
+           we tend to get badly out of sync with real time,
+           so just delay for a reasonable amount of time.  */
+        return 0;
+    } else {
+        return cpu_get_icount() - cpu_get_clock();
+    }
+}
+#endif
+
+/* enable cpu_get_ticks() */
+void cpu_enable_ticks(void)
+{
+    if (!timers_state.cpu_ticks_enabled) {
+        timers_state.cpu_ticks_offset -= cpu_get_real_ticks();
+        timers_state.cpu_clock_offset -= get_clock();
+        timers_state.cpu_ticks_enabled = 1;
+    }
+}
+
+/* disable cpu_get_ticks() : the clock is stopped. You must not call
+   cpu_get_ticks() after that.  */
+void cpu_disable_ticks(void)
+{
+    if (timers_state.cpu_ticks_enabled) {
+        timers_state.cpu_ticks_offset = cpu_get_ticks();
+        timers_state.cpu_clock_offset = cpu_get_clock();
+        timers_state.cpu_ticks_enabled = 0;
+    }
+}
+
+/***********************************************************/
+/* timers */
+
+#define QEMU_CLOCK_REALTIME 0
+#define QEMU_CLOCK_VIRTUAL  1
+#define QEMU_CLOCK_HOST     2
+
+struct QEMUClock {
+    int type;
+    int enabled;
+    /* XXX: add frequency */
+};
+
+struct QEMUTimer {
+    QEMUClock *clock;
+    int64_t expire_time;
+    QEMUTimerCB *cb;
+    void *opaque;
+    struct QEMUTimer *next;
+};
+
+struct qemu_alarm_timer {
+    char const *name;
+    int (*start)(struct qemu_alarm_timer *t);
+    void (*stop)(struct qemu_alarm_timer *t);
+    void (*rearm)(struct qemu_alarm_timer *t);
+    void *priv;
+
+    char expired;
+    char pending;
+};
+
+static struct qemu_alarm_timer *alarm_timer;
+
+int qemu_alarm_pending(void)
+{
+    return alarm_timer->pending;
+}
+
+static inline int alarm_has_dynticks(struct qemu_alarm_timer *t)
+{
+    return !!t->rearm;
+}
+
+static void qemu_rearm_alarm_timer(struct qemu_alarm_timer *t)
+{
+    if (!alarm_has_dynticks(t))
+        return;
+
+    t->rearm(t);
+}
+
+/* TODO: MIN_TIMER_REARM_US should be optimized */
+#define MIN_TIMER_REARM_US 250
+
+#ifdef _WIN32
+
+struct qemu_alarm_win32 {
+    MMRESULT timerId;
+    unsigned int period;
+} alarm_win32_data = {0, 0};
+
+static int win32_start_timer(struct qemu_alarm_timer *t);
+static void win32_stop_timer(struct qemu_alarm_timer *t);
+static void win32_rearm_timer(struct qemu_alarm_timer *t);
+
+#else
+
+static int unix_start_timer(struct qemu_alarm_timer *t);
+static void unix_stop_timer(struct qemu_alarm_timer *t);
+
+#ifdef __linux__
+
+static int dynticks_start_timer(struct qemu_alarm_timer *t);
+static void dynticks_stop_timer(struct qemu_alarm_timer *t);
+static void dynticks_rearm_timer(struct qemu_alarm_timer *t);
+
+static int hpet_start_timer(struct qemu_alarm_timer *t);
+static void hpet_stop_timer(struct qemu_alarm_timer *t);
+
+static int rtc_start_timer(struct qemu_alarm_timer *t);
+static void rtc_stop_timer(struct qemu_alarm_timer *t);
+
+#endif /* __linux__ */
+
+#endif /* _WIN32 */
+
+/* Correlation between real and virtual time is always going to be
+   fairly approximate, so ignore small variation.
+   When the guest is idle real and virtual time will be aligned in
+   the IO wait loop.  */
+#define ICOUNT_WOBBLE (get_ticks_per_sec() / 10)
+
+static void icount_adjust(void)
+{
+    int64_t cur_time;
+    int64_t cur_icount;
+    int64_t delta;
+    static int64_t last_delta;
+    /* If the VM is not running, then do nothing.  */
+    if (!vm_running)
+        return;
+
+    cur_time = cpu_get_clock();
+    cur_icount = qemu_get_clock(vm_clock);
+    delta = cur_icount - cur_time;
+    /* FIXME: This is a very crude algorithm, somewhat prone to oscillation.  */
+    if (delta > 0
+        && last_delta + ICOUNT_WOBBLE < delta * 2
+        && icount_time_shift > 0) {
+        /* The guest is getting too far ahead.  Slow time down.  */
+        icount_time_shift--;
+    }
+    if (delta < 0
+        && last_delta - ICOUNT_WOBBLE > delta * 2
+        && icount_time_shift < MAX_ICOUNT_SHIFT) {
+        /* The guest is getting too far behind.  Speed time up.  */
+        icount_time_shift++;
+    }
+    last_delta = delta;
+    qemu_icount_bias = cur_icount - (qemu_icount << icount_time_shift);
+}
+
+static void icount_adjust_rt(void * opaque)
+{
+    qemu_mod_timer(icount_rt_timer,
+                   qemu_get_clock(rt_clock) + 1000);
+    icount_adjust();
+}
+
+static void icount_adjust_vm(void * opaque)
+{
+    qemu_mod_timer(icount_vm_timer,
+                   qemu_get_clock(vm_clock) + get_ticks_per_sec() / 10);
+    icount_adjust();
+}
+
+int64_t qemu_icount_round(int64_t count)
+{
+    return (count + (1 << icount_time_shift) - 1) >> icount_time_shift;
+}
+
+static struct qemu_alarm_timer alarm_timers[] = {
+#ifndef _WIN32
+#ifdef __linux__
+    {"dynticks", dynticks_start_timer,
+     dynticks_stop_timer, dynticks_rearm_timer, NULL},
+    /* HPET - if available - is preferred */
+    {"hpet", hpet_start_timer, hpet_stop_timer, NULL, NULL},
+    /* ...otherwise try RTC */
+    {"rtc", rtc_start_timer, rtc_stop_timer, NULL, NULL},
+#endif
+    {"unix", unix_start_timer, unix_stop_timer, NULL, NULL},
+#else
+    {"dynticks", win32_start_timer,
+     win32_stop_timer, win32_rearm_timer, &alarm_win32_data},
+    {"win32", win32_start_timer,
+     win32_stop_timer, NULL, &alarm_win32_data},
+#endif
+    {NULL, }
+};
+
+static void show_available_alarms(void)
+{
+    int i;
+
+    printf("Available alarm timers, in order of precedence:\n");
+    for (i = 0; alarm_timers[i].name; i++)
+        printf("%s\n", alarm_timers[i].name);
+}
+
+void configure_alarms(char const *opt)
+{
+    int i;
+    int cur = 0;
+    int count = ARRAY_SIZE(alarm_timers) - 1;
+    char *arg;
+    char *name;
+    struct qemu_alarm_timer tmp;
+
+    if (!strcmp(opt, "?")) {
+        show_available_alarms();
+        exit(0);
+    }
+
+    arg = qemu_strdup(opt);
+
+    /* Reorder the array */
+    name = strtok(arg, ",");
+    while (name) {
+        for (i = 0; i < count && alarm_timers[i].name; i++) {
+            if (!strcmp(alarm_timers[i].name, name))
+                break;
+        }
+
+        if (i == count) {
+            fprintf(stderr, "Unknown clock %s\n", name);
+            goto next;
+        }
+
+        if (i < cur)
+            /* Ignore */
+            goto next;
+
+	/* Swap */
+        tmp = alarm_timers[i];
+        alarm_timers[i] = alarm_timers[cur];
+        alarm_timers[cur] = tmp;
+
+        cur++;
+next:
+        name = strtok(NULL, ",");
+    }
+
+    qemu_free(arg);
+
+    if (cur) {
+        /* Disable remaining timers */
+        for (i = cur; i < count; i++)
+            alarm_timers[i].name = NULL;
+    } else {
+        show_available_alarms();
+        exit(1);
+    }
+}
+
+#define QEMU_NUM_CLOCKS 3
+
+QEMUClock *rt_clock;
+QEMUClock *vm_clock;
+QEMUClock *host_clock;
+
+static QEMUTimer *active_timers[QEMU_NUM_CLOCKS];
+
+static QEMUClock *qemu_new_clock(int type)
+{
+    QEMUClock *clock;
+    clock = qemu_mallocz(sizeof(QEMUClock));
+    clock->type = type;
+    clock->enabled = 1;
+    return clock;
+}
+
+void qemu_clock_enable(QEMUClock *clock, int enabled)
+{
+    clock->enabled = enabled;
+}
+
+QEMUTimer *qemu_new_timer(QEMUClock *clock, QEMUTimerCB *cb, void *opaque)
+{
+    QEMUTimer *ts;
+
+    ts = qemu_mallocz(sizeof(QEMUTimer));
+    ts->clock = clock;
+    ts->cb = cb;
+    ts->opaque = opaque;
+    return ts;
+}
+
+void qemu_free_timer(QEMUTimer *ts)
+{
+    qemu_free(ts);
+}
+
+/* stop a timer, but do not dealloc it */
+void qemu_del_timer(QEMUTimer *ts)
+{
+    QEMUTimer **pt, *t;
+
+    /* NOTE: this code must be signal safe because
+       qemu_timer_expired() can be called from a signal. */
+    pt = &active_timers[ts->clock->type];
+    for(;;) {
+        t = *pt;
+        if (!t)
+            break;
+        if (t == ts) {
+            *pt = t->next;
+            break;
+        }
+        pt = &t->next;
+    }
+}
+
+/* modify the current timer so that it will be fired when current_time
+   >= expire_time. The corresponding callback will be called. */
+void qemu_mod_timer(QEMUTimer *ts, int64_t expire_time)
+{
+    QEMUTimer **pt, *t;
+
+    qemu_del_timer(ts);
+
+    /* add the timer in the sorted list */
+    /* NOTE: this code must be signal safe because
+       qemu_timer_expired() can be called from a signal. */
+    pt = &active_timers[ts->clock->type];
+    for(;;) {
+        t = *pt;
+        if (!t)
+            break;
+        if (t->expire_time > expire_time)
+            break;
+        pt = &t->next;
+    }
+    ts->expire_time = expire_time;
+    ts->next = *pt;
+    *pt = ts;
+
+    /* Rearm if necessary  */
+    if (pt == &active_timers[ts->clock->type]) {
+        if (!alarm_timer->pending) {
+            qemu_rearm_alarm_timer(alarm_timer);
+        }
+        /* Interrupt execution to force deadline recalculation.  */
+        if (use_icount)
+            qemu_notify_event();
+    }
+}
+
+int qemu_timer_pending(QEMUTimer *ts)
+{
+    QEMUTimer *t;
+    for(t = active_timers[ts->clock->type]; t != NULL; t = t->next) {
+        if (t == ts)
+            return 1;
+    }
+    return 0;
+}
+
+int qemu_timer_expired(QEMUTimer *timer_head, int64_t current_time)
+{
+    if (!timer_head)
+        return 0;
+    return (timer_head->expire_time <= current_time);
+}
+
+static void qemu_run_timers(QEMUClock *clock)
+{
+    QEMUTimer **ptimer_head, *ts;
+    int64_t current_time;
+   
+    if (!clock->enabled)
+        return;
+
+    current_time = qemu_get_clock (clock);
+    ptimer_head = &active_timers[clock->type];
+    for(;;) {
+        ts = *ptimer_head;
+        if (!ts || ts->expire_time > current_time)
+            break;
+        /* remove timer from the list before calling the callback */
+        *ptimer_head = ts->next;
+        ts->next = NULL;
+
+        /* run the callback (the timer list can be modified) */
+        ts->cb(ts->opaque);
+    }
+}
+
+int64_t qemu_get_clock(QEMUClock *clock)
+{
+    switch(clock->type) {
+    case QEMU_CLOCK_REALTIME:
+        return get_clock() / 1000000;
+    default:
+    case QEMU_CLOCK_VIRTUAL:
+        if (use_icount) {
+            return cpu_get_icount();
+        } else {
+            return cpu_get_clock();
+        }
+    case QEMU_CLOCK_HOST:
+        return get_clock_realtime();
+    }
+}
+
+int64_t qemu_get_clock_ns(QEMUClock *clock)
+{
+    switch(clock->type) {
+    case QEMU_CLOCK_REALTIME:
+        return get_clock();
+    default:
+    case QEMU_CLOCK_VIRTUAL:
+        if (use_icount) {
+            return cpu_get_icount();
+        } else {
+            return cpu_get_clock();
+        }
+    case QEMU_CLOCK_HOST:
+        return get_clock_realtime();
+    }
+}
+
+void init_clocks(void)
+{
+    init_get_clock();
+    rt_clock = qemu_new_clock(QEMU_CLOCK_REALTIME);
+    vm_clock = qemu_new_clock(QEMU_CLOCK_VIRTUAL);
+    host_clock = qemu_new_clock(QEMU_CLOCK_HOST);
+
+    rtc_clock = host_clock;
+}
+
+/* save a timer */
+void qemu_put_timer(QEMUFile *f, QEMUTimer *ts)
+{
+    uint64_t expire_time;
+
+    if (qemu_timer_pending(ts)) {
+        expire_time = ts->expire_time;
+    } else {
+        expire_time = -1;
+    }
+    qemu_put_be64(f, expire_time);
+}
+
+void qemu_get_timer(QEMUFile *f, QEMUTimer *ts)
+{
+    uint64_t expire_time;
+
+    expire_time = qemu_get_be64(f);
+    if (expire_time != -1) {
+        qemu_mod_timer(ts, expire_time);
+    } else {
+        qemu_del_timer(ts);
+    }
+}
+
+static const VMStateDescription vmstate_timers = {
+    .name = "timer",
+    .version_id = 2,
+    .minimum_version_id = 1,
+    .minimum_version_id_old = 1,
+    .fields      = (VMStateField []) {
+        VMSTATE_INT64(cpu_ticks_offset, TimersState),
+        VMSTATE_INT64(dummy, TimersState),
+        VMSTATE_INT64_V(cpu_clock_offset, TimersState, 2),
+        VMSTATE_END_OF_LIST()
+    }
+};
+
+void configure_icount(const char *option)
+{
+    vmstate_register(0, &vmstate_timers, &timers_state);
+    if (!option)
+        return;
+
+    if (strcmp(option, "auto") != 0) {
+        icount_time_shift = strtol(option, NULL, 0);
+        use_icount = 1;
+        return;
+    }
+
+    use_icount = 2;
+
+    /* 125MIPS seems a reasonable initial guess at the guest speed.
+       It will be corrected fairly quickly anyway.  */
+    icount_time_shift = 3;
+
+    /* Have both realtime and virtual time triggers for speed adjustment.
+       The realtime trigger catches emulated time passing too slowly,
+       the virtual time trigger catches emulated time passing too fast.
+       Realtime triggers occur even when idle, so use them less frequently
+       than VM triggers.  */
+    icount_rt_timer = qemu_new_timer(rt_clock, icount_adjust_rt, NULL);
+    qemu_mod_timer(icount_rt_timer,
+                   qemu_get_clock(rt_clock) + 1000);
+    icount_vm_timer = qemu_new_timer(vm_clock, icount_adjust_vm, NULL);
+    qemu_mod_timer(icount_vm_timer,
+                   qemu_get_clock(vm_clock) + get_ticks_per_sec() / 10);
+}
+
+void qemu_run_all_timers(void)
+{
+    /* rearm timer, if not periodic */
+    if (alarm_timer->expired) {
+        alarm_timer->expired = 0;
+        qemu_rearm_alarm_timer(alarm_timer);
+    }
+
+    alarm_timer->pending = 0;
+
+    /* vm time timers */
+    if (vm_running) {
+        qemu_run_timers(vm_clock);
+    }
+
+    qemu_run_timers(rt_clock);
+    qemu_run_timers(host_clock);
+}
+
+#ifdef _WIN32
+static void CALLBACK host_alarm_handler(UINT uTimerID, UINT uMsg,
+                                        DWORD_PTR dwUser, DWORD_PTR dw1,
+                                        DWORD_PTR dw2)
+#else
+static void host_alarm_handler(int host_signum)
+#endif
+{
+    struct qemu_alarm_timer *t = alarm_timer;
+    if (!t)
+	return;
+
+#if 0
+#define DISP_FREQ 1000
+    {
+        static int64_t delta_min = INT64_MAX;
+        static int64_t delta_max, delta_cum, last_clock, delta, ti;
+        static int count;
+        ti = qemu_get_clock(vm_clock);
+        if (last_clock != 0) {
+            delta = ti - last_clock;
+            if (delta < delta_min)
+                delta_min = delta;
+            if (delta > delta_max)
+                delta_max = delta;
+            delta_cum += delta;
+            if (++count == DISP_FREQ) {
+                printf("timer: min=%" PRId64 " us max=%" PRId64 " us avg=%" PRId64 " us avg_freq=%0.3f Hz\n",
+                       muldiv64(delta_min, 1000000, get_ticks_per_sec()),
+                       muldiv64(delta_max, 1000000, get_ticks_per_sec()),
+                       muldiv64(delta_cum, 1000000 / DISP_FREQ, get_ticks_per_sec()),
+                       (double)get_ticks_per_sec() / ((double)delta_cum / DISP_FREQ));
+                count = 0;
+                delta_min = INT64_MAX;
+                delta_max = 0;
+                delta_cum = 0;
+            }
+        }
+        last_clock = ti;
+    }
+#endif
+    if (alarm_has_dynticks(t) ||
+        (!use_icount &&
+            qemu_timer_expired(active_timers[QEMU_CLOCK_VIRTUAL],
+                               qemu_get_clock(vm_clock))) ||
+        qemu_timer_expired(active_timers[QEMU_CLOCK_REALTIME],
+                           qemu_get_clock(rt_clock)) ||
+        qemu_timer_expired(active_timers[QEMU_CLOCK_HOST],
+                           qemu_get_clock(host_clock))) {
+
+        t->expired = alarm_has_dynticks(t);
+        t->pending = 1;
+        qemu_notify_event();
+    }
+}
+
+int64_t qemu_next_deadline(void)
+{
+    /* To avoid problems with overflow limit this to 2^32.  */
+    int64_t delta = INT32_MAX;
+
+    if (active_timers[QEMU_CLOCK_VIRTUAL]) {
+        delta = active_timers[QEMU_CLOCK_VIRTUAL]->expire_time -
+                     qemu_get_clock(vm_clock);
+    }
+    if (active_timers[QEMU_CLOCK_HOST]) {
+        int64_t hdelta = active_timers[QEMU_CLOCK_HOST]->expire_time -
+                 qemu_get_clock(host_clock);
+        if (hdelta < delta)
+            delta = hdelta;
+    }
+
+    if (delta < 0)
+        delta = 0;
+
+    return delta;
+}
+
+#ifndef _WIN32
+
+#if defined(__linux__)
+
+#define RTC_FREQ 1024
+
+static uint64_t qemu_next_deadline_dyntick(void)
+{
+    int64_t delta;
+    int64_t rtdelta;
+
+    if (use_icount)
+        delta = INT32_MAX;
+    else
+        delta = (qemu_next_deadline() + 999) / 1000;
+
+    if (active_timers[QEMU_CLOCK_REALTIME]) {
+        rtdelta = (active_timers[QEMU_CLOCK_REALTIME]->expire_time -
+                 qemu_get_clock(rt_clock))*1000;
+        if (rtdelta < delta)
+            delta = rtdelta;
+    }
+
+    if (delta < MIN_TIMER_REARM_US)
+        delta = MIN_TIMER_REARM_US;
+
+    return delta;
+}
+
+static void enable_sigio_timer(int fd)
+{
+    struct sigaction act;
+
+    /* timer signal */
+    sigfillset(&act.sa_mask);
+    act.sa_flags = 0;
+    act.sa_handler = host_alarm_handler;
+
+    sigaction(SIGIO, &act, NULL);
+    fcntl_setfl(fd, O_ASYNC);
+    fcntl(fd, F_SETOWN, getpid());
+}
+
+static int hpet_start_timer(struct qemu_alarm_timer *t)
+{
+    struct hpet_info info;
+    int r, fd;
+
+    fd = qemu_open("/dev/hpet", O_RDONLY);
+    if (fd < 0)
+        return -1;
+
+    /* Set frequency */
+    r = ioctl(fd, HPET_IRQFREQ, RTC_FREQ);
+    if (r < 0) {
+        fprintf(stderr, "Could not configure '/dev/hpet' to have a 1024Hz timer. This is not a fatal\n"
+                "error, but for better emulation accuracy type:\n"
+                "'echo 1024 > /proc/sys/dev/hpet/max-user-freq' as root.\n");
+        goto fail;
+    }
+
+    /* Check capabilities */
+    r = ioctl(fd, HPET_INFO, &info);
+    if (r < 0)
+        goto fail;
+
+    /* Enable periodic mode */
+    r = ioctl(fd, HPET_EPI, 0);
+    if (info.hi_flags && (r < 0))
+        goto fail;
+
+    /* Enable interrupt */
+    r = ioctl(fd, HPET_IE_ON, 0);
+    if (r < 0)
+        goto fail;
+
+    enable_sigio_timer(fd);
+    t->priv = (void *)(long)fd;
+
+    return 0;
+fail:
+    close(fd);
+    return -1;
+}
+
+static void hpet_stop_timer(struct qemu_alarm_timer *t)
+{
+    int fd = (long)t->priv;
+
+    close(fd);
+}
+
+static int rtc_start_timer(struct qemu_alarm_timer *t)
+{
+    int rtc_fd;
+    unsigned long current_rtc_freq = 0;
+
+    TFR(rtc_fd = qemu_open("/dev/rtc", O_RDONLY));
+    if (rtc_fd < 0)
+        return -1;
+    ioctl(rtc_fd, RTC_IRQP_READ, &current_rtc_freq);
+    if (current_rtc_freq != RTC_FREQ &&
+        ioctl(rtc_fd, RTC_IRQP_SET, RTC_FREQ) < 0) {
+        fprintf(stderr, "Could not configure '/dev/rtc' to have a 1024 Hz timer. This is not a fatal\n"
+                "error, but for better emulation accuracy either use a 2.6 host Linux kernel or\n"
+                "type 'echo 1024 > /proc/sys/dev/rtc/max-user-freq' as root.\n");
+        goto fail;
+    }
+    if (ioctl(rtc_fd, RTC_PIE_ON, 0) < 0) {
+    fail:
+        close(rtc_fd);
+        return -1;
+    }
+
+    enable_sigio_timer(rtc_fd);
+
+    t->priv = (void *)(long)rtc_fd;
+
+    return 0;
+}
+
+static void rtc_stop_timer(struct qemu_alarm_timer *t)
+{
+    int rtc_fd = (long)t->priv;
+
+    close(rtc_fd);
+}
+
+static int dynticks_start_timer(struct qemu_alarm_timer *t)
+{
+    struct sigevent ev;
+    timer_t host_timer;
+    struct sigaction act;
+
+    sigfillset(&act.sa_mask);
+    act.sa_flags = 0;
+    act.sa_handler = host_alarm_handler;
+
+    sigaction(SIGALRM, &act, NULL);
+
+    /* 
+     * Initialize ev struct to 0 to avoid valgrind complaining
+     * about uninitialized data in timer_create call
+     */
+    memset(&ev, 0, sizeof(ev));
+    ev.sigev_value.sival_int = 0;
+    ev.sigev_notify = SIGEV_SIGNAL;
+    ev.sigev_signo = SIGALRM;
+
+    if (timer_create(CLOCK_REALTIME, &ev, &host_timer)) {
+        perror("timer_create");
+
+        /* disable dynticks */
+        fprintf(stderr, "Dynamic Ticks disabled\n");
+
+        return -1;
+    }
+
+    t->priv = (void *)(long)host_timer;
+
+    return 0;
+}
+
+static void dynticks_stop_timer(struct qemu_alarm_timer *t)
+{
+    timer_t host_timer = (timer_t)(long)t->priv;
+
+    timer_delete(host_timer);
+}
+
+static void dynticks_rearm_timer(struct qemu_alarm_timer *t)
+{
+    timer_t host_timer = (timer_t)(long)t->priv;
+    struct itimerspec timeout;
+    int64_t nearest_delta_us = INT64_MAX;
+    int64_t current_us;
+
+    assert(alarm_has_dynticks(t));
+    if (!active_timers[QEMU_CLOCK_REALTIME] &&
+        !active_timers[QEMU_CLOCK_VIRTUAL] &&
+        !active_timers[QEMU_CLOCK_HOST])
+        return;
+
+    nearest_delta_us = qemu_next_deadline_dyntick();
+
+    /* check whether a timer is already running */
+    if (timer_gettime(host_timer, &timeout)) {
+        perror("gettime");
+        fprintf(stderr, "Internal timer error: aborting\n");
+        exit(1);
+    }
+    current_us = timeout.it_value.tv_sec * 1000000 + timeout.it_value.tv_nsec/1000;
+    if (current_us && current_us <= nearest_delta_us)
+        return;
+
+    timeout.it_interval.tv_sec = 0;
+    timeout.it_interval.tv_nsec = 0; /* 0 for one-shot timer */
+    timeout.it_value.tv_sec =  nearest_delta_us / 1000000;
+    timeout.it_value.tv_nsec = (nearest_delta_us % 1000000) * 1000;
+    if (timer_settime(host_timer, 0 /* RELATIVE */, &timeout, NULL)) {
+        perror("settime");
+        fprintf(stderr, "Internal timer error: aborting\n");
+        exit(1);
+    }
+}
+
+#endif /* defined(__linux__) */
+
+static int unix_start_timer(struct qemu_alarm_timer *t)
+{
+    struct sigaction act;
+    struct itimerval itv;
+    int err;
+
+    /* timer signal */
+    sigfillset(&act.sa_mask);
+    act.sa_flags = 0;
+    act.sa_handler = host_alarm_handler;
+
+    sigaction(SIGALRM, &act, NULL);
+
+    itv.it_interval.tv_sec = 0;
+    /* for i386 kernel 2.6 to get 1 ms */
+    itv.it_interval.tv_usec = 999;
+    itv.it_value.tv_sec = 0;
+    itv.it_value.tv_usec = 10 * 1000;
+
+    err = setitimer(ITIMER_REAL, &itv, NULL);
+    if (err)
+        return -1;
+
+    return 0;
+}
+
+static void unix_stop_timer(struct qemu_alarm_timer *t)
+{
+    struct itimerval itv;
+
+    memset(&itv, 0, sizeof(itv));
+    setitimer(ITIMER_REAL, &itv, NULL);
+}
+
+#endif /* !defined(_WIN32) */
+
+
+#ifdef _WIN32
+
+static int win32_start_timer(struct qemu_alarm_timer *t)
+{
+    TIMECAPS tc;
+    struct qemu_alarm_win32 *data = t->priv;
+    UINT flags;
+
+    memset(&tc, 0, sizeof(tc));
+    timeGetDevCaps(&tc, sizeof(tc));
+
+    data->period = tc.wPeriodMin;
+    timeBeginPeriod(data->period);
+
+    flags = TIME_CALLBACK_FUNCTION;
+    if (alarm_has_dynticks(t))
+        flags |= TIME_ONESHOT;
+    else
+        flags |= TIME_PERIODIC;
+
+    data->timerId = timeSetEvent(1,         // interval (ms)
+                        data->period,       // resolution
+                        host_alarm_handler, // function
+                        (DWORD)t,           // parameter
+                        flags);
+
+    if (!data->timerId) {
+        fprintf(stderr, "Failed to initialize win32 alarm timer: %ld\n",
+                GetLastError());
+        timeEndPeriod(data->period);
+        return -1;
+    }
+
+    return 0;
+}
+
+static void win32_stop_timer(struct qemu_alarm_timer *t)
+{
+    struct qemu_alarm_win32 *data = t->priv;
+
+    timeKillEvent(data->timerId);
+    timeEndPeriod(data->period);
+}
+
+static void win32_rearm_timer(struct qemu_alarm_timer *t)
+{
+    struct qemu_alarm_win32 *data = t->priv;
+
+    assert(alarm_has_dynticks(t));
+    if (!active_timers[QEMU_CLOCK_REALTIME] &&
+        !active_timers[QEMU_CLOCK_VIRTUAL] &&
+        !active_timers[QEMU_CLOCK_HOST])
+        return;
+
+    timeKillEvent(data->timerId);
+
+    data->timerId = timeSetEvent(1,
+                        data->period,
+                        host_alarm_handler,
+                        (DWORD)t,
+                        TIME_ONESHOT | TIME_CALLBACK_FUNCTION);
+
+    if (!data->timerId) {
+        fprintf(stderr, "Failed to re-arm win32 alarm timer %ld\n",
+                GetLastError());
+
+        timeEndPeriod(data->period);
+        exit(1);
+    }
+}
+
+#endif /* _WIN32 */
+
+static void alarm_timer_on_change_state_rearm(void *opaque, int running, int reason)
+{
+    if (running)
+        qemu_rearm_alarm_timer((struct qemu_alarm_timer *) opaque);
+}
+
+int init_timer_alarm(void)
+{
+    struct qemu_alarm_timer *t = NULL;
+    int i, err = -1;
+
+    for (i = 0; alarm_timers[i].name; i++) {
+        t = &alarm_timers[i];
+
+        err = t->start(t);
+        if (!err)
+            break;
+    }
+
+    if (err) {
+        err = -ENOENT;
+        goto fail;
+    }
+
+    /* first event is at time 0 */
+    t->pending = 1;
+    alarm_timer = t;
+    qemu_add_vm_change_state_handler(alarm_timer_on_change_state_rearm, t);
+
+    return 0;
+
+fail:
+    return err;
+}
+
+void quit_timers(void)
+{
+    struct qemu_alarm_timer *t = alarm_timer;
+    alarm_timer = NULL;
+    t->stop(t);
+}
+
+int qemu_calculate_timeout(void)
+{
+#ifndef CONFIG_IOTHREAD
+    int timeout;
+
+    if (!vm_running)
+        timeout = 5000;
+    else {
+     /* XXX: use timeout computed from timers */
+        int64_t add;
+        int64_t delta;
+        /* Advance virtual time to the next event.  */
+	delta = qemu_icount_delta();
+        if (delta > 0) {
+            /* If virtual time is ahead of real time then just
+               wait for IO.  */
+            timeout = (delta + 999999) / 1000000;
+        } else {
+            /* Wait for either IO to occur or the next
+               timer event.  */
+            add = qemu_next_deadline();
+            /* We advance the timer before checking for IO.
+               Limit the amount we advance so that early IO
+               activity won't get the guest too far ahead.  */
+            if (add > 10000000)
+                add = 10000000;
+            delta += add;
+            qemu_icount += qemu_icount_round (add);
+            timeout = delta / 1000000;
+            if (timeout < 0)
+                timeout = 0;
+        }
+    }
+
+    return timeout;
+#else /* CONFIG_IOTHREAD */
+    return 1000;
+#endif
+}
+