[PATCH 4/4] Add support for dynamic ticks.

Luca Tettamanti
2007-08-17T23:11:53Z

[-- Attachment #1: clock-dyn --]
[-- Type: text/plain, Size: 7933 bytes --]

If DYNAMIC_TICKS is defined qemu does not attepmt to generate SIGALRM at a
constant rate. Rather, the system timer is set to generate SIGALRM only
when it is needed. DYNAMIC_TICKS reduces the number of SIGALRMs sent to
idle dynamic-ticked guests.
Original patch from Dan Kenigsberg <dank-atKUWr5tajBWk0Htik3J/w@public.gmane.org>

Signed-off-by: Luca Tettamanti <kronos.it-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>

---
configure | 5 ++
vl.c | 149 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++---
2 files changed, 148 insertions(+), 6 deletions(-)

Index: qemu/vl.c
===================================================================
--- qemu.orig/vl.c 2007-08-17 17:45:00.000000000 +0200
+++ qemu/vl.c 2007-08-18 00:38:03.000000000 +0200
@@ -784,12 +784,42 @@

struct qemu_alarm_timer {
char const *name;
+ unsigned int flags;

int (*start)(struct qemu_alarm_timer *t);
void (*stop)(struct qemu_alarm_timer *t);
+ void (*rearm)(struct qemu_alarm_timer *t);
void *priv;
};

+#define ALARM_FLAG_DYNTICKS 0x1
+
+#ifdef DYNAMIC_TICKS
+
+static inline int alarm_has_dynticks(struct qemu_alarm_timer *t)
+{
+ return t->flags & ALARM_FLAG_DYNTICKS;
+}
+
+static void qemu_rearm_alarm_timer(struct qemu_alarm_timer *t) {
+ if (!alarm_has_dynticks(t))
+ return;
+
+ t->rearm(t);
+}
+
+#else /* DYNAMIC_TICKS */
+
+static inline int alarm_has_dynticks(struct qemu_alarm_timer *t)
+{
+ return 0;
+}
+
+static void qemu_rearm_alarm_timer(void) {
+}
+
+#endif /* DYNAMIC_TICKS */
+
static struct qemu_alarm_timer *alarm_timer;

#ifdef _WIN32
@@ -808,6 +838,14 @@
static int unix_start_timer(struct qemu_alarm_timer *t);
static void unix_stop_timer(struct qemu_alarm_timer *t);

+#ifdef DYNAMIC_TICKS
+
+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);
+
+#endif
+
#ifdef __linux__

static int hpet_start_timer(struct qemu_alarm_timer *t);
@@ -821,16 +859,19 @@
#endif /* _WIN32 */

static struct qemu_alarm_timer alarm_timers[] = {
+#ifndef _WIN32
+#ifdef DYNAMIC_TICKS
+ {"dynticks", ALARM_FLAG_DYNTICKS, dynticks_start_timer, dynticks_stop_timer, dynticks_rearm_timer, NULL},
+#endif
#ifdef __linux__
/* HPET - if available - is preferred */
- {"hpet", hpet_start_timer, hpet_stop_timer, NULL},
+ {"hpet", 0, hpet_start_timer, hpet_stop_timer, NULL, NULL},
/* ...otherwise try RTC */
- {"rtc", rtc_start_timer, rtc_stop_timer, NULL},
+ {"rtc", 0, rtc_start_timer, rtc_stop_timer, NULL, NULL},
#endif
-#ifndef _WIN32
- {"unix", unix_start_timer, unix_stop_timer, NULL},
+ {"unix", 0, unix_start_timer, unix_stop_timer, NULL, NULL},
#else
- {"win32", win32_start_timer, win32_stop_timer, &alarm_win32_data},
+ {"win32", 0, win32_start_timer, win32_stop_timer, NULL, &alarm_win32_data},
#endif
{NULL, }
};
@@ -949,6 +990,8 @@
}
pt = &t->next;
}
+
+ qemu_rearm_alarm_timer(alarm_timer);
}

/* modify the current timer so that it will be fired when current_time
@@ -1008,6 +1051,7 @@
/* run the callback (the timer list can be modified) */
ts->cb(ts->opaque);
}
+ qemu_rearm_alarm_timer(alarm_timer);
}

int64_t qemu_get_clock(QEMUClock *clock)
@@ -1115,7 +1159,8 @@
last_clock = ti;
}
#endif
- if (qemu_timer_expired(active_timers[QEMU_TIMER_VIRTUAL],
+ if (alarm_has_dynticks(alarm_timer) ||
+ qemu_timer_expired(active_timers[QEMU_TIMER_VIRTUAL],
qemu_get_clock(vm_clock)) ||
qemu_timer_expired(active_timers[QEMU_TIMER_REALTIME],
qemu_get_clock(rt_clock))) {
@@ -1243,6 +1288,97 @@

#endif /* !defined(__linux__) */

+#ifdef DYNAMIC_TICKS
+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;
+#if defined(TARGET_I386) && defined(USE_CODE_COPY)
+ act.sa_flags |= SA_ONSTACK;
+#endif
+ act.sa_handler = host_alarm_handler;
+
+ sigaction(SIGALRM, &act, NULL);
+
+ 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 *)host_timer;
+
+ return 0;
+}
+
+static void dynticks_stop_timer(struct qemu_alarm_timer *t)
+{
+ timer_t host_timer = (timer_t)t->priv;
+
+ timer_delete(host_timer);
+}
+
+static void dynticks_rearm_timer(struct qemu_alarm_timer *t)
+{
+ timer_t host_timer = (timer_t)t->priv;
+ struct itimerspec timeout;
+ int64_t nearest_delta_us = INT64_MAX;
+
+ if (active_timers[QEMU_TIMER_REALTIME] ||
+ active_timers[QEMU_TIMER_VIRTUAL]) {
+ int64_t vmdelta_us, current_us;
+
+ if (active_timers[QEMU_TIMER_REALTIME])
+ nearest_delta_us = (active_timers[QEMU_TIMER_REALTIME]->expire_time - qemu_get_clock(rt_clock))*1000;
+
+ if (active_timers[QEMU_TIMER_VIRTUAL]) {
+ /* round up */
+ vmdelta_us = (active_timers[QEMU_TIMER_VIRTUAL]->expire_time - qemu_get_clock(vm_clock)+999)/1000;
+ if (vmdelta_us < nearest_delta_us)
+ nearest_delta_us = vmdelta_us;
+ }
+
+ /* Avoid arming the timer to negative, zero, or too low values */
+ /* TODO: MIN_TIMER_REARM_US should be optimized */
+ #define MIN_TIMER_REARM_US 250
+ if (nearest_delta_us <= MIN_TIMER_REARM_US)
+ nearest_delta_us = MIN_TIMER_REARM_US;
+
+ /* 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 /* DYNAMIC_TICKS */
+
static int unix_start_timer(struct qemu_alarm_timer *t)
{
struct sigaction act;
@@ -6490,6 +6626,7 @@
cpu_enable_ticks();
vm_running = 1;
vm_state_notify(1);
+ qemu_rearm_alarm_timer(alarm_timer);
}
}

Index: qemu/configure
===================================================================
--- qemu.orig/configure 2007-08-17 17:45:17.000000000 +0200
+++ qemu/configure 2007-08-17 17:45:31.000000000 +0200
@@ -294,6 +294,8 @@
*) echo "undefined SPARC architecture. Exiting";exit 1;;
esac
;;
+ --disable-dynamic-ticks) dynamic_ticks="no"
+ ;;
esac
done

@@ -859,6 +861,9 @@
if [ "$build_docs" = "yes" ] ; then
echo "BUILD_DOCS=yes" >> $config_mak
fi
+if test "$dynamic_ticks" != "no" ; then
+ echo "#define DYNAMIC_TICKS 1" >> $config_h
+fi

# XXX: suppress that
if [ "$bsd" = "yes" ] ; then

--