event: add timer accuracy/coalescing logic

In order to improve energy consumption we should minimize our wake-ups
when handling timers.  Hence, for each timer take an accuracy value and
schedule the actual wake-up time somewhere between the specified time
and the specified timer plus the accuracy.

The specified time of timer event sources hence becomes the time the
handler is called the *earliest*, and the specified time plus the accuracy
the time by which it is called the *latest*, leaving the library the
freedom to schedule the wake-up somewhere inbetween.

If the accuracy is specified as 0 the default of 250ms will be used.

When scheduling timeouts we will now try to elapse them at the same
point within each second, across the entire system. We do this by using
a fixed perturbation value keyed off the boot id. If this point within a
second is not in the acceptable range, we try again with a fixed time
within each 250ms time step. If that doesn't work either, we wake up at
the last possible time.

4 files changed, 275 insertions, 76 deletions

diff --git a/src/libsystemd-bus/sd-event.c b/src/libsystemd-bus/sd-event.c
index de96fde8e2..511b271d45 100644
--- a/src/libsystemd-bus/sd-event.c
+++ b/src/libsystemd-bus/sd-event.c
@@ -29,10 +29,12 @@
 #include "hashmap.h"
 #include "util.h"
 #include "time-util.h"
+#include "sd-id128.h"
 
 #include "sd-event.h"
 
 #define EPOLL_QUEUE_MAX 64
+#define DEFAULT_ACCURACY_USEC (250 * USEC_PER_MSEC)
 
 typedef enum EventSourceType {
         SOURCE_IO,
@@ -70,8 +72,9 @@ struct sd_event_source {
                 } io;
                 struct {
                         sd_time_handler_t callback;
-                        usec_t next;
-                        unsigned prioq_index;
+                        usec_t next, accuracy;
+                        unsigned earliest_index;
+                        unsigned latest_index;
                 } time;
                 struct {
                         sd_signal_handler_t callback;
@@ -100,8 +103,17 @@ struct sd_event {
 
         Prioq *pending;
         Prioq *prepare;
-        Prioq *monotonic;
-        Prioq *realtime;
+
+        /* For both clocks we maintain two priority queues each, one
+         * ordered for the earliest times the events may be
+         * dispatched, and one ordered by the latest times they must
+         * have been dispatched. The range between the top entries in
+         * the two prioqs is the time window we can freely schedule
+         * wakeups in */
+        Prioq *monotonic_earliest;
+        Prioq *monotonic_latest;
+        Prioq *realtime_earliest;
+        Prioq *realtime_latest;
 
         sigset_t sigset;
         sd_event_source **signal_sources;
@@ -110,11 +122,13 @@ struct sd_event {
         unsigned n_unmuted_child_sources;
 
         unsigned iteration;
-        unsigned processed_children;
 
         usec_t realtime_next, monotonic_next;
 
+        usec_t perturb;
+
         bool quit;
+        bool need_process_child;
 };
 
 static int pending_prioq_compare(const void *a, const void *b) {
@@ -185,7 +199,7 @@ static int prepare_prioq_compare(const void *a, const void *b) {
         return 0;
 }
 
-static int time_prioq_compare(const void *a, const void *b) {
+static int earliest_time_prioq_compare(const void *a, const void *b) {
         const sd_event_source *x = a, *y = b;
 
         assert(x->type == SOURCE_MONOTONIC || x->type == SOURCE_REALTIME);
@@ -218,6 +232,39 @@ static int time_prioq_compare(const void *a, const void *b) {
         return 0;
 }
 
+static int latest_time_prioq_compare(const void *a, const void *b) {
+        const sd_event_source *x = a, *y = b;
+
+        assert(x->type == SOURCE_MONOTONIC || x->type == SOURCE_REALTIME);
+        assert(y->type == SOURCE_MONOTONIC || y->type == SOURCE_REALTIME);
+
+        /* Unmuted ones first */
+        if (x->mute != SD_EVENT_MUTED && y->mute == SD_EVENT_MUTED)
+                return -1;
+        if (x->mute == SD_EVENT_MUTED && y->mute != SD_EVENT_MUTED)
+                return 1;
+
+        /* Move the pending ones to the end */
+        if (!x->pending && y->pending)
+                return -1;
+        if (x->pending && !y->pending)
+                return 1;
+
+        /* Order by time */
+        if (x->time.next + x->time.accuracy < y->time.next + y->time.accuracy)
+                return -1;
+        if (x->time.next + x->time.accuracy > y->time.next + y->time.accuracy)
+                return -1;
+
+        /* Stability for the rest */
+        if (x < y)
+                return -1;
+        if (x > y)
+                return 1;
+
+        return 0;
+}
+
 static void event_free(sd_event *e) {
         assert(e);
 
@@ -235,8 +282,10 @@ static void event_free(sd_event *e) {
 
         prioq_free(e->pending);
         prioq_free(e->prepare);
-        prioq_free(e->monotonic);
-        prioq_free(e->realtime);
+        prioq_free(e->monotonic_earliest);
+        prioq_free(e->monotonic_latest);
+        prioq_free(e->realtime_earliest);
+        prioq_free(e->realtime_latest);
 
         free(e->signal_sources);
 
@@ -357,11 +406,13 @@ static void source_free(sd_event_source *s) {
                         break;
 
                 case SOURCE_MONOTONIC:
-                        prioq_remove(s->event->monotonic, s, &s->time.prioq_index);
+                        prioq_remove(s->event->monotonic_earliest, s, &s->time.earliest_index);
+                        prioq_remove(s->event->monotonic_latest, s, &s->time.latest_index);
                         break;
 
                 case SOURCE_REALTIME:
-                        prioq_remove(s->event->realtime, s, &s->time.prioq_index);
+                        prioq_remove(s->event->realtime_earliest, s, &s->time.earliest_index);
+                        prioq_remove(s->event->realtime_latest, s, &s->time.latest_index);
                         break;
 
                 case SOURCE_SIGNAL:
@@ -494,6 +545,7 @@ static int event_setup_timer_fd(
 
         struct epoll_event ev = {};
         int r, fd;
+        sd_id128_t bootid;
 
         assert(e);
         assert(timer_fd);
@@ -514,6 +566,17 @@ static int event_setup_timer_fd(
                 return -errno;
         }
 
+        /* When we sleep for longer, we try to realign the wakeup to
+           the same time wihtin each second, so that events all across
+           the system can be coalesced into a single CPU
+           wakeup. However, let's take some system-specific randomness
+           for this value, so that in a network of systems with synced
+           clocks timer events are distributed a bit. Here, we
+           calculate a perturbation usec offset from the boot ID. */
+
+        if (sd_id128_get_boot(&bootid) >= 0)
+                e->perturb = (bootid.qwords[0] ^ bootid.qwords[1]) % USEC_PER_SEC;
+
         *timer_fd = fd;
         return 0;
 }
@@ -523,8 +586,10 @@ static int event_add_time_internal(
                 EventSourceType type,
                 int *timer_fd,
                 clockid_t id,
-                Prioq **prioq,
+                Prioq **earliest,
+                Prioq **latest,
                 uint64_t usec,
+                uint64_t accuracy,
                 sd_time_handler_t callback,
                 void *userdata,
                 sd_event_source **ret) {
@@ -538,13 +603,24 @@ static int event_add_time_internal(
                 return -EINVAL;
         if (!ret)
                 return -EINVAL;
+        if (usec == (uint64_t) -1)
+                return -EINVAL;
+        if (accuracy == (uint64_t) -1)
+                return -EINVAL;
 
         assert(timer_fd);
-        assert(prioq);
+        assert(earliest);
+        assert(latest);
+
+        if (!*earliest) {
+                *earliest = prioq_new(earliest_time_prioq_compare);
+                if (!*earliest)
+                        return -ENOMEM;
+        }
 
-        if (!*prioq) {
-                *prioq = prioq_new(time_prioq_compare);
-                if (!*prioq)
+        if (!*latest) {
+                *latest = prioq_new(latest_time_prioq_compare);
+                if (!*latest)
                         return -ENOMEM;
         }
 
@@ -559,26 +635,34 @@ static int event_add_time_internal(
                 return -ENOMEM;
 
         s->time.next = usec;
+        s->time.accuracy = accuracy == 0 ? DEFAULT_ACCURACY_USEC : accuracy;
         s->time.callback = callback;
-        s->time.prioq_index = PRIOQ_IDX_NULL;
+        s->time.earliest_index = PRIOQ_IDX_NULL;
+        s->time.latest_index = PRIOQ_IDX_NULL;
         s->userdata = userdata;
 
-        r = prioq_put(*prioq, s, &s->time.prioq_index);
-        if (r < 0) {
-                source_free(s);
-                return r;
-        }
+        r = prioq_put(*earliest, s, &s->time.earliest_index);
+        if (r < 0)
+                goto fail;
+
+        r = prioq_put(*latest, s, &s->time.latest_index);
+        if (r < 0)
+                goto fail;
 
         *ret = s;
         return 0;
+
+fail:
+        source_free(s);
+        return r;
 }
 
-int sd_event_add_monotonic(sd_event *e, uint64_t usec, sd_time_handler_t callback, void *userdata, sd_event_source **ret) {
-        return event_add_time_internal(e, SOURCE_MONOTONIC, &e->monotonic_fd, CLOCK_MONOTONIC, &e->monotonic, usec, callback, userdata, ret);
+int sd_event_add_monotonic(sd_event *e, uint64_t usec, uint64_t accuracy, sd_time_handler_t callback, void *userdata, sd_event_source **ret) {
+        return event_add_time_internal(e, SOURCE_MONOTONIC, &e->monotonic_fd, CLOCK_MONOTONIC, &e->monotonic_earliest, &e->monotonic_latest, usec, accuracy, callback, userdata, ret);
 }
 
-int sd_event_add_realtime(sd_event *e, uint64_t usec, sd_time_handler_t callback, void *userdata, sd_event_source **ret) {
-        return event_add_time_internal(e, SOURCE_REALTIME, &e->realtime_fd, CLOCK_REALTIME, &e->realtime, usec, callback, userdata, ret);
+int sd_event_add_realtime(sd_event *e, uint64_t usec, uint64_t accuracy, sd_time_handler_t callback, void *userdata, sd_event_source **ret) {
+        return event_add_time_internal(e, SOURCE_REALTIME, &e->realtime_fd, CLOCK_REALTIME, &e->realtime_earliest, &e->monotonic_latest, usec, accuracy, callback, userdata, ret);
 }
 
 static int event_update_signal_fd(sd_event *e) {
@@ -707,6 +791,8 @@ int sd_event_add_child(sd_event *e, pid_t pid, int options, sd_child_handler_t c
                 }
         }
 
+        e->need_process_child = true;
+
         *ret = s;
         return 0;
 }
@@ -848,10 +934,10 @@ int sd_event_source_set_priority(sd_event_source *s, int priority) {
         s->priority = priority;
 
         if (s->pending)
-                assert_se(prioq_reshuffle(s->event->pending, s, &s->pending_index) == 0);
+                prioq_reshuffle(s->event->pending, s, &s->pending_index);
 
         if (s->prepare)
-                assert_se(prioq_reshuffle(s->event->prepare, s, &s->prepare_index) == 0);
+                prioq_reshuffle(s->event->prepare, s, &s->prepare_index);
 
         return 0;
 }
@@ -891,12 +977,14 @@ int sd_event_source_set_mute(sd_event_source *s, sd_event_mute_t m) {
 
                 case SOURCE_MONOTONIC:
                         s->mute = m;
-                        prioq_reshuffle(s->event->monotonic, s, &s->time.prioq_index);
+                        prioq_reshuffle(s->event->monotonic_earliest, s, &s->time.earliest_index);
+                        prioq_reshuffle(s->event->monotonic_latest, s, &s->time.latest_index);
                         break;
 
                 case SOURCE_REALTIME:
                         s->mute = m;
-                        prioq_reshuffle(s->event->realtime, s, &s->time.prioq_index);
+                        prioq_reshuffle(s->event->realtime_earliest, s, &s->time.earliest_index);
+                        prioq_reshuffle(s->event->realtime_latest, s, &s->time.latest_index);
                         break;
 
                 case SOURCE_SIGNAL:
@@ -939,12 +1027,14 @@ int sd_event_source_set_mute(sd_event_source *s, sd_event_mute_t m) {
 
                 case SOURCE_MONOTONIC:
                         s->mute = m;
-                        prioq_reshuffle(s->event->monotonic, s, &s->time.prioq_index);
+                        prioq_reshuffle(s->event->monotonic_earliest, s, &s->time.earliest_index);
+                        prioq_reshuffle(s->event->monotonic_latest, s, &s->time.latest_index);
                         break;
 
                 case SOURCE_REALTIME:
                         s->mute = m;
-                        prioq_reshuffle(s->event->realtime, s, &s->time.prioq_index);
+                        prioq_reshuffle(s->event->realtime_earliest, s, &s->time.earliest_index);
+                        prioq_reshuffle(s->event->realtime_latest, s, &s->time.latest_index);
                         break;
 
                 case SOURCE_SIGNAL:
@@ -999,6 +1089,8 @@ int sd_event_source_get_time(sd_event_source *s, uint64_t *usec) {
 int sd_event_source_set_time(sd_event_source *s, uint64_t usec) {
         if (!s)
                 return -EINVAL;
+        if (usec == (uint64_t) -1)
+                return -EINVAL;
         if (s->type != SOURCE_REALTIME && s->type != SOURCE_MONOTONIC)
                 return -EDOM;
 
@@ -1007,10 +1099,13 @@ int sd_event_source_set_time(sd_event_source *s, uint64_t usec) {
 
         s->time.next = usec;
 
-        if (s->type == SOURCE_REALTIME)
-                prioq_reshuffle(s->event->realtime, s, &s->time.prioq_index);
-        else
-                prioq_reshuffle(s->event->monotonic, s, &s->time.prioq_index);
+        if (s->type == SOURCE_REALTIME) {
+                prioq_reshuffle(s->event->realtime_earliest, s, &s->time.earliest_index);
+                prioq_reshuffle(s->event->realtime_latest, s, &s->time.latest_index);
+        } else {
+                prioq_reshuffle(s->event->monotonic_earliest, s, &s->time.earliest_index);
+                prioq_reshuffle(s->event->monotonic_latest, s, &s->time.latest_index);
+        }
 
         return 0;
 }
@@ -1052,40 +1147,99 @@ void* sd_event_source_get_userdata(sd_event_source *s) {
         return s->userdata;
 }
 
+static usec_t sleep_between(sd_event *e, usec_t a, usec_t b) {
+        usec_t c;
+        assert(e);
+        assert(a <= b);
+
+        if (a <= 0)
+                return 0;
+
+        if (b <= a + 1)
+                return a;
+
+        /*
+          Find a good time to wake up again between times a and b. We
+          have two goals here:
+
+          a) We want to wake up as seldom as possible, hence prefer
+             later times over earlier times.
+
+          b) But if we have to wake up, then let's make sure to
+             dispatch as much as possible on the entire system.
+
+          We implement this by waking up everywhere at the same time
+          within any given second if we can, synchronised via the
+          perturbation value determined from the boot ID. If we can't,
+          then we try to find the same spot in every a 250ms
+          step. Otherwise, we pick the last possible time to wake up.
+        */
+
+        c = (b / USEC_PER_SEC) * USEC_PER_SEC + e->perturb;
+        if (c >= b) {
+                if (_unlikely_(c < USEC_PER_SEC))
+                        return b;
+
+                c -= USEC_PER_SEC;
+        }
+
+        if (c >= a)
+                return c;
+
+        c = (b / (USEC_PER_MSEC*250)) * (USEC_PER_MSEC*250) + (e->perturb % (USEC_PER_MSEC*250));
+        if (c >= b) {
+                if (_unlikely_(c < USEC_PER_MSEC*250))
+                        return b;
+
+                c -= USEC_PER_MSEC*250;
+        }
+
+        if (c >= a)
+                return c;
+
+        return b;
+}
+
 static int event_arm_timer(
                 sd_event *e,
                 int timer_fd,
-                Prioq *prioq,
+                Prioq *earliest,
+                Prioq *latest,
                 usec_t *next) {
 
         struct itimerspec its = {};
-        sd_event_source *s;
+        sd_event_source *a, *b;
+        usec_t t;
         int r;
 
         assert_se(e);
         assert_se(next);
 
-        s = prioq_peek(prioq);
-        if (!s || s->mute == SD_EVENT_MUTED)
+        a = prioq_peek(earliest);
+        if (!a || a->mute == SD_EVENT_MUTED)
                 return 0;
 
-        if (*next == s->time.next)
+        b = prioq_peek(latest);
+        assert_se(b && b->mute != SD_EVENT_MUTED);
+
+        t = sleep_between(e, a->time.next, b->time.next + b->time.accuracy);
+        if (*next == t)
                 return 0;
 
         assert_se(timer_fd >= 0);
 
-        if (s->time.next == 0) {
+        if (t == 0) {
                 /* We don' want to disarm here, just mean some time looooong ago. */
                 its.it_value.tv_sec = 0;
                 its.it_value.tv_nsec = 1;
         } else
-                timespec_store(&its.it_value, s->time.next);
+                timespec_store(&its.it_value, t);
 
         r = timerfd_settime(timer_fd, TFD_TIMER_ABSTIME, &its, NULL);
         if (r < 0)
                 return r;
 
-        *next = s->time.next;
+        *next = t;
         return 0;
 }
 
@@ -1131,14 +1285,14 @@ static int flush_timer(sd_event *e, int fd, uint32_t events) {
         return 0;
 }
 
-static int process_timer(sd_event *e, usec_t n, Prioq *prioq) {
+static int process_timer(sd_event *e, usec_t n, Prioq *earliest, Prioq *latest) {
         sd_event_source *s;
         int r;
 
         assert(e);
 
         for (;;) {
-                s = prioq_peek(prioq);
+                s = prioq_peek(earliest);
                 if (!s ||
                     s->time.next > n ||
                     s->mute == SD_EVENT_MUTED ||
@@ -1149,9 +1303,8 @@ static int process_timer(sd_event *e, usec_t n, Prioq *prioq) {
                 if (r < 0)
                         return r;
 
-                r = prioq_reshuffle(prioq, s, &s->time.prioq_index);
-                if (r < 0)
-                        return r;
+                prioq_reshuffle(earliest, s, &s->time.earliest_index);
+                prioq_reshuffle(latest, s, &s->time.latest_index);
         }
 
         return 0;
@@ -1164,6 +1317,8 @@ static int process_child(sd_event *e) {
 
         assert(e);
 
+        e->need_process_child = false;
+
         /*
            So, this is ugly. We iteratively invoke waitid() with P_PID
            + WNOHANG for each PID we wait for, instead of using
@@ -1199,7 +1354,6 @@ static int process_child(sd_event *e) {
                 }
         }
 
-        e->processed_children = e->iteration;
         return 0;
 }
 
@@ -1323,6 +1477,19 @@ static int event_prepare(sd_event *e) {
         return 0;
 }
 
+static sd_event_source* event_next_pending(sd_event *e) {
+        sd_event_source *p;
+
+        p = prioq_peek(e->pending);
+        if (!p)
+                return NULL;
+
+        if (p->mute == SD_EVENT_MUTED)
+                return NULL;
+
+        return p;
+}
+
 int sd_event_run(sd_event *e, uint64_t timeout) {
         struct epoll_event ev_queue[EPOLL_QUEUE_MAX];
         sd_event_source *p;
@@ -1340,25 +1507,21 @@ int sd_event_run(sd_event *e, uint64_t timeout) {
         if (r < 0)
                 return r;
 
-        r = event_arm_timer(e, e->monotonic_fd, e->monotonic, &e->monotonic_next);
-        if (r < 0)
-                return r;
+        if (event_next_pending(e) || e->need_process_child)
+                timeout = 0;
 
-        r = event_arm_timer(e, e->realtime_fd, e->realtime, &e->realtime_next);
-        if (r < 0)
-                return r;
+        if (timeout > 0) {
+                r = event_arm_timer(e, e->monotonic_fd, e->monotonic_earliest, e->monotonic_latest, &e->monotonic_next);
+                if (r < 0)
+                        return r;
 
-        if (e->iteration == 1 && !hashmap_isempty(e->child_sources))
-                /* On the first iteration, there might be already some
-                 * zombies for us to care for, hence, don't wait */
-                timeout = 0;
-        else {
-                p = prioq_peek(e->pending);
-                if (p && p->mute != SD_EVENT_MUTED)
-                        timeout = 0;
+                r = event_arm_timer(e, e->realtime_fd, e->realtime_earliest, e->realtime_latest, &e->realtime_next);
+                if (r < 0)
+                        return r;
         }
 
-        m = epoll_wait(e->epoll_fd, ev_queue, EPOLL_QUEUE_MAX, timeout == (uint64_t) -1 ? -1 : (int) ((timeout + USEC_PER_MSEC - 1) / USEC_PER_MSEC));
+        m = epoll_wait(e->epoll_fd, ev_queue, EPOLL_QUEUE_MAX,
+                       timeout == (uint64_t) -1 ? -1 : (int) ((timeout + USEC_PER_MSEC - 1) / USEC_PER_MSEC));
         if (m < 0)
                 return m;
 
@@ -1379,24 +1542,22 @@ int sd_event_run(sd_event *e, uint64_t timeout) {
                         return r;
         }
 
-        r = process_timer(e, n.monotonic, e->monotonic);
+        r = process_timer(e, n.monotonic, e->monotonic_earliest, e->monotonic_latest);
         if (r < 0)
                 return r;
 
-        r = process_timer(e, n.realtime, e->realtime);
+        r = process_timer(e, n.realtime, e->realtime_earliest, e->realtime_latest);
         if (r < 0)
                 return r;
 
-        if (e->iteration == 1 && e->processed_children != 1) {
-                /* On the first iteration, make sure we really process
-                 * all children which might already be zombies. */
+        if (e->need_process_child) {
                 r = process_child(e);
                 if (r < 0)
                         return r;
         }
 
-        p = prioq_peek(e->pending);
-        if (!p || p->mute == SD_EVENT_MUTED)
+        p = event_next_pending(e);
+        if (!p)
                 return 0;
 
         return source_dispatch(p);
@@ -1438,3 +1599,38 @@ sd_event *sd_event_get(sd_event_source *s) {
 
         return s->event;
 }
+
+int sd_event_source_set_time_accuracy(sd_event_source *s, uint64_t usec) {
+        if (!s)
+                return -EINVAL;
+        if (s->type != SOURCE_MONOTONIC && s->type != SOURCE_REALTIME)
+                return -EDOM;
+
+        if (usec == 0)
+                usec = DEFAULT_ACCURACY_USEC;
+
+        if (s->time.accuracy == usec)
+                return 0;
+
+
+        s->time.accuracy = usec;
+
+        if (s->type == SOURCE_REALTIME)
+                prioq_reshuffle(s->event->realtime_latest, s, &s->time.latest_index);
+        else
+                prioq_reshuffle(s->event->monotonic_latest, s, &s->time.latest_index);
+
+        return 0;
+}
+
+int sd_event_source_get_time_accuracy(sd_event_source *s, uint64_t *usec) {
+        if (!s)
+                return -EINVAL;
+        if (!usec)
+                return -EINVAL;
+        if (s->type != SOURCE_MONOTONIC && s->type != SOURCE_REALTIME)
+                return -EDOM;
+
+        *usec = s->time.accuracy;
+        return 0;
+}
diff --git a/src/libsystemd-bus/test-event.c b/src/libsystemd-bus/test-event.c
index 8dd47fe8a9..acb5cee367 100644
--- a/src/libsystemd-bus/test-event.c
+++ b/src/libsystemd-bus/test-event.c
@@ -151,7 +151,7 @@ int main(int argc, char *argv[]) {
 
         assert_se(sd_event_add_io(e, a[0], EPOLLIN, io_handler, INT_TO_PTR('a'), &x) >= 0);
         assert_se(sd_event_add_io(e, b[0], EPOLLIN, io_handler, INT_TO_PTR('b'), &y) >= 0);
-        assert_se(sd_event_add_monotonic(e, 0, time_handler, INT_TO_PTR('c'), &z) >= 0);
+        assert_se(sd_event_add_monotonic(e, 0, 0, time_handler, INT_TO_PTR('c'), &z) >= 0);
 
         assert_se(sd_event_source_set_priority(x, 99) >= 0);
         assert_se(sd_event_source_set_mute(y, SD_EVENT_ONESHOT) >= 0);
diff --git a/src/shared/prioq.c b/src/shared/prioq.c
index 2d166360aa..537befc623 100644
--- a/src/shared/prioq.c
+++ b/src/shared/prioq.c
@@ -217,7 +217,8 @@ _pure_ static struct prioq_item* find_item(Prioq *q, void *data, unsigned *idx)
         assert(q);
 
         if (idx) {
-                if (*idx > q->n_items)
+                if (*idx == PRIOQ_IDX_NULL ||
+                    *idx > q->n_items)
                         return NULL;
 
                 i = q->items + *idx;
diff --git a/src/systemd/sd-event.h b/src/systemd/sd-event.h
index bec41cff6d..90fea4e17a 100644
--- a/src/systemd/sd-event.h
+++ b/src/systemd/sd-event.h
@@ -38,7 +38,7 @@
   TODO:
 
   - Detect forks and return ECHILD
-  - Timer events with accuracy for coalescing time events
+  - quit hooks
 */
 
 typedef struct sd_event sd_event;
@@ -62,8 +62,8 @@ sd_event* sd_event_ref(sd_event *e);
 sd_event* sd_event_unref(sd_event *e);
 
 int sd_event_add_io(sd_event *e, int fd, uint32_t events, sd_io_handler_t callback, void *userdata, sd_event_source **s);
-int sd_event_add_monotonic(sd_event *e, uint64_t usec, sd_time_handler_t callback, void *userdata, sd_event_source **s);
-int sd_event_add_realtime(sd_event *e, uint64_t usec, sd_time_handler_t callback, void *userdata, sd_event_source **s);
+int sd_event_add_monotonic(sd_event *e, uint64_t usec, uint64_t accuracy, sd_time_handler_t callback, void *userdata, sd_event_source **s);
+int sd_event_add_realtime(sd_event *e, uint64_t usec, uint64_t accuracy, sd_time_handler_t callback, void *userdata, sd_event_source **s);
 int sd_event_add_signal(sd_event *e, int sig, sd_signal_handler_t callback, void *userdata, sd_event_source **s);
 int sd_event_add_child(sd_event *e, pid_t pid, int options, sd_child_handler_t callback, void *userdata, sd_event_source **s);
 int sd_event_add_defer(sd_event *e, sd_defer_handler_t callback, void *userdata, sd_event_source **s);
@@ -91,6 +91,8 @@ int sd_event_source_get_mute(sd_event_source *s, sd_event_mute_t *m);
 int sd_event_source_set_mute(sd_event_source *s, sd_event_mute_t m);
 int sd_event_source_get_time(sd_event_source *s, uint64_t *usec);
 int sd_event_source_set_time(sd_event_source *s, uint64_t usec);
+int sd_event_source_set_time_accuracy(sd_event_source *s, uint64_t usec);
+int sd_event_source_get_time_accuracy(sd_event_source *s, uint64_t *usec);
 int sd_event_source_set_prepare(sd_event_source *s, sd_prepare_handler_t callback);
 void* sd_event_source_get_userdata(sd_event_source *s);