diff options
author | Markus Armbruster <armbru@redhat.com> | 2015-10-15 17:08:31 +0200 |
---|---|---|
committer | Markus Armbruster <armbru@redhat.com> | 2015-10-29 14:34:45 +0100 |
commit | 93f8f982fedfc9ee9cf5fc8983c3b25efe828967 (patch) | |
tree | 624933100cf01b286b8b52882d4a77e345afef69 /monitor.c | |
parent | 688b4b7de755f4dd01ec516975ae01590cf9f438 (diff) |
monitor: Simplify event throttling
The event throttling state machine is hard to understand. I'm not
sure it's entirely correct. Rewrite it in a more straightforward
manner:
State 1: No event sent recently (less than evconf->rate ns ago)
Invariant: evstate->timer is not pending, evstate->qdict is null
On event: send event, arm timer, goto state 2
State 2: Event sent recently, no additional event being delayed
Invariant: evstate->timer is pending, evstate->qdict is null
On event: store it in evstate->qdict, goto state 3
On timer: goto state 1
State 3: Event sent recently, additional event being delayed
Invariant: evstate->timer is pending, evstate->qdict is non-null
On event: store it in evstate->qdict, goto state 3
On timer: send evstate->qdict, clear evstate->qdict,
arm timer, goto state 2
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <1444921716-9511-3-git-send-email-armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Diffstat (limited to 'monitor.c')
-rw-r--r-- | monitor.c | 63 |
1 files changed, 30 insertions, 33 deletions
@@ -183,7 +183,6 @@ typedef struct { typedef struct MonitorQAPIEventState { QAPIEvent event; /* Event being tracked */ int64_t rate; /* Minimum time (in ns) between two events */ - int64_t last; /* QEMU_CLOCK_REALTIME value at last emission */ QEMUTimer *timer; /* Timer for handling delayed events */ QDict *qdict; /* Delayed event (if any) */ } MonitorQAPIEventState; @@ -464,65 +463,64 @@ static void monitor_qapi_event_queue(QAPIEvent event, QDict *qdict, Error **errp) { MonitorQAPIEventState *evstate; - assert(event < QAPI_EVENT_MAX); - int64_t now = qemu_clock_get_ns(QEMU_CLOCK_REALTIME); - evstate = &(monitor_qapi_event_state[event]); - trace_monitor_protocol_event_queue(event, - qdict, - evstate->rate, - evstate->last, - now); + assert(event < QAPI_EVENT_MAX); + evstate = &monitor_qapi_event_state[event]; + trace_monitor_protocol_event_queue(event, qdict, evstate->rate); - /* Rate limit of 0 indicates no throttling */ qemu_mutex_lock(&monitor_lock); + if (!evstate->rate) { + /* Unthrottled event */ monitor_qapi_event_emit(event, qdict); - evstate->last = now; } else { - int64_t delta = now - evstate->last; - if (evstate->qdict || - delta < evstate->rate) { - /* If there's an existing event pending, replace - * it with the new event, otherwise schedule a - * timer for delayed emission + if (timer_pending(evstate->timer)) { + /* + * Timer is pending for (at least) evstate->rate ns after + * last send. Store event for sending when timer fires, + * replacing a prior stored event if any. */ - if (evstate->qdict) { - QDECREF(evstate->qdict); - } else { - int64_t then = evstate->last + evstate->rate; - timer_mod_ns(evstate->timer, then); - } + QDECREF(evstate->qdict); evstate->qdict = qdict; QINCREF(evstate->qdict); } else { + /* + * Last send was (at least) evstate->rate ns ago. + * Send immediately, and arm the timer to call + * monitor_qapi_event_handler() in evstate->rate ns. Any + * events arriving before then will be delayed until then. + */ + int64_t now = qemu_clock_get_ns(QEMU_CLOCK_REALTIME); + monitor_qapi_event_emit(event, qdict); - evstate->last = now; + timer_mod_ns(evstate->timer, now + evstate->rate); } } + qemu_mutex_unlock(&monitor_lock); } /* - * The callback invoked by QemuTimer when a delayed - * event is ready to be emitted + * This function runs evstate->rate ns after sending a throttled + * event. + * If another event has since been stored, send it. */ static void monitor_qapi_event_handler(void *opaque) { MonitorQAPIEventState *evstate = opaque; - int64_t now = qemu_clock_get_ns(QEMU_CLOCK_REALTIME); - trace_monitor_protocol_event_handler(evstate->event, - evstate->qdict, - evstate->last, - now); + trace_monitor_protocol_event_handler(evstate->event, evstate->qdict); qemu_mutex_lock(&monitor_lock); + if (evstate->qdict) { + int64_t now = qemu_clock_get_ns(QEMU_CLOCK_REALTIME); + monitor_qapi_event_emit(evstate->event, evstate->qdict); QDECREF(evstate->qdict); evstate->qdict = NULL; + timer_mod_ns(evstate->timer, now + evstate->rate); } - evstate->last = now; + qemu_mutex_unlock(&monitor_lock); } @@ -546,7 +544,6 @@ monitor_qapi_event_throttle(QAPIEvent event, int64_t rate) evstate->event = event; assert(rate * SCALE_MS <= INT64_MAX); evstate->rate = rate * SCALE_MS; - evstate->last = 0; evstate->qdict = NULL; evstate->timer = timer_new(QEMU_CLOCK_REALTIME, SCALE_MS, |