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monitor: Simplify event throttling

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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>
This commit is contained in:
Markus Armbruster 2015-10-15 17:08:31 +02:00
parent 688b4b7de7
commit 93f8f982fe
2 changed files with 32 additions and 35 deletions
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63
monitor.c
View File

@ -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 = &(monitor_qapi_event_state[event]);
trace_monitor_protocol_event_queue(event,
qdict,
evstate->rate,
evstate->last,
now);
/* 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,

4
trace-events
View File

@ -1031,9 +1031,9 @@ esp_pci_sbac_write(uint32_t reg, uint32_t val) "sbac: 0x%8.8x -> 0x%8.8x"
# monitor.c
handle_qmp_command(void *mon, const char *cmd_name) "mon %p cmd_name \"%s\""
monitor_protocol_emitter(void *mon) "mon %p"
monitor_protocol_event_handler(uint32_t event, void *data, uint64_t last, uint64_t now) "event=%d data=%p last=%" PRId64 " now=%" PRId64
monitor_protocol_event_handler(uint32_t event, void *qdict) "event=%d data=%p"
monitor_protocol_event_emit(uint32_t event, void *data) "event=%d data=%p"
monitor_protocol_event_queue(uint32_t event, void *data, uint64_t rate, uint64_t last, uint64_t now) "event=%d data=%p rate=%" PRId64 " last=%" PRId64 " now=%" PRId64
monitor_protocol_event_queue(uint32_t event, void *qdict, uint64_t rate) "event=%d data=%p rate=%" PRId64
monitor_protocol_event_throttle(uint32_t event, uint64_t rate) "event=%d rate=%" PRId64
# hw/net/opencores_eth.c