qemu/util/qemu-timer.c
Paolo Bonzini 6b8f0187a4 icount: process QEMU_CLOCK_VIRTUAL timers in vCPU thread
icount has become much slower after tcg_cpu_exec has stopped
using the BQL.  There is also a latent bug that is masked by
the slowness.

The slowness happens because every occurrence of a QEMU_CLOCK_VIRTUAL
timer now has to wake up the I/O thread and wait for it.  The rendez-vous
is mediated by the BQL QemuMutex:

- handle_icount_deadline wakes up the I/O thread with BQL taken
- the I/O thread wakes up and waits on the BQL
- the VCPU thread releases the BQL a little later
- the I/O thread raises an interrupt, which calls qemu_cpu_kick
- the VCPU thread notices the interrupt, takes the BQL to
  process it and waits on it

All this back and forth is extremely expensive, causing a 6 to 8-fold
slowdown when icount is turned on.

One may think that the issue is that the VCPU thread is too dependent
on the BQL, but then the latent bug comes in.  I first tried removing
the BQL completely from the x86 cpu_exec, only to see everything break.
The only way to fix it (and make everything slow again) was to add a dummy
BQL lock/unlock pair.

This is because in -icount mode you really have to process the events
before the CPU restarts executing the next instruction.  Therefore, this
series moves the processing of QEMU_CLOCK_VIRTUAL timers straight in
the vCPU thread when running in icount mode.

The required changes include:

- make the timer notification callback wake up TCG's single vCPU thread
  when run from another thread.  By using async_run_on_cpu, the callback
  can override all_cpu_threads_idle() when the CPU is halted.

- move handle_icount_deadline after qemu_tcg_wait_io_event, so that
  the timer notification callback is invoked after the dummy work item
  wakes up the vCPU thread

- make handle_icount_deadline run the timers instead of just waking the
  I/O thread.

- stop processing the timers in the main loop

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2017-03-14 13:51:34 +01:00

668 lines
18 KiB
C

/*
* 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 "qemu/osdep.h"
#include "qemu/main-loop.h"
#include "qemu/timer.h"
#include "sysemu/replay.h"
#include "sysemu/sysemu.h"
#include "sysemu/cpus.h"
#ifdef CONFIG_POSIX
#include <pthread.h>
#endif
#ifdef CONFIG_PPOLL
#include <poll.h>
#endif
#ifdef CONFIG_PRCTL_PR_SET_TIMERSLACK
#include <sys/prctl.h>
#endif
/***********************************************************/
/* timers */
typedef struct QEMUClock {
/* We rely on BQL to protect the timerlists */
QLIST_HEAD(, QEMUTimerList) timerlists;
NotifierList reset_notifiers;
int64_t last;
QEMUClockType type;
bool enabled;
} QEMUClock;
QEMUTimerListGroup main_loop_tlg;
static QEMUClock qemu_clocks[QEMU_CLOCK_MAX];
/* A QEMUTimerList is a list of timers attached to a clock. More
* than one QEMUTimerList can be attached to each clock, for instance
* used by different AioContexts / threads. Each clock also has
* a list of the QEMUTimerLists associated with it, in order that
* reenabling the clock can call all the notifiers.
*/
struct QEMUTimerList {
QEMUClock *clock;
QemuMutex active_timers_lock;
QEMUTimer *active_timers;
QLIST_ENTRY(QEMUTimerList) list;
QEMUTimerListNotifyCB *notify_cb;
void *notify_opaque;
/* lightweight method to mark the end of timerlist's running */
QemuEvent timers_done_ev;
};
/**
* qemu_clock_ptr:
* @type: type of clock
*
* Translate a clock type into a pointer to QEMUClock object.
*
* Returns: a pointer to the QEMUClock object
*/
static inline QEMUClock *qemu_clock_ptr(QEMUClockType type)
{
return &qemu_clocks[type];
}
static bool timer_expired_ns(QEMUTimer *timer_head, int64_t current_time)
{
return timer_head && (timer_head->expire_time <= current_time);
}
QEMUTimerList *timerlist_new(QEMUClockType type,
QEMUTimerListNotifyCB *cb,
void *opaque)
{
QEMUTimerList *timer_list;
QEMUClock *clock = qemu_clock_ptr(type);
timer_list = g_malloc0(sizeof(QEMUTimerList));
qemu_event_init(&timer_list->timers_done_ev, true);
timer_list->clock = clock;
timer_list->notify_cb = cb;
timer_list->notify_opaque = opaque;
qemu_mutex_init(&timer_list->active_timers_lock);
QLIST_INSERT_HEAD(&clock->timerlists, timer_list, list);
return timer_list;
}
void timerlist_free(QEMUTimerList *timer_list)
{
assert(!timerlist_has_timers(timer_list));
if (timer_list->clock) {
QLIST_REMOVE(timer_list, list);
}
qemu_mutex_destroy(&timer_list->active_timers_lock);
g_free(timer_list);
}
static void qemu_clock_init(QEMUClockType type, QEMUTimerListNotifyCB *notify_cb)
{
QEMUClock *clock = qemu_clock_ptr(type);
/* Assert that the clock of type TYPE has not been initialized yet. */
assert(main_loop_tlg.tl[type] == NULL);
clock->type = type;
clock->enabled = (type == QEMU_CLOCK_VIRTUAL ? false : true);
clock->last = INT64_MIN;
QLIST_INIT(&clock->timerlists);
notifier_list_init(&clock->reset_notifiers);
main_loop_tlg.tl[type] = timerlist_new(type, notify_cb, NULL);
}
bool qemu_clock_use_for_deadline(QEMUClockType type)
{
return !(use_icount && (type == QEMU_CLOCK_VIRTUAL));
}
void qemu_clock_notify(QEMUClockType type)
{
QEMUTimerList *timer_list;
QEMUClock *clock = qemu_clock_ptr(type);
QLIST_FOREACH(timer_list, &clock->timerlists, list) {
timerlist_notify(timer_list);
}
}
/* Disabling the clock will wait for related timerlists to stop
* executing qemu_run_timers. Thus, this functions should not
* be used from the callback of a timer that is based on @clock.
* Doing so would cause a deadlock.
*
* Caller should hold BQL.
*/
void qemu_clock_enable(QEMUClockType type, bool enabled)
{
QEMUClock *clock = qemu_clock_ptr(type);
QEMUTimerList *tl;
bool old = clock->enabled;
clock->enabled = enabled;
if (enabled && !old) {
qemu_clock_notify(type);
} else if (!enabled && old) {
QLIST_FOREACH(tl, &clock->timerlists, list) {
qemu_event_wait(&tl->timers_done_ev);
}
}
}
bool timerlist_has_timers(QEMUTimerList *timer_list)
{
return !!atomic_read(&timer_list->active_timers);
}
bool qemu_clock_has_timers(QEMUClockType type)
{
return timerlist_has_timers(
main_loop_tlg.tl[type]);
}
bool timerlist_expired(QEMUTimerList *timer_list)
{
int64_t expire_time;
if (!atomic_read(&timer_list->active_timers)) {
return false;
}
qemu_mutex_lock(&timer_list->active_timers_lock);
if (!timer_list->active_timers) {
qemu_mutex_unlock(&timer_list->active_timers_lock);
return false;
}
expire_time = timer_list->active_timers->expire_time;
qemu_mutex_unlock(&timer_list->active_timers_lock);
return expire_time <= qemu_clock_get_ns(timer_list->clock->type);
}
bool qemu_clock_expired(QEMUClockType type)
{
return timerlist_expired(
main_loop_tlg.tl[type]);
}
/*
* As above, but return -1 for no deadline, and do not cap to 2^32
* as we know the result is always positive.
*/
int64_t timerlist_deadline_ns(QEMUTimerList *timer_list)
{
int64_t delta;
int64_t expire_time;
if (!atomic_read(&timer_list->active_timers)) {
return -1;
}
if (!timer_list->clock->enabled) {
return -1;
}
/* The active timers list may be modified before the caller uses our return
* value but ->notify_cb() is called when the deadline changes. Therefore
* the caller should notice the change and there is no race condition.
*/
qemu_mutex_lock(&timer_list->active_timers_lock);
if (!timer_list->active_timers) {
qemu_mutex_unlock(&timer_list->active_timers_lock);
return -1;
}
expire_time = timer_list->active_timers->expire_time;
qemu_mutex_unlock(&timer_list->active_timers_lock);
delta = expire_time - qemu_clock_get_ns(timer_list->clock->type);
if (delta <= 0) {
return 0;
}
return delta;
}
/* Calculate the soonest deadline across all timerlists attached
* to the clock. This is used for the icount timeout so we
* ignore whether or not the clock should be used in deadline
* calculations.
*/
int64_t qemu_clock_deadline_ns_all(QEMUClockType type)
{
int64_t deadline = -1;
QEMUTimerList *timer_list;
QEMUClock *clock = qemu_clock_ptr(type);
QLIST_FOREACH(timer_list, &clock->timerlists, list) {
deadline = qemu_soonest_timeout(deadline,
timerlist_deadline_ns(timer_list));
}
return deadline;
}
QEMUClockType timerlist_get_clock(QEMUTimerList *timer_list)
{
return timer_list->clock->type;
}
QEMUTimerList *qemu_clock_get_main_loop_timerlist(QEMUClockType type)
{
return main_loop_tlg.tl[type];
}
void timerlist_notify(QEMUTimerList *timer_list)
{
if (timer_list->notify_cb) {
timer_list->notify_cb(timer_list->notify_opaque, timer_list->clock->type);
} else {
qemu_notify_event();
}
}
/* Transition function to convert a nanosecond timeout to ms
* This is used where a system does not support ppoll
*/
int qemu_timeout_ns_to_ms(int64_t ns)
{
int64_t ms;
if (ns < 0) {
return -1;
}
if (!ns) {
return 0;
}
/* Always round up, because it's better to wait too long than to wait too
* little and effectively busy-wait
*/
ms = DIV_ROUND_UP(ns, SCALE_MS);
/* To avoid overflow problems, limit this to 2^31, i.e. approx 25 days */
if (ms > (int64_t) INT32_MAX) {
ms = INT32_MAX;
}
return (int) ms;
}
/* qemu implementation of g_poll which uses a nanosecond timeout but is
* otherwise identical to g_poll
*/
int qemu_poll_ns(GPollFD *fds, guint nfds, int64_t timeout)
{
#ifdef CONFIG_PPOLL
if (timeout < 0) {
return ppoll((struct pollfd *)fds, nfds, NULL, NULL);
} else {
struct timespec ts;
int64_t tvsec = timeout / 1000000000LL;
/* Avoid possibly overflowing and specifying a negative number of
* seconds, which would turn a very long timeout into a busy-wait.
*/
if (tvsec > (int64_t)INT32_MAX) {
tvsec = INT32_MAX;
}
ts.tv_sec = tvsec;
ts.tv_nsec = timeout % 1000000000LL;
return ppoll((struct pollfd *)fds, nfds, &ts, NULL);
}
#else
return g_poll(fds, nfds, qemu_timeout_ns_to_ms(timeout));
#endif
}
void timer_init_tl(QEMUTimer *ts,
QEMUTimerList *timer_list, int scale,
QEMUTimerCB *cb, void *opaque)
{
ts->timer_list = timer_list;
ts->cb = cb;
ts->opaque = opaque;
ts->scale = scale;
ts->expire_time = -1;
}
void timer_deinit(QEMUTimer *ts)
{
assert(ts->expire_time == -1);
ts->timer_list = NULL;
}
static void timer_del_locked(QEMUTimerList *timer_list, QEMUTimer *ts)
{
QEMUTimer **pt, *t;
ts->expire_time = -1;
pt = &timer_list->active_timers;
for(;;) {
t = *pt;
if (!t)
break;
if (t == ts) {
atomic_set(pt, t->next);
break;
}
pt = &t->next;
}
}
static bool timer_mod_ns_locked(QEMUTimerList *timer_list,
QEMUTimer *ts, int64_t expire_time)
{
QEMUTimer **pt, *t;
/* add the timer in the sorted list */
pt = &timer_list->active_timers;
for (;;) {
t = *pt;
if (!timer_expired_ns(t, expire_time)) {
break;
}
pt = &t->next;
}
ts->expire_time = MAX(expire_time, 0);
ts->next = *pt;
atomic_set(pt, ts);
return pt == &timer_list->active_timers;
}
static void timerlist_rearm(QEMUTimerList *timer_list)
{
/* Interrupt execution to force deadline recalculation. */
if (timer_list->clock->type == QEMU_CLOCK_VIRTUAL) {
qemu_start_warp_timer();
}
timerlist_notify(timer_list);
}
/* stop a timer, but do not dealloc it */
void timer_del(QEMUTimer *ts)
{
QEMUTimerList *timer_list = ts->timer_list;
if (timer_list) {
qemu_mutex_lock(&timer_list->active_timers_lock);
timer_del_locked(timer_list, ts);
qemu_mutex_unlock(&timer_list->active_timers_lock);
}
}
/* modify the current timer so that it will be fired when current_time
>= expire_time. The corresponding callback will be called. */
void timer_mod_ns(QEMUTimer *ts, int64_t expire_time)
{
QEMUTimerList *timer_list = ts->timer_list;
bool rearm;
qemu_mutex_lock(&timer_list->active_timers_lock);
timer_del_locked(timer_list, ts);
rearm = timer_mod_ns_locked(timer_list, ts, expire_time);
qemu_mutex_unlock(&timer_list->active_timers_lock);
if (rearm) {
timerlist_rearm(timer_list);
}
}
/* modify the current timer so that it will be fired when current_time
>= expire_time or the current deadline, whichever comes earlier.
The corresponding callback will be called. */
void timer_mod_anticipate_ns(QEMUTimer *ts, int64_t expire_time)
{
QEMUTimerList *timer_list = ts->timer_list;
bool rearm;
qemu_mutex_lock(&timer_list->active_timers_lock);
if (ts->expire_time == -1 || ts->expire_time > expire_time) {
if (ts->expire_time != -1) {
timer_del_locked(timer_list, ts);
}
rearm = timer_mod_ns_locked(timer_list, ts, expire_time);
} else {
rearm = false;
}
qemu_mutex_unlock(&timer_list->active_timers_lock);
if (rearm) {
timerlist_rearm(timer_list);
}
}
void timer_mod(QEMUTimer *ts, int64_t expire_time)
{
timer_mod_ns(ts, expire_time * ts->scale);
}
void timer_mod_anticipate(QEMUTimer *ts, int64_t expire_time)
{
timer_mod_anticipate_ns(ts, expire_time * ts->scale);
}
bool timer_pending(QEMUTimer *ts)
{
return ts->expire_time >= 0;
}
bool timer_expired(QEMUTimer *timer_head, int64_t current_time)
{
return timer_expired_ns(timer_head, current_time * timer_head->scale);
}
bool timerlist_run_timers(QEMUTimerList *timer_list)
{
QEMUTimer *ts;
int64_t current_time;
bool progress = false;
QEMUTimerCB *cb;
void *opaque;
if (!atomic_read(&timer_list->active_timers)) {
return false;
}
qemu_event_reset(&timer_list->timers_done_ev);
if (!timer_list->clock->enabled) {
goto out;
}
switch (timer_list->clock->type) {
case QEMU_CLOCK_REALTIME:
break;
default:
case QEMU_CLOCK_VIRTUAL:
if (!replay_checkpoint(CHECKPOINT_CLOCK_VIRTUAL)) {
goto out;
}
break;
case QEMU_CLOCK_HOST:
if (!replay_checkpoint(CHECKPOINT_CLOCK_HOST)) {
goto out;
}
break;
case QEMU_CLOCK_VIRTUAL_RT:
if (!replay_checkpoint(CHECKPOINT_CLOCK_VIRTUAL_RT)) {
goto out;
}
break;
}
current_time = qemu_clock_get_ns(timer_list->clock->type);
for(;;) {
qemu_mutex_lock(&timer_list->active_timers_lock);
ts = timer_list->active_timers;
if (!timer_expired_ns(ts, current_time)) {
qemu_mutex_unlock(&timer_list->active_timers_lock);
break;
}
/* remove timer from the list before calling the callback */
timer_list->active_timers = ts->next;
ts->next = NULL;
ts->expire_time = -1;
cb = ts->cb;
opaque = ts->opaque;
qemu_mutex_unlock(&timer_list->active_timers_lock);
/* run the callback (the timer list can be modified) */
cb(opaque);
progress = true;
}
out:
qemu_event_set(&timer_list->timers_done_ev);
return progress;
}
bool qemu_clock_run_timers(QEMUClockType type)
{
return timerlist_run_timers(main_loop_tlg.tl[type]);
}
void timerlistgroup_init(QEMUTimerListGroup *tlg,
QEMUTimerListNotifyCB *cb, void *opaque)
{
QEMUClockType type;
for (type = 0; type < QEMU_CLOCK_MAX; type++) {
tlg->tl[type] = timerlist_new(type, cb, opaque);
}
}
void timerlistgroup_deinit(QEMUTimerListGroup *tlg)
{
QEMUClockType type;
for (type = 0; type < QEMU_CLOCK_MAX; type++) {
timerlist_free(tlg->tl[type]);
}
}
bool timerlistgroup_run_timers(QEMUTimerListGroup *tlg)
{
QEMUClockType type;
bool progress = false;
for (type = 0; type < QEMU_CLOCK_MAX; type++) {
progress |= timerlist_run_timers(tlg->tl[type]);
}
return progress;
}
int64_t timerlistgroup_deadline_ns(QEMUTimerListGroup *tlg)
{
int64_t deadline = -1;
QEMUClockType type;
bool play = replay_mode == REPLAY_MODE_PLAY;
for (type = 0; type < QEMU_CLOCK_MAX; type++) {
if (qemu_clock_use_for_deadline(type)) {
if (!play || type == QEMU_CLOCK_REALTIME) {
deadline = qemu_soonest_timeout(deadline,
timerlist_deadline_ns(tlg->tl[type]));
} else {
/* Read clock from the replay file and
do not calculate the deadline, based on virtual clock. */
qemu_clock_get_ns(type);
}
}
}
return deadline;
}
int64_t qemu_clock_get_ns(QEMUClockType type)
{
int64_t now, last;
QEMUClock *clock = qemu_clock_ptr(type);
switch (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:
now = REPLAY_CLOCK(REPLAY_CLOCK_HOST, get_clock_realtime());
last = clock->last;
clock->last = now;
if (now < last || now > (last + get_max_clock_jump())) {
notifier_list_notify(&clock->reset_notifiers, &now);
}
return now;
case QEMU_CLOCK_VIRTUAL_RT:
return REPLAY_CLOCK(REPLAY_CLOCK_VIRTUAL_RT, cpu_get_clock());
}
}
void qemu_clock_register_reset_notifier(QEMUClockType type,
Notifier *notifier)
{
QEMUClock *clock = qemu_clock_ptr(type);
notifier_list_add(&clock->reset_notifiers, notifier);
}
void qemu_clock_unregister_reset_notifier(QEMUClockType type,
Notifier *notifier)
{
notifier_remove(notifier);
}
void init_clocks(QEMUTimerListNotifyCB *notify_cb)
{
QEMUClockType type;
for (type = 0; type < QEMU_CLOCK_MAX; type++) {
qemu_clock_init(type, notify_cb);
}
#ifdef CONFIG_PRCTL_PR_SET_TIMERSLACK
prctl(PR_SET_TIMERSLACK, 1, 0, 0, 0);
#endif
}
uint64_t timer_expire_time_ns(QEMUTimer *ts)
{
return timer_pending(ts) ? ts->expire_time : -1;
}
bool qemu_clock_run_all_timers(void)
{
bool progress = false;
QEMUClockType type;
for (type = 0; type < QEMU_CLOCK_MAX; type++) {
if (qemu_clock_use_for_deadline(type)) {
progress |= qemu_clock_run_timers(type);
}
}
return progress;
}