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tcg: add kick timer for single-threaded vCPU emulation 

Currently we rely on the side effect of the main loop grabbing the
iothread_mutex to give any long running basic block chains a kick to
ensure the next vCPU is scheduled. As this code is being re-factored and
rationalised we now do it explicitly here.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <rth@twiddle.net>
Reviewed-by: Pranith Kumar <bobby.prani@gmail.com>
This commit is contained in:
Alex Bennée 2017-02-23 18:29:09 +00:00
parent 8d4e9146b3
commit 6546706d28
1 changed files with 61 additions and 0 deletions
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61
cpus.c
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@ -767,6 +767,53 @@ void configure_icount(QemuOpts *opts, Error **errp)
NANOSECONDS_PER_SECOND / 10);
}
/***********************************************************/
/* TCG vCPU kick timer
*
* The kick timer is responsible for moving single threaded vCPU
* emulation on to the next vCPU. If more than one vCPU is running a
* timer event with force a cpu->exit so the next vCPU can get
* scheduled.
*
* The timer is removed if all vCPUs are idle and restarted again once
* idleness is complete.
*/
static QEMUTimer *tcg_kick_vcpu_timer;
static void qemu_cpu_kick_no_halt(void);
#define TCG_KICK_PERIOD (NANOSECONDS_PER_SECOND / 10)
static inline int64_t qemu_tcg_next_kick(void)
{
return qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + TCG_KICK_PERIOD;
}
static void kick_tcg_thread(void *opaque)
{
timer_mod(tcg_kick_vcpu_timer, qemu_tcg_next_kick());
qemu_cpu_kick_no_halt();
}
static void start_tcg_kick_timer(void)
{
if (!tcg_kick_vcpu_timer && CPU_NEXT(first_cpu)) {
tcg_kick_vcpu_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL,
kick_tcg_thread, NULL);
timer_mod(tcg_kick_vcpu_timer, qemu_tcg_next_kick());
}
}
static void stop_tcg_kick_timer(void)
{
if (tcg_kick_vcpu_timer) {
timer_del(tcg_kick_vcpu_timer);
tcg_kick_vcpu_timer = NULL;
}
}
/***********************************************************/
void hw_error(const char *fmt, ...)
{
@ -1021,9 +1068,12 @@ static void qemu_wait_io_event_common(CPUState *cpu)
static void qemu_tcg_wait_io_event(CPUState *cpu)
{
while (all_cpu_threads_idle()) {
stop_tcg_kick_timer();
qemu_cond_wait(cpu->halt_cond, &qemu_global_mutex);
}
start_tcg_kick_timer();
while (iothread_requesting_mutex) {
qemu_cond_wait(&qemu_io_proceeded_cond, &qemu_global_mutex);
}
@ -1223,6 +1273,15 @@ static void deal_with_unplugged_cpus(void)
}
}
/* Single-threaded TCG
*
* In the single-threaded case each vCPU is simulated in turn. If
* there is more than a single vCPU we create a simple timer to kick
* the vCPU and ensure we don't get stuck in a tight loop in one vCPU.
* This is done explicitly rather than relying on side-effects
* elsewhere.
*/
static void *qemu_tcg_cpu_thread_fn(void *arg)
{
CPUState *cpu = arg;
@ -1249,6 +1308,8 @@ static void *qemu_tcg_cpu_thread_fn(void *arg)
}
}
start_tcg_kick_timer();
/* process any pending work */
atomic_mb_set(&exit_request, 1);