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.ben...@linaro.org>
Reviewed-by: Richard Henderson <r...@twiddle.net>
Reviewed-by: Pranith Kumar <bobby.pr...@gmail.com>
---
v2
- re-base fixes
- get_ticks_per_sec() -> NANOSECONDS_PER_SEC
v3
- add define for TCG_KICK_FREQ
- fix checkpatch warning
v4
- wrap next calc in inline qemu_tcg_next_kick() instead of macro
v5
- move all kick code into own section
- use global for timer
- add helper functions to start/stop timer
- stop timer when all cores paused
v7
- checkpatch > 80 char fix
---
cpus.c | 61 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 61 insertions(+)
diff --git a/cpus.c b/cpus.c
index c94b3307e5..9fe56c9a76 100644
--- a/cpus.c
+++ b/cpus.c
@@ -768,6 +768,53 @@ void configure_icount(QemuOpts *opts, Error **errp)
}
/***********************************************************/
+/* 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, ...)
{
va_list ap;
@@ -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);
--
2.11.0
