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>
---
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
---
cpus.c | 32 ++++++++++++++++++++++++++++++++
1 file changed, 32 insertions(+)
diff --git a/cpus.c b/cpus.c
index b5b45b8..8c49d6c 100644
--- a/cpus.c
+++ b/cpus.c
@@ -1185,9 +1185,34 @@ 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_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)
+{
+ QEMUTimer *self = *(QEMUTimer **) opaque;
+ timer_mod(self, qemu_tcg_next_kick());
+ qemu_cpu_kick_no_halt();
+}
+
static void *qemu_tcg_cpu_thread_fn(void *arg)
{
CPUState *cpu = arg;
+ QEMUTimer *kick_timer;
rcu_register_thread();
@@ -1211,6 +1236,13 @@ static void *qemu_tcg_cpu_thread_fn(void *arg)
}
}
+ /* Set to kick if we have to do more than one vCPU */
+ if (CPU_NEXT(first_cpu)) {
+ kick_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL, kick_tcg_thread,
+ &kick_timer);
+ timer_mod(kick_timer, qemu_tcg_next_kick());
+ }
+
/* process any pending work */
atomic_mb_set(&exit_request, 1);
--
2.7.4
