Provide a method to throttle guest cpu execution. CPUState is augmented with
timeout controls and throttle start/stop functions. To throttle the guest cpu
the caller simply has to call the throttle start function and provide a ratio of
sleep time to normal execution time.
Signed-off-by: Jason J. Herne <address@hidden>
Reviewed-by: Matthew Rosato <address@hidden>
---
cpus.c | 62 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
include/qom/cpu.h | 46 +++++++++++++++++++++++++++++++++++++++++
2 files changed, 108 insertions(+)
diff --git a/cpus.c b/cpus.c
index de6469f..7568357 100644
--- a/cpus.c
+++ b/cpus.c
@@ -64,6 +64,9 @@
#endif /* CONFIG_LINUX */
+/* Number of ms between cpu throttle operations */
+#define CPU_THROTTLE_TIMESLICE 10
+
static CPUState *next_cpu;
int64_t max_delay;
int64_t max_advance;
@@ -919,6 +922,65 @@ static void qemu_kvm_wait_io_event(CPUState *cpu)
qemu_wait_io_event_common(cpu);
}
+static void cpu_throttle_thread(void *opq)
+{
+ CPUState *cpu = (CPUState *)opq;
+ long sleeptime_ms = (long)(cpu->throttle_ratio * CPU_THROTTLE_TIMESLICE);
+
+ /* Stop the timer if needed */
+ if (cpu->throttle_timer_stop) {
+ timer_del(cpu->throttle_timer);
+ timer_free(cpu->throttle_timer);
+ cpu->throttle_timer = NULL;
+ return;
+ }
+
+ qemu_mutex_unlock_iothread();
+ g_usleep(sleeptime_ms * 1000); /* Convert ms to us for usleep call */
+ qemu_mutex_lock_iothread();
+
+ timer_mod(cpu->throttle_timer, qemu_clock_get_ms(QEMU_CLOCK_REALTIME) +
+ CPU_THROTTLE_TIMESLICE);
+}
+
+static void cpu_throttle_timer_pop(void *opq)
+{
+ CPUState *cpu = (CPUState *)opq;
+
+ async_run_on_cpu(cpu, cpu_throttle_thread, cpu);
+}
+
+void cpu_throttle_start(CPUState *cpu, float throttle_ratio)
+{
+ assert(throttle_ratio > 0);
+ cpu->throttle_ratio = throttle_ratio;
+
+ if (!cpu_throttle_active(cpu)) {
+ cpu->throttle_timer = timer_new_ms(QEMU_CLOCK_REALTIME,
+ cpu_throttle_timer_pop, cpu);
+ timer_mod(cpu->throttle_timer, qemu_clock_get_ms(QEMU_CLOCK_REALTIME) +
+ CPU_THROTTLE_TIMESLICE);
+ cpu->throttle_timer_stop = false;
+ }
+}
+
+void cpu_throttle_stop(CPUState *cpu)
+{
+ assert(cpu_throttle_active(cpu));
+ cpu->throttle_timer_stop = true;
+}
+
+bool cpu_throttle_active(CPUState *cpu)
+{
+ return (cpu->throttle_timer != NULL);
+}
+
+float cpu_throttle_get_ratio(CPUState *cpu)
+{
+ assert(cpu_throttle_active(cpu));
+ return cpu->throttle_ratio;
+}
+
static void *qemu_kvm_cpu_thread_fn(void *arg)
{
CPUState *cpu = arg;
diff --git a/include/qom/cpu.h b/include/qom/cpu.h
index 39f0f19..9d16e6a 100644
--- a/include/qom/cpu.h
+++ b/include/qom/cpu.h
@@ -310,6 +310,11 @@ struct CPUState {
uint32_t can_do_io;
int32_t exception_index; /* used by m68k TCG */
+ /* vcpu throttling controls */
+ QEMUTimer *throttle_timer;
+ bool throttle_timer_stop;
+ float throttle_ratio;
+
/* Note that this is accessed at the start of every TB via a negative
offset from AREG0. Leave this field at the end so as to make the
(absolute value) offset as small as possible. This reduces code
@@ -553,6 +558,47 @@ CPUState *qemu_get_cpu(int index);
*/
bool cpu_exists(int64_t id);
+/**
+ * cpu_throttle_start:
+ * @cpu: The vcpu to throttle
+ *
+ * Throttles a vcpu by forcing it to sleep. The duration of the sleep is a
+ * ratio of sleep time to running time. A ratio of 1.0 corresponds to a 50%
+ * duty cycle (example: 10ms sleep for every 10ms awake).
+ *
+ * cpu_throttle_start can be called as needed to adjust the throttle ratio.
+ * Once the throttling starts, it will remain in effect until cpu_throttle_stop
+ * is called.
+ */
+void cpu_throttle_start(CPUState *cpu, float throttle_ratio);
+
+/**
+ * cpu_throttle_stop:
+ * @cpu: The vcpu to stop throttling
+ *
+ * Stops the vcpu throttling started by cpu_throttle_start.
+ */
+void cpu_throttle_stop(CPUState *cpu);
+
+/**
+ * cpu_throttle_active:
+ * @cpu: The vcpu to check
+ *
+ * Returns %true if this vcpu is currently being throttled, %false otherwise.
+ */
+bool cpu_throttle_active(CPUState *cpu);
+
+/**
+ * cpu_throttle_get_ratio:
+ * @cpu: The vcpu whose throttle ratio to return.
+ *
+ * Returns the ratio being used to throttle this vcpu. See cpu_throttle_start
+ * for details.
+ *
+ * Returns The ratio being used to throttle this vcpu.
+ */
+float cpu_throttle_get_ratio(CPUState *cpu);
+
#ifndef CONFIG_USER_ONLY
typedef void (*CPUInterruptHandler)(CPUState *, int);
--
1.9.1