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 set function and provide a percentage
of throttle time.
Signed-off-by: Jason J. Herne <jjhe...@linux.vnet.ibm.com>
Reviewed-by: Matthew Rosato <mjros...@linux.vnet.ibm.com>
---
cpus.c | 66 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
include/qom/cpu.h | 38 ++++++++++++++++++++++++++++++++
2 files changed, 104 insertions(+)
diff --git a/cpus.c b/cpus.c
index de6469f..6f86da0 100644
--- a/cpus.c
+++ b/cpus.c
@@ -68,6 +68,14 @@ static CPUState *next_cpu;
int64_t max_delay;
int64_t max_advance;
+/* vcpu throttling controls */
+static QEMUTimer *throttle_timer;
+static unsigned int throttle_percentage;
+
+#define CPU_THROTTLE_PCT_MIN 1
+#define CPU_THROTTLE_PCT_MAX 99
+#define CPU_THROTTLE_TIMESLICE 10
+
bool cpu_is_stopped(CPUState *cpu)
{
return cpu->stopped || !runstate_is_running();
@@ -486,10 +494,68 @@ static const VMStateDescription vmstate_timers = {
}
};
+static void cpu_throttle_thread(void *opaque)
+{
+ double pct = (double)throttle_percentage/100;
+ double throttle_ratio = pct / (1 - pct);
+ long sleeptime_ms = (long)(throttle_ratio * CPU_THROTTLE_TIMESLICE);
+
+ if (!throttle_percentage) {
+ return;
+ }
+
+ qemu_mutex_unlock_iothread();
+ g_usleep(sleeptime_ms * 1000); /* Convert ms to us for usleep call */
+ qemu_mutex_lock_iothread();
+}
+
+static void cpu_throttle_timer_tick(void *opaque)
+{
+ CPUState *cpu;
+
+ /* Stop the timer if needed */
+ if (!throttle_percentage) {
+ return;
+ }
+ CPU_FOREACH(cpu) {
+ async_run_on_cpu(cpu, cpu_throttle_thread, NULL);
+ }
+
+ timer_mod(throttle_timer, qemu_clock_get_ms(QEMU_CLOCK_VIRTUAL_RT) +
+ CPU_THROTTLE_TIMESLICE);
+}
+
+void cpu_throttle_set(int new_throttle_pct)
+{
+ /* Ensure throttle percentage is within valid range */
+ new_throttle_pct = MIN(new_throttle_pct, CPU_THROTTLE_PCT_MAX);
+ throttle_percentage = MAX(new_throttle_pct, CPU_THROTTLE_PCT_MIN);
+
+ timer_mod(throttle_timer, qemu_clock_get_ms(QEMU_CLOCK_VIRTUAL_RT) +
+ CPU_THROTTLE_TIMESLICE);
+}
+
+void cpu_throttle_stop(void)
+{
+ throttle_percentage = 0;
+}
+
+bool cpu_throttle_active(void)
+{
+ return (throttle_percentage != 0);
+}
+
+int cpu_throttle_get_percentage(void)
+{
+ return throttle_percentage;
+}
+
void cpu_ticks_init(void)
{
seqlock_init(&timers_state.vm_clock_seqlock, NULL);
vmstate_register(NULL, 0, &vmstate_timers, &timers_state);
+ throttle_timer = timer_new_ms(QEMU_CLOCK_VIRTUAL_RT,
+ cpu_throttle_timer_tick, NULL);
}
void configure_icount(QemuOpts *opts, Error **errp)
diff --git a/include/qom/cpu.h b/include/qom/cpu.h
index 39f0f19..56eb964 100644
--- a/include/qom/cpu.h
+++ b/include/qom/cpu.h
@@ -553,6 +553,44 @@ CPUState *qemu_get_cpu(int index);
*/
bool cpu_exists(int64_t id);
+/**
+ * cpu_throttle_set:
+ * @new_throttle_pct: Percent of sleep time to running time.
+ * Valid range is 1 to 99.
+ *
+ * Throttles all vcpus by forcing them to sleep for the given percentage of
+ * time. A throttle_percentage of 50 corresponds to a 50% duty cycle roughly.
+ * (example: 10ms sleep for every 10ms awake).
+ *
+ * cpu_throttle_set can be called as needed to adjust new_throttle_pct.
+ * Once the throttling starts, it will remain in effect until cpu_throttle_stop
+ * is called.
+ */
+void cpu_throttle_set(int new_throttle_pct);
+
+/**
+ * cpu_throttle_stop:
+ *
+ * Stops the vcpu throttling started by cpu_throttle_set.
+ */
+void cpu_throttle_stop(void);
+
+/**
+ * cpu_throttle_active:
+ *
+ * Returns %true if the vcpus are currently being throttled, %false otherwise.
+ */
+bool cpu_throttle_active(void);
+
+/**
+ * cpu_throttle_get_percentage:
+ *
+ * Returns the vcpu throttle percentage. See cpu_throttle_set for details.
+ *
+ * Returns The throttle percentage in range 1 to 99.
+ */
+int cpu_throttle_get_percentage(void);
+
#ifndef CONFIG_USER_ONLY
typedef void (*CPUInterruptHandler)(CPUState *, int);
--
1.9.1
