cpu: Provide vcpu throttling interface
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 <jjherne@linux.vnet.ibm.com>
Reviewed-by: Matthew Rosato <mjrosato@linux.vnet.ibm.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
diff --git a/cpus.c b/cpus.c
index dddd056..d44c0ed 100644
--- a/cpus.c
+++ b/cpus.c
@@ -69,6 +69,14 @@
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_NS 10000000
+
bool cpu_is_stopped(CPUState *cpu)
{
return cpu->stopped || !runstate_is_running();
@@ -505,10 +513,80 @@
}
};
+static void cpu_throttle_thread(void *opaque)
+{
+ CPUState *cpu = opaque;
+ double pct;
+ double throttle_ratio;
+ long sleeptime_ns;
+
+ if (!cpu_throttle_get_percentage()) {
+ return;
+ }
+
+ pct = (double)cpu_throttle_get_percentage()/100;
+ throttle_ratio = pct / (1 - pct);
+ sleeptime_ns = (long)(throttle_ratio * CPU_THROTTLE_TIMESLICE_NS);
+
+ qemu_mutex_unlock_iothread();
+ atomic_set(&cpu->throttle_thread_scheduled, 0);
+ g_usleep(sleeptime_ns / 1000); /* Convert ns to us for usleep call */
+ qemu_mutex_lock_iothread();
+}
+
+static void cpu_throttle_timer_tick(void *opaque)
+{
+ CPUState *cpu;
+ double pct;
+
+ /* Stop the timer if needed */
+ if (!cpu_throttle_get_percentage()) {
+ return;
+ }
+ CPU_FOREACH(cpu) {
+ if (!atomic_xchg(&cpu->throttle_thread_scheduled, 1)) {
+ async_run_on_cpu(cpu, cpu_throttle_thread, cpu);
+ }
+ }
+
+ pct = (double)cpu_throttle_get_percentage()/100;
+ timer_mod(throttle_timer, qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL_RT) +
+ CPU_THROTTLE_TIMESLICE_NS / (1-pct));
+}
+
+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);
+ new_throttle_pct = MAX(new_throttle_pct, CPU_THROTTLE_PCT_MIN);
+
+ atomic_set(&throttle_percentage, new_throttle_pct);
+
+ timer_mod(throttle_timer, qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL_RT) +
+ CPU_THROTTLE_TIMESLICE_NS);
+}
+
+void cpu_throttle_stop(void)
+{
+ atomic_set(&throttle_percentage, 0);
+}
+
+bool cpu_throttle_active(void)
+{
+ return (cpu_throttle_get_percentage() != 0);
+}
+
+int cpu_throttle_get_percentage(void)
+{
+ return atomic_read(&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_ns(QEMU_CLOCK_VIRTUAL_RT,
+ cpu_throttle_timer_tick, NULL);
}
void configure_icount(QemuOpts *opts, Error **errp)
