'Called periodically to update node utilization metrics.'

def update_performance_cache(self):

    if (not self.zapi_client.features.SYSTEM_METRICS):
        return
    counters = self._get_node_utilization_counters()
    if (not counters):
        return
    self.performance_counters.append(counters)
    self.performance_counters = self.performance_counters[(-10):]
    if (len(self.performance_counters) < 2):
        self.utilization = perf_base.DEFAULT_UTILIZATION
    else:
        self.utilization = self._get_node_utilization(self.performance_counters[0], self.performance_counters[(-1)], self.node_name)
