#include <linux/kernel.h>
  #include <linux/smp.h>
  #include <linux/module.h>
  #include <linux/init.h>
  #include <linux/cpufreq.h>
  #include <linux/slab.h>
  
  #include "mperf.h"
  
  static DEFINE_PER_CPU(struct aperfmperf, acfreq_old_perf);
  
  /* Called via smp_call_function_single(), on the target CPU */
  static void read_measured_perf_ctrs(void *_cur)
  {
  	struct aperfmperf *am = _cur;
  
  	get_aperfmperf(am);
  }
  
  /*
   * Return the measured active (C0) frequency on this CPU since last call
   * to this function.
   * Input: cpu number
   * Return: Average CPU frequency in terms of max frequency (zero on error)
   *
   * We use IA32_MPERF and IA32_APERF MSRs to get the measured performance
   * over a period of time, while CPU is in C0 state.
   * IA32_MPERF counts at the rate of max advertised frequency
   * IA32_APERF counts at the rate of actual CPU frequency
   * Only IA32_APERF/IA32_MPERF ratio is architecturally defined and
   * no meaning should be associated with absolute values of these MSRs.
   */
  unsigned int cpufreq_get_measured_perf(struct cpufreq_policy *policy,
  					unsigned int cpu)
  {
  	struct aperfmperf perf;
  	unsigned long ratio;
  	unsigned int retval;
  
  	if (smp_call_function_single(cpu, read_measured_perf_ctrs, &perf, 1))
  		return 0;
  
  	ratio = calc_aperfmperf_ratio(&per_cpu(acfreq_old_perf, cpu), &perf);
  	per_cpu(acfreq_old_perf, cpu) = perf;
  
  	retval = (policy->cpuinfo.max_freq * ratio) >> APERFMPERF_SHIFT;
  
  	return retval;
  }
  EXPORT_SYMBOL_GPL(cpufreq_get_measured_perf);
  MODULE_LICENSE("GPL");