drivers/cpufreq/mperf.c

   1 #include <linux/kernel.h>
   2 #include <linux/smp.h>
   3 #include <linux/module.h>
   4 #include <linux/init.h>
   5 #include <linux/cpufreq.h>
   6 #include <linux/slab.h>
   7
   8 #include "mperf.h"
   9
  10 static DEFINE_PER_CPU(struct aperfmperf, acfreq_old_perf);
  11
  12 /* Called via smp_call_function_single(), on the target CPU */
  13 static void read_measured_perf_ctrs(void *_cur)
  14 {
  15         struct aperfmperf *am = _cur;
  16
  17         get_aperfmperf(am);
  18 }
  19
  20 /*
  21  * Return the measured active (C0) frequency on this CPU since last call
  22  * to this function.
  23  * Input: cpu number
  24  * Return: Average CPU frequency in terms of max frequency (zero on error)
  25  *
  26  * We use IA32_MPERF and IA32_APERF MSRs to get the measured performance
  27  * over a period of time, while CPU is in C0 state.
  28  * IA32_MPERF counts at the rate of max advertised frequency
  29  * IA32_APERF counts at the rate of actual CPU frequency
  30  * Only IA32_APERF/IA32_MPERF ratio is architecturally defined and
  31  * no meaning should be associated with absolute values of these MSRs.
  32  */
  33 unsigned int cpufreq_get_measured_perf(struct cpufreq_policy *policy,
  34                                         unsigned int cpu)
  35 {
  36         struct aperfmperf perf;
  37         unsigned long ratio;
  38         unsigned int retval;
  39
  40         if (smp_call_function_single(cpu, read_measured_perf_ctrs, &perf, 1))
  41                 return 0;
  42
  43         ratio = calc_aperfmperf_ratio(&per_cpu(acfreq_old_perf, cpu), &perf);
  44         per_cpu(acfreq_old_perf, cpu) = perf;
  45
  46         retval = (policy->cpuinfo.max_freq * ratio) >> APERFMPERF_SHIFT;
  47
  48         return retval;
  49 }
  50 EXPORT_SYMBOL_GPL(cpufreq_get_measured_perf);
  51 MODULE_LICENSE("GPL");