arch/x86/kernel/cpu/aperfmperf.c

   1 /*
   2  * x86 APERF/MPERF KHz calculation for
   3  * /sys/.../cpufreq/scaling_cur_freq
   4  *
   5  * Copyright (C) 2017 Intel Corp.
   6  * Author: Len Brown <len.brown@intel.com>
   7  *
   8  * This file is licensed under GPLv2.
   9  */
  10
  11 #include <linux/jiffies.h>
  12 #include <linux/math64.h>
  13 #include <linux/percpu.h>
  14 #include <linux/smp.h>
  15
  16 struct aperfmperf_sample {
  17         unsigned int    khz;
  18         unsigned long   jiffies;
  19         u64     aperf;
  20         u64     mperf;
  21 };
  22
  23 static DEFINE_PER_CPU(struct aperfmperf_sample, samples);
  24
  25 /*
  26  * aperfmperf_snapshot_khz()
  27  * On the current CPU, snapshot APERF, MPERF, and jiffies
  28  * unless we already did it within 10ms
  29  * calculate kHz, save snapshot
  30  */
  31 static void aperfmperf_snapshot_khz(void *dummy)
  32 {
  33         u64 aperf, aperf_delta;
  34         u64 mperf, mperf_delta;
  35         struct aperfmperf_sample *s = this_cpu_ptr(&samples);
  36
  37         /* Don't bother re-computing within 10 ms */
  38         if (time_before(jiffies, s->jiffies + HZ/100))
  39                 return;
  40
  41         rdmsrl(MSR_IA32_APERF, aperf);
  42         rdmsrl(MSR_IA32_MPERF, mperf);
  43
  44         aperf_delta = aperf - s->aperf;
  45         mperf_delta = mperf - s->mperf;
  46
  47         /*
  48          * There is no architectural guarantee that MPERF
  49          * increments faster than we can read it.
  50          */
  51         if (mperf_delta == 0)
  52                 return;
  53
  54         /*
  55          * if (cpu_khz * aperf_delta) fits into ULLONG_MAX, then
  56          *      khz = (cpu_khz * aperf_delta) / mperf_delta
  57          */
  58         if (div64_u64(ULLONG_MAX, cpu_khz) > aperf_delta)
  59                 s->khz = div64_u64((cpu_khz * aperf_delta), mperf_delta);
  60         else    /* khz = aperf_delta / (mperf_delta / cpu_khz) */
  61                 s->khz = div64_u64(aperf_delta,
  62                         div64_u64(mperf_delta, cpu_khz));
  63         s->jiffies = jiffies;
  64         s->aperf = aperf;
  65         s->mperf = mperf;
  66 }
  67
  68 unsigned int arch_freq_get_on_cpu(int cpu)
  69 {
  70         if (!cpu_khz)
  71                 return 0;
  72
  73         if (!static_cpu_has(X86_FEATURE_APERFMPERF))
  74                 return 0;
  75
  76         smp_call_function_single(cpu, aperfmperf_snapshot_khz, NULL, 1);
  77
  78         return per_cpu(samples.khz, cpu);
  79 }