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/delay.h>
  12 #include <linux/ktime.h>
  13 #include <linux/math64.h>
  14 #include <linux/percpu.h>
  15 #include <linux/smp.h>
  16
  17 struct aperfmperf_sample {
  18         unsigned int    khz;
  19         ktime_t time;
  20         u64     aperf;
  21         u64     mperf;
  22 };
  23
  24 static DEFINE_PER_CPU(struct aperfmperf_sample, samples);
  25
  26 #define APERFMPERF_CACHE_THRESHOLD_MS   10
  27 #define APERFMPERF_REFRESH_DELAY_MS     20
  28 #define APERFMPERF_STALE_THRESHOLD_MS   1000
  29
  30 /*
  31  * aperfmperf_snapshot_khz()
  32  * On the current CPU, snapshot APERF, MPERF, and jiffies
  33  * unless we already did it within 10ms
  34  * calculate kHz, save snapshot
  35  */
  36 static void aperfmperf_snapshot_khz(void *dummy)
  37 {
  38         u64 aperf, aperf_delta;
  39         u64 mperf, mperf_delta;
  40         struct aperfmperf_sample *s = this_cpu_ptr(&samples);
  41         ktime_t now = ktime_get();
  42         s64 time_delta = ktime_ms_delta(now, s->time);
  43
  44         /* Don't bother re-computing within the cache threshold time. */
  45         if (time_delta < APERFMPERF_CACHE_THRESHOLD_MS)
  46                 return;
  47
  48         rdmsrl(MSR_IA32_APERF, aperf);
  49         rdmsrl(MSR_IA32_MPERF, mperf);
  50
  51         aperf_delta = aperf - s->aperf;
  52         mperf_delta = mperf - s->mperf;
  53
  54         /*
  55          * There is no architectural guarantee that MPERF
  56          * increments faster than we can read it.
  57          */
  58         if (mperf_delta == 0)
  59                 return;
  60
  61         s->time = now;
  62         s->aperf = aperf;
  63         s->mperf = mperf;
  64
  65         /* If the previous iteration was too long ago, discard it. */
  66         if (time_delta > APERFMPERF_STALE_THRESHOLD_MS)
  67                 s->khz = 0;
  68         else
  69                 s->khz = div64_u64((cpu_khz * aperf_delta), mperf_delta);
  70 }
  71
  72 unsigned int arch_freq_get_on_cpu(int cpu)
  73 {
  74         unsigned int khz;
  75
  76         if (!cpu_khz)
  77                 return 0;
  78
  79         if (!static_cpu_has(X86_FEATURE_APERFMPERF))
  80                 return 0;
  81
  82         smp_call_function_single(cpu, aperfmperf_snapshot_khz, NULL, 1);
  83         khz = per_cpu(samples.khz, cpu);
  84         if (khz)
  85                 return khz;
  86
  87         msleep(APERFMPERF_REFRESH_DELAY_MS);
  88         smp_call_function_single(cpu, aperfmperf_snapshot_khz, NULL, 1);
  89
  90         return per_cpu(samples.khz, cpu);
  91 }