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 #include "cpu.h"
  18
  19 struct aperfmperf_sample {
  20         unsigned int    khz;
  21         ktime_t time;
  22         u64     aperf;
  23         u64     mperf;
  24 };
  25
  26 static DEFINE_PER_CPU(struct aperfmperf_sample, samples);
  27
  28 #define APERFMPERF_CACHE_THRESHOLD_MS   10
  29 #define APERFMPERF_REFRESH_DELAY_MS     10
  30 #define APERFMPERF_STALE_THRESHOLD_MS   1000
  31
  32 /*
  33  * aperfmperf_snapshot_khz()
  34  * On the current CPU, snapshot APERF, MPERF, and jiffies
  35  * unless we already did it within 10ms
  36  * calculate kHz, save snapshot
  37  */
  38 static void aperfmperf_snapshot_khz(void *dummy)
  39 {
  40         u64 aperf, aperf_delta;
  41         u64 mperf, mperf_delta;
  42         struct aperfmperf_sample *s = this_cpu_ptr(&samples);
  43         unsigned long flags;
  44
  45         local_irq_save(flags);
  46         rdmsrl(MSR_IA32_APERF, aperf);
  47         rdmsrl(MSR_IA32_MPERF, mperf);
  48         local_irq_restore(flags);
  49
  50         aperf_delta = aperf - s->aperf;
  51         mperf_delta = mperf - s->mperf;
  52
  53         /*
  54          * There is no architectural guarantee that MPERF
  55          * increments faster than we can read it.
  56          */
  57         if (mperf_delta == 0)
  58                 return;
  59
  60         s->time = ktime_get();
  61         s->aperf = aperf;
  62         s->mperf = mperf;
  63         s->khz = div64_u64((cpu_khz * aperf_delta), mperf_delta);
  64 }
  65
  66 static bool aperfmperf_snapshot_cpu(int cpu, ktime_t now, bool wait)
  67 {
  68         s64 time_delta = ktime_ms_delta(now, per_cpu(samples.time, cpu));
  69
  70         /* Don't bother re-computing within the cache threshold time. */
  71         if (time_delta < APERFMPERF_CACHE_THRESHOLD_MS)
  72                 return true;
  73
  74         smp_call_function_single(cpu, aperfmperf_snapshot_khz, NULL, wait);
  75
  76         /* Return false if the previous iteration was too long ago. */
  77         return time_delta <= APERFMPERF_STALE_THRESHOLD_MS;
  78 }
  79
  80 unsigned int aperfmperf_get_khz(int cpu)
  81 {
  82         if (!cpu_khz)
  83                 return 0;
  84
  85         if (!static_cpu_has(X86_FEATURE_APERFMPERF))
  86                 return 0;
  87
  88         aperfmperf_snapshot_cpu(cpu, ktime_get(), true);
  89         return per_cpu(samples.khz, cpu);
  90 }
  91
  92 void arch_freq_prepare_all(void)
  93 {
  94         ktime_t now = ktime_get();
  95         bool wait = false;
  96         int cpu;
  97
  98         if (!cpu_khz)
  99                 return;
 100
 101         if (!static_cpu_has(X86_FEATURE_APERFMPERF))
 102                 return;
 103
 104         for_each_online_cpu(cpu)
 105                 if (!aperfmperf_snapshot_cpu(cpu, now, false))
 106                         wait = true;
 107
 108         if (wait)
 109                 msleep(APERFMPERF_REFRESH_DELAY_MS);
 110 }
 111
 112 unsigned int arch_freq_get_on_cpu(int cpu)
 113 {
 114         if (!cpu_khz)
 115                 return 0;
 116
 117         if (!static_cpu_has(X86_FEATURE_APERFMPERF))
 118                 return 0;
 119
 120         if (aperfmperf_snapshot_cpu(cpu, ktime_get(), true))
 121                 return per_cpu(samples.khz, cpu);
 122
 123         msleep(APERFMPERF_REFRESH_DELAY_MS);
 124         smp_call_function_single(cpu, aperfmperf_snapshot_khz, NULL, 1);
 125
 126         return per_cpu(samples.khz, cpu);
 127 }