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 } 128