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 } 92