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 } 80