1 // SPDX-License-Identifier: GPL-2.0-only 2 /* 3 * x86 APERF/MPERF KHz calculation for 4 * /sys/.../cpufreq/scaling_cur_freq 5 * 6 * Copyright (C) 2017 Intel Corp. 7 * Author: Len Brown <len.brown@intel.com> 8 */ 9 10 #include <linux/delay.h> 11 #include <linux/ktime.h> 12 #include <linux/math64.h> 13 #include <linux/percpu.h> 14 #include <linux/cpufreq.h> 15 #include <linux/smp.h> 16 #include <linux/sched/isolation.h> 17 #include <linux/rcupdate.h> 18 19 #include "cpu.h" 20 21 struct aperfmperf_sample { 22 unsigned int khz; 23 atomic_t scfpending; 24 ktime_t time; 25 u64 aperf; 26 u64 mperf; 27 }; 28 29 static DEFINE_PER_CPU(struct aperfmperf_sample, samples); 30 31 #define APERFMPERF_CACHE_THRESHOLD_MS 10 32 #define APERFMPERF_REFRESH_DELAY_MS 10 33 #define APERFMPERF_STALE_THRESHOLD_MS 1000 34 35 /* 36 * aperfmperf_snapshot_khz() 37 * On the current CPU, snapshot APERF, MPERF, and jiffies 38 * unless we already did it within 10ms 39 * calculate kHz, save snapshot 40 */ 41 static void aperfmperf_snapshot_khz(void *dummy) 42 { 43 u64 aperf, aperf_delta; 44 u64 mperf, mperf_delta; 45 struct aperfmperf_sample *s = this_cpu_ptr(&samples); 46 unsigned long flags; 47 48 local_irq_save(flags); 49 rdmsrl(MSR_IA32_APERF, aperf); 50 rdmsrl(MSR_IA32_MPERF, mperf); 51 local_irq_restore(flags); 52 53 aperf_delta = aperf - s->aperf; 54 mperf_delta = mperf - s->mperf; 55 56 /* 57 * There is no architectural guarantee that MPERF 58 * increments faster than we can read it. 59 */ 60 if (mperf_delta == 0) 61 return; 62 63 s->time = ktime_get(); 64 s->aperf = aperf; 65 s->mperf = mperf; 66 s->khz = div64_u64((cpu_khz * aperf_delta), mperf_delta); 67 atomic_set_release(&s->scfpending, 0); 68 } 69 70 static bool aperfmperf_snapshot_cpu(int cpu, ktime_t now, bool wait) 71 { 72 s64 time_delta = ktime_ms_delta(now, per_cpu(samples.time, cpu)); 73 struct aperfmperf_sample *s = per_cpu_ptr(&samples, cpu); 74 75 /* Don't bother re-computing within the cache threshold time. */ 76 if (time_delta < APERFMPERF_CACHE_THRESHOLD_MS) 77 return true; 78 79 if (!atomic_xchg(&s->scfpending, 1) || wait) 80 smp_call_function_single(cpu, aperfmperf_snapshot_khz, NULL, wait); 81 82 /* Return false if the previous iteration was too long ago. */ 83 return time_delta <= APERFMPERF_STALE_THRESHOLD_MS; 84 } 85 86 unsigned int aperfmperf_get_khz(int cpu) 87 { 88 if (!cpu_khz) 89 return 0; 90 91 if (!boot_cpu_has(X86_FEATURE_APERFMPERF)) 92 return 0; 93 94 if (!housekeeping_cpu(cpu, HK_TYPE_MISC)) 95 return 0; 96 97 if (rcu_is_idle_cpu(cpu)) 98 return 0; /* Idle CPUs are completely uninteresting. */ 99 100 aperfmperf_snapshot_cpu(cpu, ktime_get(), true); 101 return per_cpu(samples.khz, cpu); 102 } 103 104 void arch_freq_prepare_all(void) 105 { 106 ktime_t now = ktime_get(); 107 bool wait = false; 108 int cpu; 109 110 if (!cpu_khz) 111 return; 112 113 if (!boot_cpu_has(X86_FEATURE_APERFMPERF)) 114 return; 115 116 for_each_online_cpu(cpu) { 117 if (!housekeeping_cpu(cpu, HK_TYPE_MISC)) 118 continue; 119 if (rcu_is_idle_cpu(cpu)) 120 continue; /* Idle CPUs are completely uninteresting. */ 121 if (!aperfmperf_snapshot_cpu(cpu, now, false)) 122 wait = true; 123 } 124 125 if (wait) 126 msleep(APERFMPERF_REFRESH_DELAY_MS); 127 } 128 129 unsigned int arch_freq_get_on_cpu(int cpu) 130 { 131 struct aperfmperf_sample *s = per_cpu_ptr(&samples, cpu); 132 133 if (!cpu_khz) 134 return 0; 135 136 if (!boot_cpu_has(X86_FEATURE_APERFMPERF)) 137 return 0; 138 139 if (!housekeeping_cpu(cpu, HK_TYPE_MISC)) 140 return 0; 141 142 if (aperfmperf_snapshot_cpu(cpu, ktime_get(), true)) 143 return per_cpu(samples.khz, cpu); 144 145 msleep(APERFMPERF_REFRESH_DELAY_MS); 146 atomic_set(&s->scfpending, 1); 147 smp_mb(); /* ->scfpending before smp_call_function_single(). */ 148 smp_call_function_single(cpu, aperfmperf_snapshot_khz, NULL, 1); 149 150 return per_cpu(samples.khz, cpu); 151 } 152