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/cpufreq.h>
16#include <linux/smp.h>
17
18#include "cpu.h"
19
20struct aperfmperf_sample {
21 unsigned int khz;
22 ktime_t time;
23 u64 aperf;
24 u64 mperf;
25};
26
27static DEFINE_PER_CPU(struct aperfmperf_sample, samples);
28
29#define APERFMPERF_CACHE_THRESHOLD_MS 10
30#define APERFMPERF_REFRESH_DELAY_MS 10
31#define APERFMPERF_STALE_THRESHOLD_MS 1000
32
33/*
34 * aperfmperf_snapshot_khz()
35 * On the current CPU, snapshot APERF, MPERF, and jiffies
36 * unless we already did it within 10ms
37 * calculate kHz, save snapshot
38 */
39static void aperfmperf_snapshot_khz(void *dummy)
40{
41 u64 aperf, aperf_delta;
42 u64 mperf, mperf_delta;
43 struct aperfmperf_sample *s = this_cpu_ptr(&samples);
44 unsigned long flags;
45
46 local_irq_save(flags);
47 rdmsrl(MSR_IA32_APERF, aperf);
48 rdmsrl(MSR_IA32_MPERF, mperf);
49 local_irq_restore(flags);
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 = ktime_get();
62 s->aperf = aperf;
63 s->mperf = mperf;
64 s->khz = div64_u64((cpu_khz * aperf_delta), mperf_delta);
65}
66
67static bool aperfmperf_snapshot_cpu(int cpu, ktime_t now, bool wait)
68{
69 s64 time_delta = ktime_ms_delta(now, per_cpu(samples.time, cpu));
70
71 /* Don't bother re-computing within the cache threshold time. */
72 if (time_delta < APERFMPERF_CACHE_THRESHOLD_MS)
73 return true;
74
75 smp_call_function_single(cpu, aperfmperf_snapshot_khz, NULL, wait);
76
77 /* Return false if the previous iteration was too long ago. */
78 return time_delta <= APERFMPERF_STALE_THRESHOLD_MS;
79}
80
81unsigned int aperfmperf_get_khz(int cpu)
82{
83 if (!cpu_khz)
84 return 0;
85
86 if (!static_cpu_has(X86_FEATURE_APERFMPERF))
87 return 0;
88
89 aperfmperf_snapshot_cpu(cpu, ktime_get(), true);
90 return per_cpu(samples.khz, cpu);
91}
92
93void arch_freq_prepare_all(void)
94{
95 ktime_t now = ktime_get();
96 bool wait = false;
97 int cpu;
98
99 if (!cpu_khz)
100 return;
101
102 if (!static_cpu_has(X86_FEATURE_APERFMPERF))
103 return;
104
105 for_each_online_cpu(cpu)
106 if (!aperfmperf_snapshot_cpu(cpu, now, false))
107 wait = true;
108
109 if (wait)
110 msleep(APERFMPERF_REFRESH_DELAY_MS);
111}
112
113unsigned int arch_freq_get_on_cpu(int cpu)
114{
115 if (!cpu_khz)
116 return 0;
117
118 if (!static_cpu_has(X86_FEATURE_APERFMPERF))
119 return 0;
120
121 if (aperfmperf_snapshot_cpu(cpu, ktime_get(), true))
122 return per_cpu(samples.khz, cpu);
123
124 msleep(APERFMPERF_REFRESH_DELAY_MS);
125 smp_call_function_single(cpu, aperfmperf_snapshot_khz, NULL, 1);
126
127 return per_cpu(samples.khz, cpu);
128}
129