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
18 #include "cpu.h"
19
20 struct aperfmperf_sample {
21 unsigned int khz;
22 ktime_t time;
23 u64 aperf;
24 u64 mperf;
25 };
26
27 static 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 */
aperfmperf_snapshot_khz(void * dummy)39 static 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
aperfmperf_snapshot_cpu(int cpu,ktime_t now,bool wait)67 static 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
aperfmperf_get_khz(int cpu)81 unsigned int aperfmperf_get_khz(int cpu)
82 {
83 if (!cpu_khz)
84 return 0;
85
86 if (!boot_cpu_has(X86_FEATURE_APERFMPERF))
87 return 0;
88
89 if (!housekeeping_cpu(cpu, HK_FLAG_MISC))
90 return 0;
91
92 aperfmperf_snapshot_cpu(cpu, ktime_get(), true);
93 return per_cpu(samples.khz, cpu);
94 }
95
arch_freq_prepare_all(void)96 void arch_freq_prepare_all(void)
97 {
98 ktime_t now = ktime_get();
99 bool wait = false;
100 int cpu;
101
102 if (!cpu_khz)
103 return;
104
105 if (!boot_cpu_has(X86_FEATURE_APERFMPERF))
106 return;
107
108 for_each_online_cpu(cpu) {
109 if (!housekeeping_cpu(cpu, HK_FLAG_MISC))
110 continue;
111 if (!aperfmperf_snapshot_cpu(cpu, now, false))
112 wait = true;
113 }
114
115 if (wait)
116 msleep(APERFMPERF_REFRESH_DELAY_MS);
117 }
118
arch_freq_get_on_cpu(int cpu)119 unsigned int arch_freq_get_on_cpu(int cpu)
120 {
121 if (!cpu_khz)
122 return 0;
123
124 if (!boot_cpu_has(X86_FEATURE_APERFMPERF))
125 return 0;
126
127 if (!housekeeping_cpu(cpu, HK_FLAG_MISC))
128 return 0;
129
130 if (aperfmperf_snapshot_cpu(cpu, ktime_get(), true))
131 return per_cpu(samples.khz, cpu);
132
133 msleep(APERFMPERF_REFRESH_DELAY_MS);
134 smp_call_function_single(cpu, aperfmperf_snapshot_khz, NULL, 1);
135
136 return per_cpu(samples.khz, cpu);
137 }
138
