cpufreq: x86: Make scaling_cur_freq behave more as expected
[sfrench/cifs-2.6.git] / arch / x86 / kernel / cpu / aperfmperf.c
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 }