2 * x86 APERF/MPERF KHz calculation for
3 * /sys/.../cpufreq/scaling_cur_freq
5 * Copyright (C) 2017 Intel Corp.
6 * Author: Len Brown <len.brown@intel.com>
8 * This file is licensed under GPLv2.
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>
17 struct aperfmperf_sample
{
24 static DEFINE_PER_CPU(struct aperfmperf_sample
, samples
);
26 #define APERFMPERF_CACHE_THRESHOLD_MS 10
27 #define APERFMPERF_REFRESH_DELAY_MS 20
28 #define APERFMPERF_STALE_THRESHOLD_MS 1000
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
36 static void aperfmperf_snapshot_khz(void *dummy
)
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
);
45 /* Don't bother re-computing within the cache threshold time. */
46 if (time_delta
< APERFMPERF_CACHE_THRESHOLD_MS
)
49 local_irq_save(flags
);
50 rdmsrl(MSR_IA32_APERF
, aperf
);
51 rdmsrl(MSR_IA32_MPERF
, mperf
);
52 local_irq_restore(flags
);
54 aperf_delta
= aperf
- s
->aperf
;
55 mperf_delta
= mperf
- s
->mperf
;
58 * There is no architectural guarantee that MPERF
59 * increments faster than we can read it.
68 /* If the previous iteration was too long ago, discard it. */
69 if (time_delta
> APERFMPERF_STALE_THRESHOLD_MS
)
72 s
->khz
= div64_u64((cpu_khz
* aperf_delta
), mperf_delta
);
75 unsigned int arch_freq_get_on_cpu(int cpu
)
82 if (!static_cpu_has(X86_FEATURE_APERFMPERF
))
85 smp_call_function_single(cpu
, aperfmperf_snapshot_khz
, NULL
, 1);
86 khz
= per_cpu(samples
.khz
, cpu
);
90 msleep(APERFMPERF_REFRESH_DELAY_MS
);
91 smp_call_function_single(cpu
, aperfmperf_snapshot_khz
, NULL
, 1);
93 return per_cpu(samples
.khz
, cpu
);