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/*
* x86 APERF/MPERF KHz calculation for
* /sys/.../cpufreq/scaling_cur_freq
*
* Copyright (C) 2017 Intel Corp.
* Author: Len Brown <len.brown@intel.com>
*
* This file is licensed under GPLv2.
*/
#include <linux/jiffies.h>
#include <linux/math64.h>
#include <linux/percpu.h>
#include <linux/smp.h>
struct aperfmperf_sample {
unsigned int khz;
unsigned long jiffies;
u64 aperf;
u64 mperf;
};
static DEFINE_PER_CPU(struct aperfmperf_sample, samples);
/*
* aperfmperf_snapshot_khz()
* On the current CPU, snapshot APERF, MPERF, and jiffies
* unless we already did it within 10ms
* calculate kHz, save snapshot
*/
static void aperfmperf_snapshot_khz(void *dummy)
{
u64 aperf, aperf_delta;
u64 mperf, mperf_delta;
struct aperfmperf_sample *s = this_cpu_ptr(&samples);
/* Don't bother re-computing within 10 ms */
if (time_before(jiffies, s->jiffies + HZ/100))
return;
rdmsrl(MSR_IA32_APERF, aperf);
rdmsrl(MSR_IA32_MPERF, mperf);
aperf_delta = aperf - s->aperf;
mperf_delta = mperf - s->mperf;
/*
* There is no architectural guarantee that MPERF
* increments faster than we can read it.
*/
if (mperf_delta == 0)
return;
/*
* if (cpu_khz * aperf_delta) fits into ULLONG_MAX, then
* khz = (cpu_khz * aperf_delta) / mperf_delta
*/
if (div64_u64(ULLONG_MAX, cpu_khz) > aperf_delta)
s->khz = div64_u64((cpu_khz * aperf_delta), mperf_delta);
else /* khz = aperf_delta / (mperf_delta / cpu_khz) */
s->khz = div64_u64(aperf_delta,
div64_u64(mperf_delta, cpu_khz));
s->jiffies = jiffies;
s->aperf = aperf;
s->mperf = mperf;
}
unsigned int arch_freq_get_on_cpu(int cpu)
{
if (!cpu_khz)
return 0;
if (!static_cpu_has(X86_FEATURE_APERFMPERF))
return 0;
smp_call_function_single(cpu, aperfmperf_snapshot_khz, NULL, 1);
return per_cpu(samples.khz, cpu);
}
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