[mirror_ubuntu-artful-kernel.git] / arch / x86 / kernel / cpu / aperfmperf.c

/*
 * 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/delay.h>
#include <linux/ktime.h>
#include <linux/math64.h>
#include <linux/percpu.h>
#include <linux/smp.h>

struct aperfmperf_sample {
	unsigned int	khz;
	ktime_t	time;
	u64	aperf;
	u64	mperf;
};

static DEFINE_PER_CPU(struct aperfmperf_sample, samples);

#define APERFMPERF_CACHE_THRESHOLD_MS	10
#define APERFMPERF_REFRESH_DELAY_MS	20
#define APERFMPERF_STALE_THRESHOLD_MS	1000

/*
 * 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);
	ktime_t now = ktime_get();
	s64 time_delta = ktime_ms_delta(now, s->time);
	unsigned long flags;

	/* Don't bother re-computing within the cache threshold time. */
	if (time_delta < APERFMPERF_CACHE_THRESHOLD_MS)
		return;

	local_irq_save(flags);
	rdmsrl(MSR_IA32_APERF, aperf);
	rdmsrl(MSR_IA32_MPERF, mperf);
	local_irq_restore(flags);

	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;

	s->time = now;
	s->aperf = aperf;
	s->mperf = mperf;

	/* If the previous iteration was too long ago, discard it. */
	if (time_delta > APERFMPERF_STALE_THRESHOLD_MS)
		s->khz = 0;
	else
		s->khz = div64_u64((cpu_khz * aperf_delta), mperf_delta);
}

unsigned int arch_freq_get_on_cpu(int cpu)
{
	unsigned int khz;

	if (!cpu_khz)
		return 0;

	if (!static_cpu_has(X86_FEATURE_APERFMPERF))
		return 0;

	smp_call_function_single(cpu, aperfmperf_snapshot_khz, NULL, 1);
	khz = per_cpu(samples.khz, cpu);
	if (khz)
		return khz;

	msleep(APERFMPERF_REFRESH_DELAY_MS);
	smp_call_function_single(cpu, aperfmperf_snapshot_khz, NULL, 1);

	return per_cpu(samples.khz, cpu);
}
Commit	Line	Data
f8475cef LB	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
4815d3c5 RW	11	#include <linux/delay.h>
4815d3c5 RW	12	#include <linux/ktime.h>
f8475cef LB	13	#include <linux/math64.h>
	14	#include <linux/percpu.h>
	15	#include <linux/smp.h>
	16
	17	struct aperfmperf_sample {
	18	unsigned int khz;
4815d3c5	19	ktime_t time;
f8475cef LB	20	u64 aperf;
	21	u64 mperf;
	22	};
	23
	24	static DEFINE_PER_CPU(struct aperfmperf_sample, samples);
	25
4815d3c5 RW	26	#define APERFMPERF_CACHE_THRESHOLD_MS 10
	27	#define APERFMPERF_REFRESH_DELAY_MS 20
	28	#define APERFMPERF_STALE_THRESHOLD_MS 1000
	29
f8475cef LB	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);
4815d3c5 RW	41	ktime_t now = ktime_get();
4815d3c5 RW	42	s64 time_delta = ktime_ms_delta(now, s->time);
8e2f3bce	43	unsigned long flags;
f8475cef	44
4815d3c5 RW	45	/* Don't bother re-computing within the cache threshold time. */
4815d3c5 RW	46	if (time_delta < APERFMPERF_CACHE_THRESHOLD_MS)
f8475cef LB	47	return;
f8475cef LB	48
8e2f3bce	49	local_irq_save(flags);
f8475cef LB	50	rdmsrl(MSR_IA32_APERF, aperf);
f8475cef LB	51	rdmsrl(MSR_IA32_MPERF, mperf);
8e2f3bce	52	local_irq_restore(flags);
f8475cef LB	53
	54	aperf_delta = aperf - s->aperf;
	55	mperf_delta = mperf - s->mperf;
	56
	57	/*
	58	* There is no architectural guarantee that MPERF
	59	* increments faster than we can read it.
	60	*/
	61	if (mperf_delta == 0)
	62	return;
	63
4815d3c5	64	s->time = now;
f8475cef LB	65	s->aperf = aperf;
f8475cef LB	66	s->mperf = mperf;
4815d3c5 RW	67
	68	/* If the previous iteration was too long ago, discard it. */
	69	if (time_delta > APERFMPERF_STALE_THRESHOLD_MS)
	70	s->khz = 0;
	71	else
	72	s->khz = div64_u64((cpu_khz * aperf_delta), mperf_delta);
f8475cef LB	73	}
	74
	75	unsigned int arch_freq_get_on_cpu(int cpu)
	76	{
4815d3c5 RW	77	unsigned int khz;
4815d3c5 RW	78
f8475cef LB	79	if (!cpu_khz)
	80	return 0;
	81
	82	if (!static_cpu_has(X86_FEATURE_APERFMPERF))
	83	return 0;
	84
	85	smp_call_function_single(cpu, aperfmperf_snapshot_khz, NULL, 1);
4815d3c5 RW	86	khz = per_cpu(samples.khz, cpu);
	87	if (khz)
	88	return khz;
	89
	90	msleep(APERFMPERF_REFRESH_DELAY_MS);
	91	smp_call_function_single(cpu, aperfmperf_snapshot_khz, NULL, 1);
f8475cef LB	92
	93	return per_cpu(samples.khz, cpu);
	94	}