[mirror_ubuntu-bionic-kernel.git] / drivers / cpuidle / governors / menu.c

/*
 * menu.c - the menu idle governor
 *
 * Copyright (C) 2006-2007 Adam Belay <abelay@novell.com>
 * Copyright (C) 2009 Intel Corporation
 * Author:
 *        Arjan van de Ven <arjan@linux.intel.com>
 *
 * This code is licenced under the GPL version 2 as described
 * in the COPYING file that acompanies the Linux Kernel.
 */

#include <linux/kernel.h>
#include <linux/cpuidle.h>
#include <linux/pm_qos_params.h>
#include <linux/time.h>
#include <linux/ktime.h>
#include <linux/hrtimer.h>
#include <linux/tick.h>
#include <linux/sched.h>

#define BUCKETS 12
#define RESOLUTION 1024
#define DECAY 4
#define MAX_INTERESTING 50000

/*
 * Concepts and ideas behind the menu governor
 *
 * For the menu governor, there are 3 decision factors for picking a C
 * state:
 * 1) Energy break even point
 * 2) Performance impact
 * 3) Latency tolerance (from pmqos infrastructure)
 * These these three factors are treated independently.
 *
 * Energy break even point
 * -----------------------
 * C state entry and exit have an energy cost, and a certain amount of time in
 * the  C state is required to actually break even on this cost. CPUIDLE
 * provides us this duration in the "target_residency" field. So all that we
 * need is a good prediction of how long we'll be idle. Like the traditional
 * menu governor, we start with the actual known "next timer event" time.
 *
 * Since there are other source of wakeups (interrupts for example) than
 * the next timer event, this estimation is rather optimistic. To get a
 * more realistic estimate, a correction factor is applied to the estimate,
 * that is based on historic behavior. For example, if in the past the actual
 * duration always was 50% of the next timer tick, the correction factor will
 * be 0.5.
 *
 * menu uses a running average for this correction factor, however it uses a
 * set of factors, not just a single factor. This stems from the realization
 * that the ratio is dependent on the order of magnitude of the expected
 * duration; if we expect 500 milliseconds of idle time the likelihood of
 * getting an interrupt very early is much higher than if we expect 50 micro
 * seconds of idle time. A second independent factor that has big impact on
 * the actual factor is if there is (disk) IO outstanding or not.
 * (as a special twist, we consider every sleep longer than 50 milliseconds
 * as perfect; there are no power gains for sleeping longer than this)
 *
 * For these two reasons we keep an array of 12 independent factors, that gets
 * indexed based on the magnitude of the expected duration as well as the
 * "is IO outstanding" property.
 *
 * Limiting Performance Impact
 * ---------------------------
 * C states, especially those with large exit latencies, can have a real
 * noticable impact on workloads, which is not acceptable for most sysadmins,
 * and in addition, less performance has a power price of its own.
 *
 * As a general rule of thumb, menu assumes that the following heuristic
 * holds:
 *     The busier the system, the less impact of C states is acceptable
 *
 * This rule-of-thumb is implemented using a performance-multiplier:
 * If the exit latency times the performance multiplier is longer than
 * the predicted duration, the C state is not considered a candidate
 * for selection due to a too high performance impact. So the higher
 * this multiplier is, the longer we need to be idle to pick a deep C
 * state, and thus the less likely a busy CPU will hit such a deep
 * C state.
 *
 * Two factors are used in determing this multiplier:
 * a value of 10 is added for each point of "per cpu load average" we have.
 * a value of 5 points is added for each process that is waiting for
 * IO on this CPU.
 * (these values are experimentally determined)
 *
 * The load average factor gives a longer term (few seconds) input to the
 * decision, while the iowait value gives a cpu local instantanious input.
 * The iowait factor may look low, but realize that this is also already
 * represented in the system load average.
 *
 */

struct menu_device {
	int		last_state_idx;
	int             needs_update;

	unsigned int	expected_us;
	u64		predicted_us;
	unsigned int	measured_us;
	unsigned int	exit_us;
	unsigned int	bucket;
	u64		correction_factor[BUCKETS];
};


#define LOAD_INT(x) ((x) >> FSHIFT)
#define LOAD_FRAC(x) LOAD_INT(((x) & (FIXED_1-1)) * 100)

static int get_loadavg(void)
{
	unsigned long this = this_cpu_load();


	return LOAD_INT(this) * 10 + LOAD_FRAC(this) / 10;
}

static inline int which_bucket(unsigned int duration)
{
	int bucket = 0;

	/*
	 * We keep two groups of stats; one with no
	 * IO pending, one without.
	 * This allows us to calculate
	 * E(duration)|iowait
	 */
	if (nr_iowait_cpu())
		bucket = BUCKETS/2;

	if (duration < 10)
		return bucket;
	if (duration < 100)
		return bucket + 1;
	if (duration < 1000)
		return bucket + 2;
	if (duration < 10000)
		return bucket + 3;
	if (duration < 100000)
		return bucket + 4;
	return bucket + 5;
}

/*
 * Return a multiplier for the exit latency that is intended
 * to take performance requirements into account.
 * The more performance critical we estimate the system
 * to be, the higher this multiplier, and thus the higher
 * the barrier to go to an expensive C state.
 */
static inline int performance_multiplier(void)
{
	int mult = 1;

	/* for higher loadavg, we are more reluctant */

	mult += 2 * get_loadavg();

	/* for IO wait tasks (per cpu!) we add 5x each */
	mult += 10 * nr_iowait_cpu();

	return mult;
}

static DEFINE_PER_CPU(struct menu_device, menu_devices);

static void menu_update(struct cpuidle_device *dev);

/**
 * menu_select - selects the next idle state to enter
 * @dev: the CPU
 */
static int menu_select(struct cpuidle_device *dev)
{
	struct menu_device *data = &__get_cpu_var(menu_devices);
	int latency_req = pm_qos_requirement(PM_QOS_CPU_DMA_LATENCY);
	int i;
	int multiplier;

	data->last_state_idx = 0;
	data->exit_us = 0;

	if (data->needs_update) {
		menu_update(dev);
		data->needs_update = 0;
	}

	/* Special case when user has set very strict latency requirement */
	if (unlikely(latency_req == 0))
		return 0;

	/* determine the expected residency time, round up */
	data->expected_us =
	    DIV_ROUND_UP((u32)ktime_to_ns(tick_nohz_get_sleep_length()), 1000);


	data->bucket = which_bucket(data->expected_us);

	multiplier = performance_multiplier();

	/*
	 * if the correction factor is 0 (eg first time init or cpu hotplug
	 * etc), we actually want to start out with a unity factor.
	 */
	if (data->correction_factor[data->bucket] == 0)
		data->correction_factor[data->bucket] = RESOLUTION * DECAY;

	/* Make sure to round up for half microseconds */
	data->predicted_us = DIV_ROUND_CLOSEST(
		data->expected_us * data->correction_factor[data->bucket],
		RESOLUTION * DECAY);

	/*
	 * We want to default to C1 (hlt), not to busy polling
	 * unless the timer is happening really really soon.
	 */
	if (data->expected_us > 5)
		data->last_state_idx = CPUIDLE_DRIVER_STATE_START;


	/* find the deepest idle state that satisfies our constraints */
	for (i = CPUIDLE_DRIVER_STATE_START; i < dev->state_count; i++) {
		struct cpuidle_state *s = &dev->states[i];

		if (s->target_residency > data->predicted_us)
			break;
		if (s->exit_latency > latency_req)
			break;
		if (s->exit_latency * multiplier > data->predicted_us)
			break;
		data->exit_us = s->exit_latency;
		data->last_state_idx = i;
	}

	return data->last_state_idx;
}

/**
 * menu_reflect - records that data structures need update
 * @dev: the CPU
 *
 * NOTE: it's important to be fast here because this operation will add to
 *       the overall exit latency.
 */
static void menu_reflect(struct cpuidle_device *dev)
{
	struct menu_device *data = &__get_cpu_var(menu_devices);
	data->needs_update = 1;
}

/**
 * menu_update - attempts to guess what happened after entry
 * @dev: the CPU
 */
static void menu_update(struct cpuidle_device *dev)
{
	struct menu_device *data = &__get_cpu_var(menu_devices);
	int last_idx = data->last_state_idx;
	unsigned int last_idle_us = cpuidle_get_last_residency(dev);
	struct cpuidle_state *target = &dev->states[last_idx];
	unsigned int measured_us;
	u64 new_factor;

	/*
	 * Ugh, this idle state doesn't support residency measurements, so we
	 * are basically lost in the dark.  As a compromise, assume we slept
	 * for the whole expected time.
	 */
	if (unlikely(!(target->flags & CPUIDLE_FLAG_TIME_VALID)))
		last_idle_us = data->expected_us;


	measured_us = last_idle_us;

	/*
	 * We correct for the exit latency; we are assuming here that the
	 * exit latency happens after the event that we're interested in.
	 */
	if (measured_us > data->exit_us)
		measured_us -= data->exit_us;


	/* update our correction ratio */

	new_factor = data->correction_factor[data->bucket]
			* (DECAY - 1) / DECAY;

	if (data->expected_us > 0 && data->measured_us < MAX_INTERESTING)
		new_factor += RESOLUTION * measured_us / data->expected_us;
	else
		/*
		 * we were idle so long that we count it as a perfect
		 * prediction
		 */
		new_factor += RESOLUTION;

	/*
	 * We don't want 0 as factor; we always want at least
	 * a tiny bit of estimated time.
	 */
	if (new_factor == 0)
		new_factor = 1;

	data->correction_factor[data->bucket] = new_factor;
}

/**
 * menu_enable_device - scans a CPU's states and does setup
 * @dev: the CPU
 */
static int menu_enable_device(struct cpuidle_device *dev)
{
	struct menu_device *data = &per_cpu(menu_devices, dev->cpu);

	memset(data, 0, sizeof(struct menu_device));

	return 0;
}

static struct cpuidle_governor menu_governor = {
	.name =		"menu",
	.rating =	20,
	.enable =	menu_enable_device,
	.select =	menu_select,
	.reflect =	menu_reflect,
	.owner =	THIS_MODULE,
};

/**
 * init_menu - initializes the governor
 */
static int __init init_menu(void)
{
	return cpuidle_register_governor(&menu_governor);
}

/**
 * exit_menu - exits the governor
 */
static void __exit exit_menu(void)
{
	cpuidle_unregister_governor(&menu_governor);
}

MODULE_LICENSE("GPL");
module_init(init_menu);
module_exit(exit_menu);
Commit	Line	Data
4f86d3a8 LB	1	/*
	2	* menu.c - the menu idle governor
	3	*
	4	* Copyright (C) 2006-2007 Adam Belay <abelay@novell.com>
69d25870 AV	5	* Copyright (C) 2009 Intel Corporation
	6	* Author:
	7	* Arjan van de Ven <arjan@linux.intel.com>
4f86d3a8	8	*
69d25870 AV	9	* This code is licenced under the GPL version 2 as described
69d25870 AV	10	* in the COPYING file that acompanies the Linux Kernel.
4f86d3a8 LB	11	*/
	12
	13	#include <linux/kernel.h>
	14	#include <linux/cpuidle.h>
d82b3518	15	#include <linux/pm_qos_params.h>
4f86d3a8 LB	16	#include <linux/time.h>
	17	#include <linux/ktime.h>
	18	#include <linux/hrtimer.h>
	19	#include <linux/tick.h>
69d25870	20	#include <linux/sched.h>
4f86d3a8	21
69d25870 AV	22	#define BUCKETS 12
	23	#define RESOLUTION 1024
	24	#define DECAY 4
	25	#define MAX_INTERESTING 50000
	26
	27	/*
	28	* Concepts and ideas behind the menu governor
	29	*
	30	* For the menu governor, there are 3 decision factors for picking a C
	31	* state:
	32	* 1) Energy break even point
	33	* 2) Performance impact
	34	* 3) Latency tolerance (from pmqos infrastructure)
	35	* These these three factors are treated independently.
	36	*
	37	* Energy break even point
	38	* -----------------------
	39	* C state entry and exit have an energy cost, and a certain amount of time in
	40	* the C state is required to actually break even on this cost. CPUIDLE
	41	* provides us this duration in the "target_residency" field. So all that we
	42	* need is a good prediction of how long we'll be idle. Like the traditional
	43	* menu governor, we start with the actual known "next timer event" time.
	44	*
	45	* Since there are other source of wakeups (interrupts for example) than
	46	* the next timer event, this estimation is rather optimistic. To get a
	47	* more realistic estimate, a correction factor is applied to the estimate,
	48	* that is based on historic behavior. For example, if in the past the actual
	49	* duration always was 50% of the next timer tick, the correction factor will
	50	* be 0.5.
	51	*
	52	* menu uses a running average for this correction factor, however it uses a
	53	* set of factors, not just a single factor. This stems from the realization
	54	* that the ratio is dependent on the order of magnitude of the expected
	55	* duration; if we expect 500 milliseconds of idle time the likelihood of
	56	* getting an interrupt very early is much higher than if we expect 50 micro
	57	* seconds of idle time. A second independent factor that has big impact on
	58	* the actual factor is if there is (disk) IO outstanding or not.
	59	* (as a special twist, we consider every sleep longer than 50 milliseconds
	60	* as perfect; there are no power gains for sleeping longer than this)
	61	*
	62	* For these two reasons we keep an array of 12 independent factors, that gets
	63	* indexed based on the magnitude of the expected duration as well as the
	64	* "is IO outstanding" property.
	65	*
	66	* Limiting Performance Impact
	67	* ---------------------------
	68	* C states, especially those with large exit latencies, can have a real
	69	* noticable impact on workloads, which is not acceptable for most sysadmins,
	70	* and in addition, less performance has a power price of its own.
	71	*
	72	* As a general rule of thumb, menu assumes that the following heuristic
	73	* holds:
	74	* The busier the system, the less impact of C states is acceptable
	75	*
	76	* This rule-of-thumb is implemented using a performance-multiplier:
	77	* If the exit latency times the performance multiplier is longer than
	78	* the predicted duration, the C state is not considered a candidate
	79	* for selection due to a too high performance impact. So the higher
	80	* this multiplier is, the longer we need to be idle to pick a deep C
	81	* state, and thus the less likely a busy CPU will hit such a deep
	82	* C state.
	83	*
	84	* Two factors are used in determing this multiplier:
	85	* a value of 10 is added for each point of "per cpu load average" we have.
86	* a value of 5 points is added for each process that is waiting for
87	* IO on this CPU.
88	* (these values are experimentally determined)
89	*
90	* The load average factor gives a longer term (few seconds) input to the
91	* decision, while the iowait value gives a cpu local instantanious input.
92	* The iowait factor may look low, but realize that this is also already
93	* represented in the system load average.
94	*
95	*/
4f86d3a8 LB	96
	97	struct menu_device {
	98	int last_state_idx;
672917dc	99	int needs_update;
4f86d3a8 LB	100
4f86d3a8 LB	101	unsigned int expected_us;
69d25870 AV	102	u64 predicted_us;
	103	unsigned int measured_us;
	104	unsigned int exit_us;
	105	unsigned int bucket;
	106	u64 correction_factor[BUCKETS];
4f86d3a8 LB	107	};
4f86d3a8 LB	108
69d25870 AV	109
	110	#define LOAD_INT(x) ((x) >> FSHIFT)
	111	#define LOAD_FRAC(x) LOAD_INT(((x) & (FIXED_1-1)) * 100)
	112
	113	static int get_loadavg(void)
	114	{
	115	unsigned long this = this_cpu_load();
	116
	117
	118	return LOAD_INT(this) * 10 + LOAD_FRAC(this) / 10;
	119	}
	120
	121	static inline int which_bucket(unsigned int duration)
	122	{
	123	int bucket = 0;
	124
	125	/*
	126	* We keep two groups of stats; one with no
	127	* IO pending, one without.
	128	* This allows us to calculate
	129	* E(duration)\|iowait
	130	*/
	131	if (nr_iowait_cpu())
	132	bucket = BUCKETS/2;
	133
	134	if (duration < 10)
	135	return bucket;
	136	if (duration < 100)
	137	return bucket + 1;
	138	if (duration < 1000)
	139	return bucket + 2;
	140	if (duration < 10000)
	141	return bucket + 3;
	142	if (duration < 100000)
	143	return bucket + 4;
	144	return bucket + 5;
	145	}
	146
	147	/*
	148	* Return a multiplier for the exit latency that is intended
	149	* to take performance requirements into account.
	150	* The more performance critical we estimate the system
	151	* to be, the higher this multiplier, and thus the higher
	152	* the barrier to go to an expensive C state.
	153	*/
	154	static inline int performance_multiplier(void)
	155	{
	156	int mult = 1;
	157
	158	/* for higher loadavg, we are more reluctant */
	159
	160	mult += 2 * get_loadavg();
	161
	162	/* for IO wait tasks (per cpu!) we add 5x each */
	163	mult += 10 * nr_iowait_cpu();
	164
	165	return mult;
	166	}
	167
4f86d3a8 LB	168	static DEFINE_PER_CPU(struct menu_device, menu_devices);
4f86d3a8 LB	169
672917dc CZ	170	static void menu_update(struct cpuidle_device *dev);
672917dc CZ	171
4f86d3a8 LB	172	/**
	173	* menu_select - selects the next idle state to enter
	174	* @dev: the CPU
	175	*/
	176	static int menu_select(struct cpuidle_device *dev)
	177	{
	178	struct menu_device *data = &__get_cpu_var(menu_devices);
a2bd9202	179	int latency_req = pm_qos_requirement(PM_QOS_CPU_DMA_LATENCY);
4f86d3a8	180	int i;
69d25870 AV	181	int multiplier;
	182
	183	data->last_state_idx = 0;
	184	data->exit_us = 0;
4f86d3a8	185
672917dc CZ	186	if (data->needs_update) {
	187	menu_update(dev);
	188	data->needs_update = 0;
	189	}
	190
a2bd9202	191	/* Special case when user has set very strict latency requirement */
69d25870	192	if (unlikely(latency_req == 0))
a2bd9202	193	return 0;
a2bd9202	194
69d25870	195	/* determine the expected residency time, round up */
4f86d3a8	196	data->expected_us =
69d25870 AV	197	DIV_ROUND_UP((u32)ktime_to_ns(tick_nohz_get_sleep_length()), 1000);
	198
	199
	200	data->bucket = which_bucket(data->expected_us);
	201
	202	multiplier = performance_multiplier();
	203
	204	/*
	205	* if the correction factor is 0 (eg first time init or cpu hotplug
	206	* etc), we actually want to start out with a unity factor.
	207	*/
	208	if (data->correction_factor[data->bucket] == 0)
	209	data->correction_factor[data->bucket] = RESOLUTION * DECAY;
	210
	211	/* Make sure to round up for half microseconds */
	212	data->predicted_us = DIV_ROUND_CLOSEST(
	213	data->expected_us * data->correction_factor[data->bucket],
	214	RESOLUTION * DECAY);
	215
	216	/*
	217	* We want to default to C1 (hlt), not to busy polling
	218	* unless the timer is happening really really soon.
	219	*/
	220	if (data->expected_us > 5)
	221	data->last_state_idx = CPUIDLE_DRIVER_STATE_START;
4f86d3a8	222
816bb611	223
4f86d3a8	224	/* find the deepest idle state that satisfies our constraints */
69d25870	225	for (i = CPUIDLE_DRIVER_STATE_START; i < dev->state_count; i++) {
4f86d3a8 LB	226	struct cpuidle_state *s = &dev->states[i];
4f86d3a8 LB	227
4f86d3a8 LB	228	if (s->target_residency > data->predicted_us)
4f86d3a8 LB	229	break;
a2bd9202	230	if (s->exit_latency > latency_req)
4f86d3a8	231	break;
69d25870 AV	232	if (s->exit_latency * multiplier > data->predicted_us)
	233	break;
	234	data->exit_us = s->exit_latency;
	235	data->last_state_idx = i;
4f86d3a8 LB	236	}
4f86d3a8 LB	237
69d25870	238	return data->last_state_idx;
4f86d3a8 LB	239	}
	240
	241	/**
672917dc	242	* menu_reflect - records that data structures need update
4f86d3a8 LB	243	* @dev: the CPU
	244	*
	245	* NOTE: it's important to be fast here because this operation will add to
	246	* the overall exit latency.
	247	*/
	248	static void menu_reflect(struct cpuidle_device *dev)
672917dc CZ	249	{
	250	struct menu_device *data = &__get_cpu_var(menu_devices);
	251	data->needs_update = 1;
	252	}
	253
	254	/**
	255	* menu_update - attempts to guess what happened after entry
	256	* @dev: the CPU
	257	*/
	258	static void menu_update(struct cpuidle_device *dev)
4f86d3a8 LB	259	{
	260	struct menu_device *data = &__get_cpu_var(menu_devices);
	261	int last_idx = data->last_state_idx;
320eee77	262	unsigned int last_idle_us = cpuidle_get_last_residency(dev);
4f86d3a8	263	struct cpuidle_state *target = &dev->states[last_idx];
320eee77	264	unsigned int measured_us;
69d25870	265	u64 new_factor;
4f86d3a8 LB	266
	267	/*
	268	* Ugh, this idle state doesn't support residency measurements, so we
	269	* are basically lost in the dark. As a compromise, assume we slept
69d25870	270	* for the whole expected time.
4f86d3a8	271	*/
320eee77	272	if (unlikely(!(target->flags & CPUIDLE_FLAG_TIME_VALID)))
69d25870 AV	273	last_idle_us = data->expected_us;
	274
	275
	276	measured_us = last_idle_us;
4f86d3a8	277
320eee77	278	/*
69d25870 AV	279	* We correct for the exit latency; we are assuming here that the
69d25870 AV	280	* exit latency happens after the event that we're interested in.
320eee77	281	*/
69d25870 AV	282	if (measured_us > data->exit_us)
	283	measured_us -= data->exit_us;
	284
	285
	286	/* update our correction ratio */
	287
	288	new_factor = data->correction_factor[data->bucket]
	289	* (DECAY - 1) / DECAY;
	290
	291	if (data->expected_us > 0 && data->measured_us < MAX_INTERESTING)
	292	new_factor += RESOLUTION * measured_us / data->expected_us;
320eee77	293	else
69d25870 AV	294	/*
	295	* we were idle so long that we count it as a perfect
	296	* prediction
	297	*/
	298	new_factor += RESOLUTION;
320eee77	299
69d25870 AV	300	/*
	301	* We don't want 0 as factor; we always want at least
	302	* a tiny bit of estimated time.
	303	*/
	304	if (new_factor == 0)
	305	new_factor = 1;
320eee77	306
69d25870	307	data->correction_factor[data->bucket] = new_factor;
4f86d3a8 LB	308	}
	309
	310	/**
	311	* menu_enable_device - scans a CPU's states and does setup
	312	* @dev: the CPU
	313	*/
	314	static int menu_enable_device(struct cpuidle_device *dev)
	315	{
	316	struct menu_device *data = &per_cpu(menu_devices, dev->cpu);
	317
	318	memset(data, 0, sizeof(struct menu_device));
	319
	320	return 0;
	321	}
	322
	323	static struct cpuidle_governor menu_governor = {
	324	.name = "menu",
	325	.rating = 20,
	326	.enable = menu_enable_device,
	327	.select = menu_select,
	328	.reflect = menu_reflect,
	329	.owner = THIS_MODULE,
	330	};
	331
	332	/**
	333	* init_menu - initializes the governor
	334	*/
	335	static int __init init_menu(void)
	336	{
	337	return cpuidle_register_governor(&menu_governor);
	338	}
	339
	340	/**
	341	* exit_menu - exits the governor
	342	*/
	343	static void __exit exit_menu(void)
	344	{
	345	cpuidle_unregister_governor(&menu_governor);
	346	}
	347
	348	MODULE_LICENSE("GPL");
	349	module_init(init_menu);
	350	module_exit(exit_menu);