drivers/cpuidle/governors/menu.c - kernel/prism - Git at Google

 /*
  * 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>
 #include <linux/math64.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);

 /* This implements DIV_ROUND_CLOSEST but avoids 64 bit division */
 static u64 div_round64(u64 dividend, u32 divisor)
 {
 	return div_u64(dividend + (divisor / 2), divisor);
 }

 /**
  * 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_round64(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);
	/*
	* 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>
	#include <linux/math64.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);

	/* This implements DIV_ROUND_CLOSEST but avoids 64 bit division */
	static u64 div_round64(u64 dividend, u32 divisor)
	{
	return div_u64(dividend + (divisor / 2), divisor);
	}

	/**
	* 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_round64(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);