/*
* 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.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>
#include <linux/module.h>
#define BUCKETS 12
#define INTERVALS 8
#define RESOLUTION 1024
#define DECAY 8
#define MAX_INTERESTING 50000
#define STDDEV_THRESH 400
/* 60 * 60 > STDDEV_THRESH * INTERVALS = 400 * 8 */
#define MAX_DEVIATION 60
static DEFINE_PER_CPU(struct hrtimer, menu_hrtimer);
static DEFINE_PER_CPU(int, hrtimer_status);
/* menu hrtimer mode */
enum {MENU_HRTIMER_STOP, MENU_HRTIMER_REPEAT, MENU_HRTIMER_GENERAL};
/*
* 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.
*
* Repeatable-interval-detector
* ----------------------------
* There are some cases where "next timer" is a completely unusable predictor:
* Those cases where the interval is fixed, for example due to hardware
* interrupt mitigation, but also due to fixed transfer rate devices such as
* mice.
* For this, we use a different predictor: We track the duration of the last 8
* intervals and if the stand deviation of these 8 intervals is below a
* threshold value, we use the average of these intervals as prediction.
*
* Limiting Performance Impact
* ---------------------------
* C states, especially those with large exit latencies, can have a real
* noticeable 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.
*
*/
/*
* The C-state residency is so long that is is worthwhile to exit
* from the shallow C-state and re-enter into a deeper C-state.
*/
static unsigned int perfect_cstate_ms __read_mostly = 30;
module_param(perfect_cstate_ms, uint, 0000);
struct menu_device {
int last_state_idx;
int needs_update;
unsigned int expected_us;
u64 predicted_us;
unsigned int exit_us;
unsigned int bucket;
u64 correction_factor[BUCKETS];
u32 intervals[INTERVALS];
int interval_ptr;
};
#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(smp_processor_id()))
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 */
/*
* this doesn't work as intended - it is almost always 0, but can
* sometimes, depending on workload, spike very high into the hundreds
* even when the average cpu load is under 10%.
*/
/* mult += 2 * get_loadavg(); */
/* for IO wait tasks (per cpu!) we add 5x each */
mult += 10 * nr_iowait_cpu(smp_processor_id());
return mult;
}
static DEFINE_PER_CPU(struct menu_device, menu_devices);
static void menu_update(struct cpuidle_driver *drv, 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);
}
/* Cancel the hrtimer if it is not triggered yet */
void menu_hrtimer_cancel(void)
{
int cpu = smp_processor_id();
struct hrtimer *hrtmr = &per_cpu(menu_hrtimer, cpu);
/* The timer is still not time out*/
if (per_cpu(hrtimer_status, cpu)) {
hrtimer_cancel(hrtmr);
per_cpu(hrtimer_status, cpu) = MENU_HRTIMER_STOP;
}
}
EXPORT_SYMBOL_GPL(menu_hrtimer_cancel);
/* Call back for hrtimer is triggered */
static enum hrtimer_restart menu_hrtimer_notify(struct hrtimer *hrtimer)
{
int cpu = smp_processor_id();
struct menu_device *data = &per_cpu(menu_devices, cpu);
/* In general case, the expected residency is much larger than
* deepest C-state target residency, but prediction logic still
* predicts a small predicted residency, so the prediction
* history is totally broken if the timer is triggered.
* So reset the correction factor.
*/
if (per_cpu(hrtimer_status, cpu) == MENU_HRTIMER_GENERAL)
data->correction_factor[data->bucket] = RESOLUTION * DECAY;
per_cpu(hrtimer_status, cpu) = MENU_HRTIMER_STOP;
return HRTIMER_NORESTART;
}
/*
* Try detecting repeating patterns by keeping track of the last 8
* intervals, and checking if the standard deviation of that set
* of points is below a threshold. If it is... then use the
* average of these 8 points as the estimated value.
*/
static u32 get_typical_interval(struct menu_device *data)
{
int i = 0, divisor = 0;
uint64_t max = 0, avg = 0, stddev = 0;
int64_t thresh = LLONG_MAX; /* Discard outliers above this value. */
unsigned int ret = 0;
again:
/* first calculate average and standard deviation of the past */
max = avg = divisor = stddev = 0;
for (i = 0; i < INTERVALS; i++) {
int64_t value = data->intervals[i];
if (value <= thresh) {
avg += value;
divisor++;
if (value > max)
max = value;
}
}
do_div(avg, divisor);
for (i = 0; i < INTERVALS; i++) {
int64_t value = data->intervals[i];
if (value <= thresh) {
int64_t diff = value - avg;
stddev += diff * diff;
}
}
do_div(stddev, divisor);
stddev = int_sqrt(stddev);
/*
* If we have outliers to the upside in our distribution, discard
* those by setting the threshold to exclude these outliers, then
* calculate the average and standard deviation again. Once we get
* down to the bottom 3/4 of our samples, stop excluding samples.
*
* This can deal with workloads that have long pauses interspersed
* with sporadic activity with a bunch of short pauses.
*
* The typical interval is obtained when standard deviation is small
* or standard deviation is small compared to the average interval.
*/
if (((avg > stddev * 6) && (divisor * 4 >= INTERVALS * 3))
|| stddev <= 20) {
data->predicted_us = avg;
ret = 1;
return ret;
} else if ((divisor * 4) > INTERVALS * 3) {
/* Exclude the max interval */
thresh = max - 1;
goto again;
}
return ret;
}
/**
* menu_select - selects the next idle state to enter
* @drv: cpuidle driver containing state data
* @dev: the CPU
*/
static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev)
{
struct menu_device *data = &__get_cpu_var(menu_devices);
int latency_req = pm_qos_request(PM_QOS_CPU_DMA_LATENCY);
int i;
int multiplier;
struct timespec t;
int repeat = 0, low_predicted = 0;
int cpu = smp_processor_id();
struct hrtimer *hrtmr = &per_cpu(menu_hrtimer, cpu);
if (data->needs_update) {
menu_update(drv, dev);
data->needs_update = 0;
}
data->last_state_idx = 0;
data->exit_us = 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 */
t = ktime_to_timespec(tick_nohz_get_sleep_length());
data->expected_us =
t.tv_sec * USEC_PER_SEC + t.tv_nsec / NSEC_PER_USEC;
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);
repeat = get_typical_interval(data);
/*
* We want to default to C1 (hlt), not to busy polling
* unless the timer is happening really really soon.
*/
if (data->expected_us > 5 &&
!drv->states[CPUIDLE_DRIVER_STATE_START].disabled &&
dev->states_usage[CPUIDLE_DRIVER_STATE_START].disable == 0)
data->last_state_idx = CPUIDLE_DRIVER_STATE_START;
/*
* Find the idle state with the lowest power while satisfying
* our constraints.
*/
for (i = CPUIDLE_DRIVER_STATE_START; i < drv->state_count; i++) {
struct cpuidle_state *s = &drv->states[i];
struct cpuidle_state_usage *su = &dev->states_usage[i];
if (s->disabled || su->disable)
continue;
if (s->target_residency > data->predicted_us) {
low_predicted = 1;
continue;
}
if (s->exit_latency > latency_req)
continue;
if (s->exit_latency * multiplier > data->predicted_us)
continue;
data->last_state_idx = i;
data->exit_us = s->exit_latency;
}
/* not deepest C-state chosen for low predicted residency */
if (low_predicted) {
unsigned int timer_us = 0;
unsigned int perfect_us = 0;
/*
* Set a timer to detect whether this sleep is much
* longer than repeat mode predicted. If the timer
* triggers, the code will evaluate whether to put
* the CPU into a deeper C-state.
* The timer is cancelled on CPU wakeup.
*/
timer_us = 2 * (data->predicted_us + MAX_DEVIATION);
perfect_us = perfect_cstate_ms * 1000;
if (repeat && (4 * timer_us < data->expected_us)) {
RCU_NONIDLE(hrtimer_start(hrtmr,
ns_to_ktime(1000 * timer_us),
HRTIMER_MODE_REL_PINNED));
/* In repeat case, menu hrtimer is started */
per_cpu(hrtimer_status, cpu) = MENU_HRTIMER_REPEAT;
} else if (perfect_us < data->expected_us) {
/*
* The next timer is long. This could be because
* we did not make a useful prediction.
* In that case, it makes sense to re-enter
* into a deeper C-state after some time.
*/
RCU_NONIDLE(hrtimer_start(hrtmr,
ns_to_ktime(1000 * timer_us),
HRTIMER_MODE_REL_PINNED));
/* In general case, menu hrtimer is started */
per_cpu(hrtimer_status, cpu) = MENU_HRTIMER_GENERAL;
}
}
return data->last_state_idx;
}
/**
* menu_reflect - records that data structures need update
* @dev: the CPU
* @index: the index of actual entered state
*
* 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, int index)
{
struct menu_device *data = &__get_cpu_var(menu_devices);
data->last_state_idx = index;
if (index >= 0)
data->needs_update = 1;
}
/**
* menu_update - attempts to guess what happened after entry
* @drv: cpuidle driver containing state data
* @dev: the CPU
*/
static void menu_update(struct cpuidle_driver *drv, 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 = &drv->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 && 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;
/* update the repeating-pattern data */
data->intervals[data->interval_ptr++] = last_idle_us;
if (data->interval_ptr >= INTERVALS)
data->interval_ptr = 0;
}
/**
* menu_enable_device - scans a CPU's states and does setup
* @drv: cpuidle driver
* @dev: the CPU
*/
static int menu_enable_device(struct cpuidle_driver *drv,
struct cpuidle_device *dev)
{
struct menu_device *data = &per_cpu(menu_devices, dev->cpu);
struct hrtimer *t = &per_cpu(menu_hrtimer, dev->cpu);
hrtimer_init(t, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
t->function = menu_hrtimer_notify;
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);