--- /dev/null
+/*
+ * 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>
+
+/*
+ * Please note when changing the tuning values:
+ * If (MAX_INTERESTING-1) * RESOLUTION > UINT_MAX, the result of
+ * a scaling operation multiplication may overflow on 32 bit platforms.
+ * In that case, #define RESOLUTION as ULL to get 64 bit result:
+ * #define RESOLUTION 1024ULL
+ *
+ * The default values do not overflow.
+ */
+#define BUCKETS 12
+#define INTERVAL_SHIFT 3
+#define INTERVALS (1UL << INTERVAL_SHIFT)
+#define RESOLUTION 1024
+#define DECAY 8
+#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.
+ *
+ * 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.
+ *
+ */
+
+struct menu_device {
+ int last_state_idx;
+ int needs_update;
+
+ unsigned int next_timer_us;
+ unsigned int predicted_us;
+ unsigned int bucket;
+ unsigned int correction_factor[BUCKETS];
+ unsigned int intervals[INTERVALS];
+ int interval_ptr;
+};
+
+
+#define LOAD_INT(x) ((x) >> FSHIFT)
+#define LOAD_FRAC(x) LOAD_INT(((x) & (FIXED_1-1)) * 100)
+
+static inline int get_loadavg(unsigned long load)
+{
+ return LOAD_INT(load) * 10 + LOAD_FRAC(load) / 10;
+}
+
+static inline int which_bucket(unsigned int duration, unsigned long nr_iowaiters)
+{
+ 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_iowaiters)
+ 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(unsigned long nr_iowaiters, unsigned long load)
+{
+ int mult = 1;
+
+ /* for higher loadavg, we are more reluctant */
+
+ mult += 2 * get_loadavg(load);
+
+ /* for IO wait tasks (per cpu!) we add 5x each */
+ mult += 10 * nr_iowaiters;
+
+ return mult;
+}
+
+static DEFINE_PER_CPU(struct menu_device, menu_devices);
+
+static void menu_update(struct cpuidle_driver *drv, struct cpuidle_device *dev);
+
+/*
+ * 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 void get_typical_interval(struct menu_device *data)
+{
+ int i, divisor;
+ unsigned int max, thresh;
+ uint64_t avg, stddev;
+
+ thresh = UINT_MAX; /* Discard outliers above this value */
+
+again:
+
+ /* First calculate the average of past intervals */
+ max = 0;
+ avg = 0;
+ divisor = 0;
+ for (i = 0; i < INTERVALS; i++) {
+ unsigned int value = data->intervals[i];
+ if (value <= thresh) {
+ avg += value;
+ divisor++;
+ if (value > max)
+ max = value;
+ }
+ }
+ if (divisor == INTERVALS)
+ avg >>= INTERVAL_SHIFT;
+ else
+ do_div(avg, divisor);
+
+ /* Then try to determine standard deviation */
+ stddev = 0;
+ for (i = 0; i < INTERVALS; i++) {
+ unsigned int value = data->intervals[i];
+ if (value <= thresh) {
+ int64_t diff = value - avg;
+ stddev += diff * diff;
+ }
+ }
+ if (divisor == INTERVALS)
+ stddev >>= INTERVAL_SHIFT;
+ else
+ do_div(stddev, divisor);
+
+ /*
+ * The typical interval is obtained when standard deviation is small
+ * or standard deviation is small compared to the average interval.
+ *
+ * int_sqrt() formal parameter type is unsigned long. When the
+ * greatest difference to an outlier exceeds ~65 ms * sqrt(divisor)
+ * the resulting squared standard deviation exceeds the input domain
+ * of int_sqrt on platforms where unsigned long is 32 bits in size.
+ * In such case reject the candidate average.
+ *
+ * Use this result only if there is no timer to wake us up sooner.
+ */
+ if (likely(stddev <= ULONG_MAX)) {
+ stddev = int_sqrt(stddev);
+ if (((avg > stddev * 6) && (divisor * 4 >= INTERVALS * 3))
+ || stddev <= 20) {
+ if (data->next_timer_us > avg)
+ data->predicted_us = avg;
+ return;
+ }
+ }
+
+ /*
+ * 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.
+ */
+ if ((divisor * 4) <= INTERVALS * 3)
+ return;
+
+ thresh = max - 1;
+ goto again;
+}
+
+/**
+ * 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 = this_cpu_ptr(&menu_devices);
+ int latency_req = pm_qos_request(PM_QOS_CPU_DMA_LATENCY);
+ int i;
+ unsigned int interactivity_req;
+ unsigned long nr_iowaiters, cpu_load;
+
+ if (data->needs_update) {
+ menu_update(drv, dev);
+ data->needs_update = 0;
+ }
+
+ data->last_state_idx = CPUIDLE_DRIVER_STATE_START - 1;
+
+ /* 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->next_timer_us = ktime_to_us(tick_nohz_get_sleep_length());
+
+ get_iowait_load(&nr_iowaiters, &cpu_load);
+ data->bucket = which_bucket(data->next_timer_us, nr_iowaiters);
+
+ /*
+ * Force the result of multiplication to be 64 bits even if both
+ * operands are 32 bits.
+ * Make sure to round up for half microseconds.
+ */
+ data->predicted_us = DIV_ROUND_CLOSEST_ULL((uint64_t)data->next_timer_us *
+ data->correction_factor[data->bucket],
+ RESOLUTION * DECAY);
+
+ get_typical_interval(data);
+
+ /*
+ * Performance multiplier defines a minimum predicted idle
+ * duration / latency ratio. Adjust the latency limit if
+ * necessary.
+ */
+ interactivity_req = data->predicted_us / performance_multiplier(nr_iowaiters, cpu_load);
+ if (latency_req > interactivity_req)
+ latency_req = interactivity_req;
+
+ /*
+ * We want to default to C1 (hlt), not to busy polling
+ * unless the timer is happening really really soon.
+ */
+ if (data->next_timer_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)
+ continue;
+ if (s->exit_latency > latency_req)
+ continue;
+
+ data->last_state_idx = i;
+ }
+
+ 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 = this_cpu_ptr(&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 = this_cpu_ptr(&menu_devices);
+ int last_idx = data->last_state_idx;
+ struct cpuidle_state *target = &drv->states[last_idx];
+ unsigned int measured_us;
+ unsigned int new_factor;
+
+ /*
+ * Try to figure out how much time passed between entry to low
+ * power state and occurrence of the wakeup event.
+ *
+ * If the entered idle state didn't support residency measurements,
+ * we use them anyway if they are short, and if long,
+ * truncate to the whole expected time.
+ *
+ * Any measured amount of time will include the exit latency.
+ * Since we are interested in when the wakeup begun, not when it
+ * was completed, we must subtract the exit latency. However, if
+ * the measured amount of time is less than the exit latency,
+ * assume the state was never reached and the exit latency is 0.
+ */
+
+ /* measured value */
+ measured_us = cpuidle_get_last_residency(dev);
+
+ /* Deduct exit latency */
+ if (measured_us > target->exit_latency)
+ measured_us -= target->exit_latency;
+
+ /* Make sure our coefficients do not exceed unity */
+ if (measured_us > data->next_timer_us)
+ measured_us = data->next_timer_us;
+
+ /* Update our correction ratio */
+ new_factor = data->correction_factor[data->bucket];
+ new_factor -= new_factor / DECAY;
+
+ if (data->next_timer_us > 0 && measured_us < MAX_INTERESTING)
+ new_factor += RESOLUTION * measured_us / data->next_timer_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. Fortunately, due to rounding,
+ * new_factor will stay nonzero regardless of measured_us values
+ * and the compiler can eliminate this test as long as DECAY > 1.
+ */
+ if (DECAY == 1 && unlikely(new_factor == 0))
+ new_factor = 1;
+
+ data->correction_factor[data->bucket] = new_factor;
+
+ /* update the repeating-pattern data */
+ data->intervals[data->interval_ptr++] = measured_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);
+ int i;
+
+ memset(data, 0, sizeof(struct menu_device));
+
+ /*
+ * if the correction factor is 0 (eg first time init or cpu hotplug
+ * etc), we actually want to start out with a unity factor.
+ */
+ for(i = 0; i < BUCKETS; i++)
+ data->correction_factor[i] = RESOLUTION * DECAY;
+
+ 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);
+}
+
+postcore_initcall(init_menu);
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