| /* |
| * 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 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, 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) |
| { |
| 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_iowaiters; |
| |
| 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); |
| } |
| |
| /* |
| * 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 = &__get_cpu_var(menu_devices); |
| int latency_req = pm_qos_request(PM_QOS_CPU_DMA_LATENCY); |
| int i; |
| unsigned int interactivity_req; |
| unsigned long nr_iowaiters; |
| |
| 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()); |
| |
| nr_iowaiters = nr_iowait_cpu(smp_processor_id()); |
| 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_round64((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); |
| 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 = &__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; |
| 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 are basically lost in the dark how much time passed. |
| * As a compromise, assume we slept for 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 substract 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. |
| */ |
| if (unlikely(!(target->flags & CPUIDLE_FLAG_TIME_VALID))) { |
| /* Use timer value as is */ |
| measured_us = data->next_timer_us; |
| |
| } else { |
| /* Use 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); |