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Diffstat (limited to 'drivers/cpuidle/governors/menu.c')
| -rw-r--r-- | drivers/cpuidle/governors/menu.c | 438 |
1 files changed, 438 insertions, 0 deletions
diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c new file mode 100644 index 00000000..746f1e6b --- /dev/null +++ b/drivers/cpuidle/governors/menu.c @@ -0,0 +1,438 @@ +/* + * 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 + + +/* + * 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 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); +} + +/* + * 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 detect_repeating_patterns(struct menu_device *data) +{ + int i; + uint64_t avg = 0; + uint64_t stddev = 0; /* contains the square of the std deviation */ + + /* first calculate average and standard deviation of the past */ + for (i = 0; i < INTERVALS; i++) + avg += data->intervals[i]; + avg = avg / INTERVALS; + + /* if the avg is beyond the known next tick, it's worthless */ + if (avg > data->expected_us) + return; + + for (i = 0; i < INTERVALS; i++) + stddev += (data->intervals[i] - avg) * + (data->intervals[i] - avg); + + stddev = stddev / INTERVALS; + + /* + * now.. if stddev is small.. then assume we have a + * repeating pattern and predict we keep doing this. + */ + + if (avg && stddev < STDDEV_THRESH) + data->predicted_us = avg; +} + +/** + * 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 power_usage = -1; + int i; + int multiplier; + struct timespec t; + + 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); + + detect_repeating_patterns(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].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]; + + if (s->disable) + continue; + if (s->target_residency > data->predicted_us) + continue; + if (s->exit_latency > latency_req) + continue; + if (s->exit_latency * multiplier > data->predicted_us) + continue; + + if (s->power_usage < power_usage) { + power_usage = s->power_usage; + data->last_state_idx = i; + data->exit_us = s->exit_latency; + } + } + + 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); + + 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); |