diff options
Diffstat (limited to 'drivers/cpuidle/governors/menu.c')
| -rw-r--r-- | drivers/cpuidle/governors/menu.c | 251 |
1 files changed, 212 insertions, 39 deletions
diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c index f1df59f..9f3d775 100644 --- a/drivers/cpuidle/governors/menu.c +++ b/drivers/cpuidle/governors/menu.c @@ -2,8 +2,12 @@ * 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. + * This code is licenced under the GPL version 2 as described + * in the COPYING file that acompanies the Linux Kernel. */ #include <linux/kernel.h> @@ -13,20 +17,153 @@ #include <linux/ktime.h> #include <linux/hrtimer.h> #include <linux/tick.h> +#include <linux/sched.h> -#define BREAK_FUZZ 4 /* 4 us */ -#define PRED_HISTORY_PCT 50 +#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; unsigned int expected_us; - unsigned int predicted_us; - unsigned int current_predicted_us; - unsigned int last_measured_us; - unsigned int elapsed_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); /** @@ -38,37 +175,59 @@ 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; /* Special case when user has set very strict latency requirement */ - if (unlikely(latency_req == 0)) { - data->last_state_idx = 0; + if (unlikely(latency_req == 0)) return 0; - } - /* determine the expected residency time */ + /* determine the expected residency time, round up */ data->expected_us = - (u32) ktime_to_ns(tick_nohz_get_sleep_length()) / 1000; + 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_ROUND_CLOSEST( + 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; - /* Recalculate predicted_us based on prediction_history_pct */ - data->predicted_us *= PRED_HISTORY_PCT; - data->predicted_us += (100 - PRED_HISTORY_PCT) * - data->current_predicted_us; - data->predicted_us /= 100; /* find the deepest idle state that satisfies our constraints */ - for (i = CPUIDLE_DRIVER_STATE_START + 1; i < dev->state_count; i++) { + for (i = CPUIDLE_DRIVER_STATE_START; i < dev->state_count; i++) { struct cpuidle_state *s = &dev->states[i]; - if (s->target_residency > data->expected_us) - break; 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; } - data->last_state_idx = i - 1; - return i - 1; + return data->last_state_idx; } /** @@ -85,35 +244,49 @@ static void menu_reflect(struct cpuidle_device *dev) 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 one full standard timer tick. However, be aware that this - * could potentially result in a suboptimal state transition. + * for the whole expected time. */ if (unlikely(!(target->flags & CPUIDLE_FLAG_TIME_VALID))) - last_idle_us = USEC_PER_SEC / HZ; + last_idle_us = data->expected_us; + + + measured_us = last_idle_us; /* - * measured_us and elapsed_us are the cumulative idle time, since the - * last time we were woken out of idle by an interrupt. + * We correct for the exit latency; we are assuming here that the + * exit latency happens after the event that we're interested in. */ - if (data->elapsed_us <= data->elapsed_us + last_idle_us) - measured_us = data->elapsed_us + last_idle_us; + 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 - measured_us = -1; + /* + * we were idle so long that we count it as a perfect + * prediction + */ + new_factor += RESOLUTION; - /* Predict time until next break event */ - data->current_predicted_us = max(measured_us, data->last_measured_us); + /* + * 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; - if (last_idle_us + BREAK_FUZZ < - data->expected_us - target->exit_latency) { - data->last_measured_us = measured_us; - data->elapsed_us = 0; - } else { - data->elapsed_us = measured_us; - } + data->correction_factor[data->bucket] = new_factor; } /** |