| /* |
| * 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_params.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> |
| |
| #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; |
| int needs_update; |
| |
| unsigned int expected_us; |
| unsigned int measured_us; |
| u64 predicted_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); |
| |
| static void menu_update(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); |
| } |
| |
| /** |
| * menu_select - selects the next idle state to enter |
| * @dev: the CPU |
| */ |
| 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; |
| |
| if (data->needs_update) { |
| menu_update(dev); |
| data->needs_update = 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 */ |
| data->expected_us = |
| 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_round64(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; |
| |
| |
| /* find the deepest idle state that satisfies our constraints */ |
| for (i = CPUIDLE_DRIVER_STATE_START; i < dev->state_count; i++) { |
| struct cpuidle_state *s = &dev->states[i]; |
| |
| 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; |
| } |
| |
| return data->last_state_idx; |
| } |
| |
| /** |
| * menu_reflect - records that data structures need update |
| * @dev: the CPU |
| * |
| * 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) |
| { |
| struct menu_device *data = &__get_cpu_var(menu_devices); |
| data->needs_update = 1; |
| } |
| |
| /** |
| * menu_update - attempts to guess what happened after entry |
| * @dev: the CPU |
| */ |
| static void menu_update(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 = &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 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 && data->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; |
| } |
| |
| /** |
| * menu_enable_device - scans a CPU's states and does setup |
| * @dev: the CPU |
| */ |
| static int menu_enable_device(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); |