816bb611e4
Add decaying history of predicted idle time, instead of using the last early wakeup. This logic helps menu governor do better job of predicting idle time. With this change, we also measured noticable (~8%) power savings on a DP server system with CPUs supporting deep C states, when system was lightly loaded. There was no change to power or perf on other load conditions. Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com> Signed-off-by: Len Brown <len.brown@intel.com>
160 lines
4.0 KiB
C
160 lines
4.0 KiB
C
/*
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* menu.c - the menu idle governor
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*
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* Copyright (C) 2006-2007 Adam Belay <abelay@novell.com>
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*
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* This code is licenced under the GPL.
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*/
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#include <linux/kernel.h>
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#include <linux/cpuidle.h>
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#include <linux/pm_qos_params.h>
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#include <linux/time.h>
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#include <linux/ktime.h>
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#include <linux/hrtimer.h>
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#include <linux/tick.h>
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#define BREAK_FUZZ 4 /* 4 us */
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#define PRED_HISTORY_PCT 50
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struct menu_device {
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int last_state_idx;
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unsigned int expected_us;
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unsigned int predicted_us;
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unsigned int current_predicted_us;
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unsigned int last_measured_us;
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unsigned int elapsed_us;
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};
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static DEFINE_PER_CPU(struct menu_device, menu_devices);
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/**
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* menu_select - selects the next idle state to enter
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* @dev: the CPU
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*/
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static int menu_select(struct cpuidle_device *dev)
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{
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struct menu_device *data = &__get_cpu_var(menu_devices);
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int latency_req = pm_qos_requirement(PM_QOS_CPU_DMA_LATENCY);
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int i;
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/* Special case when user has set very strict latency requirement */
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if (unlikely(latency_req == 0)) {
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data->last_state_idx = 0;
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return 0;
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}
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/* determine the expected residency time */
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data->expected_us =
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(u32) ktime_to_ns(tick_nohz_get_sleep_length()) / 1000;
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/* Recalculate predicted_us based on prediction_history_pct */
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data->predicted_us *= PRED_HISTORY_PCT;
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data->predicted_us += (100 - PRED_HISTORY_PCT) *
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data->current_predicted_us;
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data->predicted_us /= 100;
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/* find the deepest idle state that satisfies our constraints */
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for (i = CPUIDLE_DRIVER_STATE_START + 1; i < dev->state_count; i++) {
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struct cpuidle_state *s = &dev->states[i];
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if (s->target_residency > data->expected_us)
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break;
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if (s->target_residency > data->predicted_us)
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break;
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if (s->exit_latency > latency_req)
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break;
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}
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data->last_state_idx = i - 1;
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return i - 1;
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}
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/**
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* menu_reflect - attempts to guess what happened after entry
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* @dev: the CPU
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*
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* NOTE: it's important to be fast here because this operation will add to
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* the overall exit latency.
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*/
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static void menu_reflect(struct cpuidle_device *dev)
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{
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struct menu_device *data = &__get_cpu_var(menu_devices);
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int last_idx = data->last_state_idx;
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unsigned int last_idle_us = cpuidle_get_last_residency(dev);
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struct cpuidle_state *target = &dev->states[last_idx];
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unsigned int measured_us;
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/*
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* Ugh, this idle state doesn't support residency measurements, so we
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* are basically lost in the dark. As a compromise, assume we slept
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* for one full standard timer tick. However, be aware that this
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* could potentially result in a suboptimal state transition.
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*/
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if (unlikely(!(target->flags & CPUIDLE_FLAG_TIME_VALID)))
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last_idle_us = USEC_PER_SEC / HZ;
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/*
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* measured_us and elapsed_us are the cumulative idle time, since the
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* last time we were woken out of idle by an interrupt.
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*/
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if (data->elapsed_us <= data->elapsed_us + last_idle_us)
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measured_us = data->elapsed_us + last_idle_us;
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else
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measured_us = -1;
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/* Predict time until next break event */
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data->current_predicted_us = max(measured_us, data->last_measured_us);
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if (last_idle_us + BREAK_FUZZ <
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data->expected_us - target->exit_latency) {
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data->last_measured_us = measured_us;
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data->elapsed_us = 0;
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} else {
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data->elapsed_us = measured_us;
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}
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}
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/**
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* menu_enable_device - scans a CPU's states and does setup
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* @dev: the CPU
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*/
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static int menu_enable_device(struct cpuidle_device *dev)
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{
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struct menu_device *data = &per_cpu(menu_devices, dev->cpu);
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memset(data, 0, sizeof(struct menu_device));
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return 0;
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}
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static struct cpuidle_governor menu_governor = {
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.name = "menu",
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.rating = 20,
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.enable = menu_enable_device,
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.select = menu_select,
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.reflect = menu_reflect,
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.owner = THIS_MODULE,
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};
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/**
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* init_menu - initializes the governor
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*/
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static int __init init_menu(void)
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{
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return cpuidle_register_governor(&menu_governor);
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}
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/**
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* exit_menu - exits the governor
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*/
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static void __exit exit_menu(void)
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{
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cpuidle_unregister_governor(&menu_governor);
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}
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MODULE_LICENSE("GPL");
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module_init(init_menu);
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module_exit(exit_menu);
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