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![Ramesh Thomas](/assets/img/avatar_default.png)
Individual CPUs may have special requirements to not enter deep idle states. For example, a CPU running real time applications would not want to enter deep idle states to avoid latency impacts. At the same time other CPUs that do not have such a requirement could allow deep idle states to save power. This was already implemented in the menu governor. Implementing similar changes in the ladder governor which gets selected when CONFIG_NO_HZ and CONFIG_NO_HZ_IDLE are not set. Refer following commits for the menu governor changes. Signed-off-by: Ramesh Thomas <ramesh.thomas@intel.com> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
206 lines
5.5 KiB
C
206 lines
5.5 KiB
C
/*
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* ladder.c - the residency ladder algorithm
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*
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* Copyright (C) 2001, 2002 Andy Grover <andrew.grover@intel.com>
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* Copyright (C) 2001, 2002 Paul Diefenbaugh <paul.s.diefenbaugh@intel.com>
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* Copyright (C) 2004, 2005 Dominik Brodowski <linux@brodo.de>
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*
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* (C) 2006-2007 Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
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* Shaohua Li <shaohua.li@intel.com>
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* 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.h>
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#include <linux/jiffies.h>
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#include <linux/tick.h>
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#include <linux/cpu.h>
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#include <asm/io.h>
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#include <linux/uaccess.h>
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#define PROMOTION_COUNT 4
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#define DEMOTION_COUNT 1
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struct ladder_device_state {
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struct {
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u32 promotion_count;
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u32 demotion_count;
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u32 promotion_time;
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u32 demotion_time;
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} threshold;
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struct {
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int promotion_count;
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int demotion_count;
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} stats;
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};
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struct ladder_device {
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struct ladder_device_state states[CPUIDLE_STATE_MAX];
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int last_state_idx;
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};
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static DEFINE_PER_CPU(struct ladder_device, ladder_devices);
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/**
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* ladder_do_selection - prepares private data for a state change
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* @ldev: the ladder device
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* @old_idx: the current state index
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* @new_idx: the new target state index
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*/
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static inline void ladder_do_selection(struct ladder_device *ldev,
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int old_idx, int new_idx)
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{
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ldev->states[old_idx].stats.promotion_count = 0;
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ldev->states[old_idx].stats.demotion_count = 0;
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ldev->last_state_idx = new_idx;
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}
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/**
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* ladder_select_state - selects the next state to enter
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* @drv: cpuidle driver
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* @dev: the CPU
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*/
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static int ladder_select_state(struct cpuidle_driver *drv,
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struct cpuidle_device *dev)
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{
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struct ladder_device *ldev = this_cpu_ptr(&ladder_devices);
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struct device *device = get_cpu_device(dev->cpu);
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struct ladder_device_state *last_state;
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int last_residency, last_idx = ldev->last_state_idx;
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int first_idx = drv->states[0].flags & CPUIDLE_FLAG_POLLING ? 1 : 0;
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int latency_req = pm_qos_request(PM_QOS_CPU_DMA_LATENCY);
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int resume_latency = dev_pm_qos_raw_read_value(device);
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if (resume_latency < latency_req &&
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resume_latency != PM_QOS_RESUME_LATENCY_NO_CONSTRAINT)
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latency_req = resume_latency;
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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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ladder_do_selection(ldev, last_idx, 0);
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return 0;
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}
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last_state = &ldev->states[last_idx];
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last_residency = cpuidle_get_last_residency(dev) - drv->states[last_idx].exit_latency;
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/* consider promotion */
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if (last_idx < drv->state_count - 1 &&
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!drv->states[last_idx + 1].disabled &&
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!dev->states_usage[last_idx + 1].disable &&
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last_residency > last_state->threshold.promotion_time &&
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drv->states[last_idx + 1].exit_latency <= latency_req) {
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last_state->stats.promotion_count++;
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last_state->stats.demotion_count = 0;
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if (last_state->stats.promotion_count >= last_state->threshold.promotion_count) {
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ladder_do_selection(ldev, last_idx, last_idx + 1);
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return last_idx + 1;
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}
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}
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/* consider demotion */
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if (last_idx > first_idx &&
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(drv->states[last_idx].disabled ||
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dev->states_usage[last_idx].disable ||
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drv->states[last_idx].exit_latency > latency_req)) {
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int i;
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for (i = last_idx - 1; i > first_idx; i--) {
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if (drv->states[i].exit_latency <= latency_req)
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break;
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}
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ladder_do_selection(ldev, last_idx, i);
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return i;
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}
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if (last_idx > first_idx &&
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last_residency < last_state->threshold.demotion_time) {
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last_state->stats.demotion_count++;
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last_state->stats.promotion_count = 0;
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if (last_state->stats.demotion_count >= last_state->threshold.demotion_count) {
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ladder_do_selection(ldev, last_idx, last_idx - 1);
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return last_idx - 1;
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}
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}
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/* otherwise remain at the current state */
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return last_idx;
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}
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/**
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* ladder_enable_device - setup for the governor
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* @drv: cpuidle driver
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* @dev: the CPU
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*/
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static int ladder_enable_device(struct cpuidle_driver *drv,
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struct cpuidle_device *dev)
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{
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int i;
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int first_idx = drv->states[0].flags & CPUIDLE_FLAG_POLLING ? 1 : 0;
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struct ladder_device *ldev = &per_cpu(ladder_devices, dev->cpu);
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struct ladder_device_state *lstate;
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struct cpuidle_state *state;
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ldev->last_state_idx = first_idx;
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for (i = first_idx; i < drv->state_count; i++) {
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state = &drv->states[i];
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lstate = &ldev->states[i];
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lstate->stats.promotion_count = 0;
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lstate->stats.demotion_count = 0;
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lstate->threshold.promotion_count = PROMOTION_COUNT;
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lstate->threshold.demotion_count = DEMOTION_COUNT;
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if (i < drv->state_count - 1)
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lstate->threshold.promotion_time = state->exit_latency;
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if (i > first_idx)
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lstate->threshold.demotion_time = state->exit_latency;
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}
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return 0;
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}
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/**
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* ladder_reflect - update the correct last_state_idx
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* @dev: the CPU
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* @index: the index of actual state entered
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*/
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static void ladder_reflect(struct cpuidle_device *dev, int index)
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{
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struct ladder_device *ldev = this_cpu_ptr(&ladder_devices);
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if (index > 0)
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ldev->last_state_idx = index;
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}
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static struct cpuidle_governor ladder_governor = {
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.name = "ladder",
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.rating = 10,
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.enable = ladder_enable_device,
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.select = ladder_select_state,
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.reflect = ladder_reflect,
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};
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/**
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* init_ladder - initializes the governor
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*/
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static int __init init_ladder(void)
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{
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/*
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* When NO_HZ is disabled, or when booting with nohz=off, the ladder
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* governor is better so give it a higher rating than the menu
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* governor.
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*/
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if (!tick_nohz_enabled)
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ladder_governor.rating = 25;
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return cpuidle_register_governor(&ladder_governor);
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}
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postcore_initcall(init_ladder);
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