1/*
2 * ladder.c - the residency ladder algorithm
3 *
4 * Copyright (C) 2001, 2002 Andy Grover <andrew.grover@intel.com>
5 * Copyright (C) 2001, 2002 Paul Diefenbaugh <paul.s.diefenbaugh@intel.com>
6 * Copyright (C) 2004, 2005 Dominik Brodowski <linux@brodo.de>
7 *
8 * (C) 2006-2007 Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
9 * Shaohua Li <shaohua.li@intel.com>
10 * Adam Belay <abelay@novell.com>
11 *
12 * This code is licenced under the GPL.
13 */
14
15#include <linux/kernel.h>
16#include <linux/cpuidle.h>
17#include <linux/jiffies.h>
18#include <linux/tick.h>
19
20#include <asm/io.h>
21#include <linux/uaccess.h>
22
23#define PROMOTION_COUNT 4
24#define DEMOTION_COUNT 1
25
26struct ladder_device_state {
27 struct {
28 u32 promotion_count;
29 u32 demotion_count;
30 u64 promotion_time_ns;
31 u64 demotion_time_ns;
32 } threshold;
33 struct {
34 int promotion_count;
35 int demotion_count;
36 } stats;
37};
38
39struct ladder_device {
40 struct ladder_device_state states[CPUIDLE_STATE_MAX];
41};
42
43static DEFINE_PER_CPU(struct ladder_device, ladder_devices);
44
45/**
46 * ladder_do_selection - prepares private data for a state change
47 * @ldev: the ladder device
48 * @old_idx: the current state index
49 * @new_idx: the new target state index
50 */
51static inline void ladder_do_selection(struct cpuidle_device *dev,
52 struct ladder_device *ldev,
53 int old_idx, int new_idx)
54{
55 ldev->states[old_idx].stats.promotion_count = 0;
56 ldev->states[old_idx].stats.demotion_count = 0;
57 dev->last_state_idx = new_idx;
58}
59
60/**
61 * ladder_select_state - selects the next state to enter
62 * @drv: cpuidle driver
63 * @dev: the CPU
64 * @dummy: not used
65 */
66static int ladder_select_state(struct cpuidle_driver *drv,
67 struct cpuidle_device *dev, bool *dummy)
68{
69 struct ladder_device *ldev = this_cpu_ptr(&ladder_devices);
70 struct ladder_device_state *last_state;
71 int last_idx = dev->last_state_idx;
72 int first_idx = drv->states[0].flags & CPUIDLE_FLAG_POLLING ? 1 : 0;
73 s64 latency_req = cpuidle_governor_latency_req(cpu: dev->cpu);
74 s64 last_residency;
75
76 /* Special case when user has set very strict latency requirement */
77 if (unlikely(latency_req == 0)) {
78 ladder_do_selection(dev, ldev, old_idx: last_idx, new_idx: 0);
79 return 0;
80 }
81
82 last_state = &ldev->states[last_idx];
83
84 last_residency = dev->last_residency_ns - drv->states[last_idx].exit_latency_ns;
85
86 /* consider promotion */
87 if (last_idx < drv->state_count - 1 &&
88 !dev->states_usage[last_idx + 1].disable &&
89 last_residency > last_state->threshold.promotion_time_ns &&
90 drv->states[last_idx + 1].exit_latency_ns <= latency_req) {
91 last_state->stats.promotion_count++;
92 last_state->stats.demotion_count = 0;
93 if (last_state->stats.promotion_count >= last_state->threshold.promotion_count) {
94 ladder_do_selection(dev, ldev, old_idx: last_idx, new_idx: last_idx + 1);
95 return last_idx + 1;
96 }
97 }
98
99 /* consider demotion */
100 if (last_idx > first_idx &&
101 (dev->states_usage[last_idx].disable ||
102 drv->states[last_idx].exit_latency_ns > latency_req)) {
103 int i;
104
105 for (i = last_idx - 1; i > first_idx; i--) {
106 if (drv->states[i].exit_latency_ns <= latency_req)
107 break;
108 }
109 ladder_do_selection(dev, ldev, old_idx: last_idx, new_idx: i);
110 return i;
111 }
112
113 if (last_idx > first_idx &&
114 last_residency < last_state->threshold.demotion_time_ns) {
115 last_state->stats.demotion_count++;
116 last_state->stats.promotion_count = 0;
117 if (last_state->stats.demotion_count >= last_state->threshold.demotion_count) {
118 ladder_do_selection(dev, ldev, old_idx: last_idx, new_idx: last_idx - 1);
119 return last_idx - 1;
120 }
121 }
122
123 /* otherwise remain at the current state */
124 return last_idx;
125}
126
127/**
128 * ladder_enable_device - setup for the governor
129 * @drv: cpuidle driver
130 * @dev: the CPU
131 */
132static int ladder_enable_device(struct cpuidle_driver *drv,
133 struct cpuidle_device *dev)
134{
135 int i;
136 int first_idx = drv->states[0].flags & CPUIDLE_FLAG_POLLING ? 1 : 0;
137 struct ladder_device *ldev = &per_cpu(ladder_devices, dev->cpu);
138 struct ladder_device_state *lstate;
139 struct cpuidle_state *state;
140
141 dev->last_state_idx = first_idx;
142
143 for (i = first_idx; i < drv->state_count; i++) {
144 state = &drv->states[i];
145 lstate = &ldev->states[i];
146
147 lstate->stats.promotion_count = 0;
148 lstate->stats.demotion_count = 0;
149
150 lstate->threshold.promotion_count = PROMOTION_COUNT;
151 lstate->threshold.demotion_count = DEMOTION_COUNT;
152
153 if (i < drv->state_count - 1)
154 lstate->threshold.promotion_time_ns = state->exit_latency_ns;
155 if (i > first_idx)
156 lstate->threshold.demotion_time_ns = state->exit_latency_ns;
157 }
158
159 return 0;
160}
161
162/**
163 * ladder_reflect - update the correct last_state_idx
164 * @dev: the CPU
165 * @index: the index of actual state entered
166 */
167static void ladder_reflect(struct cpuidle_device *dev, int index)
168{
169 if (index > 0)
170 dev->last_state_idx = index;
171}
172
173static struct cpuidle_governor ladder_governor = {
174 .name = "ladder",
175 .rating = 10,
176 .enable = ladder_enable_device,
177 .select = ladder_select_state,
178 .reflect = ladder_reflect,
179};
180
181/**
182 * init_ladder - initializes the governor
183 */
184static int __init init_ladder(void)
185{
186 /*
187 * When NO_HZ is disabled, or when booting with nohz=off, the ladder
188 * governor is better so give it a higher rating than the menu
189 * governor.
190 */
191 if (!tick_nohz_enabled)
192 ladder_governor.rating = 25;
193
194 return cpuidle_register_governor(gov: &ladder_governor);
195}
196
197postcore_initcall(init_ladder);
198

source code of linux/drivers/cpuidle/governors/ladder.c