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 * @dev: the CPU
48 * @ldev: the ladder device
49 * @old_idx: the current state index
50 * @new_idx: the new target state index
51 */
52static inline void ladder_do_selection(struct cpuidle_device *dev,
53 struct ladder_device *ldev,
54 int old_idx, int new_idx)
55{
56 ldev->states[old_idx].stats.promotion_count = 0;
57 ldev->states[old_idx].stats.demotion_count = 0;
58 dev->last_state_idx = new_idx;
59}
60
61/**
62 * ladder_select_state - selects the next state to enter
63 * @drv: cpuidle driver
64 * @dev: the CPU
65 * @dummy: not used
66 */
67static int ladder_select_state(struct cpuidle_driver *drv,
68 struct cpuidle_device *dev, bool *dummy)
69{
70 struct ladder_device *ldev = this_cpu_ptr(&ladder_devices);
71 struct ladder_device_state *last_state;
72 int last_idx = dev->last_state_idx;
73 int first_idx = drv->states[0].flags & CPUIDLE_FLAG_POLLING ? 1 : 0;
74 s64 latency_req = cpuidle_governor_latency_req(cpu: dev->cpu);
75 s64 last_residency;
76
77 /* Special case when user has set very strict latency requirement */
78 if (unlikely(latency_req == 0)) {
79 ladder_do_selection(dev, ldev, old_idx: last_idx, new_idx: 0);
80 return 0;
81 }
82
83 last_state = &ldev->states[last_idx];
84
85 last_residency = dev->last_residency_ns - drv->states[last_idx].exit_latency_ns;
86
87 /* consider promotion */
88 if (last_idx < drv->state_count - 1 &&
89 !dev->states_usage[last_idx + 1].disable &&
90 last_residency > last_state->threshold.promotion_time_ns &&
91 drv->states[last_idx + 1].exit_latency_ns <= latency_req) {
92 last_state->stats.promotion_count++;
93 last_state->stats.demotion_count = 0;
94 if (last_state->stats.promotion_count >= last_state->threshold.promotion_count) {
95 ladder_do_selection(dev, ldev, old_idx: last_idx, new_idx: last_idx + 1);
96 return last_idx + 1;
97 }
98 }
99
100 /* consider demotion */
101 if (last_idx > first_idx &&
102 (dev->states_usage[last_idx].disable ||
103 drv->states[last_idx].exit_latency_ns > latency_req)) {
104 int i;
105
106 for (i = last_idx - 1; i > first_idx; i--) {
107 if (drv->states[i].exit_latency_ns <= latency_req)
108 break;
109 }
110 ladder_do_selection(dev, ldev, old_idx: last_idx, new_idx: i);
111 return i;
112 }
113
114 if (last_idx > first_idx &&
115 last_residency < last_state->threshold.demotion_time_ns) {
116 last_state->stats.demotion_count++;
117 last_state->stats.promotion_count = 0;
118 if (last_state->stats.demotion_count >= last_state->threshold.demotion_count) {
119 ladder_do_selection(dev, ldev, old_idx: last_idx, new_idx: last_idx - 1);
120 return last_idx - 1;
121 }
122 }
123
124 /* otherwise remain at the current state */
125 return last_idx;
126}
127
128/**
129 * ladder_enable_device - setup for the governor
130 * @drv: cpuidle driver
131 * @dev: the CPU
132 */
133static int ladder_enable_device(struct cpuidle_driver *drv,
134 struct cpuidle_device *dev)
135{
136 int i;
137 int first_idx = drv->states[0].flags & CPUIDLE_FLAG_POLLING ? 1 : 0;
138 struct ladder_device *ldev = &per_cpu(ladder_devices, dev->cpu);
139 struct ladder_device_state *lstate;
140 struct cpuidle_state *state;
141
142 dev->last_state_idx = first_idx;
143
144 for (i = first_idx; i < drv->state_count; i++) {
145 state = &drv->states[i];
146 lstate = &ldev->states[i];
147
148 lstate->stats.promotion_count = 0;
149 lstate->stats.demotion_count = 0;
150
151 lstate->threshold.promotion_count = PROMOTION_COUNT;
152 lstate->threshold.demotion_count = DEMOTION_COUNT;
153
154 if (i < drv->state_count - 1)
155 lstate->threshold.promotion_time_ns = state->exit_latency_ns;
156 if (i > first_idx)
157 lstate->threshold.demotion_time_ns = state->exit_latency_ns;
158 }
159
160 return 0;
161}
162
163/**
164 * ladder_reflect - update the correct last_state_idx
165 * @dev: the CPU
166 * @index: the index of actual state entered
167 */
168static void ladder_reflect(struct cpuidle_device *dev, int index)
169{
170 if (index > 0)
171 dev->last_state_idx = index;
172}
173
174static struct cpuidle_governor ladder_governor = {
175 .name = "ladder",
176 .rating = 10,
177 .enable = ladder_enable_device,
178 .select = ladder_select_state,
179 .reflect = ladder_reflect,
180};
181
182/**
183 * init_ladder - initializes the governor
184 */
185static int __init init_ladder(void)
186{
187 /*
188 * When NO_HZ is disabled, or when booting with nohz=off, the ladder
189 * governor is better so give it a higher rating than the menu
190 * governor.
191 */
192 if (!tick_nohz_enabled)
193 ladder_governor.rating = 25;
194
195 return cpuidle_register_governor(gov: &ladder_governor);
196}
197
198postcore_initcall(init_ladder);
199

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