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
26 struct ladder_device_state {
27 struct {
28 u32 promotion_count;
29 u32 demotion_count;
30 u32 promotion_time;
31 u32 demotion_time;
32 } threshold;
33 struct {
34 int promotion_count;
35 int demotion_count;
36 } stats;
37 };
38
39 struct ladder_device {
40 struct ladder_device_state states[CPUIDLE_STATE_MAX];
41 int last_state_idx;
42 };
43
44 static DEFINE_PER_CPU(struct ladder_device, ladder_devices);
45
46 /**
47 * ladder_do_selection - prepares private data for a state change
48 * @ldev: the ladder device
49 * @old_idx: the current state index
50 * @new_idx: the new target state index
51 */
ladder_do_selection(struct ladder_device * ldev,int old_idx,int new_idx)52 static inline void ladder_do_selection(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 ldev->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 */
ladder_select_state(struct cpuidle_driver * drv,struct cpuidle_device * dev,bool * dummy)66 static 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_residency, last_idx = ldev->last_state_idx;
72 int first_idx = drv->states[0].flags & CPUIDLE_FLAG_POLLING ? 1 : 0;
73 int latency_req = cpuidle_governor_latency_req(dev->cpu);
74
75 /* Special case when user has set very strict latency requirement */
76 if (unlikely(latency_req == 0)) {
77 ladder_do_selection(ldev, last_idx, 0);
78 return 0;
79 }
80
81 last_state = &ldev->states[last_idx];
82
83 last_residency = cpuidle_get_last_residency(dev) - drv->states[last_idx].exit_latency;
84
85 /* consider promotion */
86 if (last_idx < drv->state_count - 1 &&
87 !drv->states[last_idx + 1].disabled &&
88 !dev->states_usage[last_idx + 1].disable &&
89 last_residency > last_state->threshold.promotion_time &&
90 drv->states[last_idx + 1].exit_latency <= 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(ldev, last_idx, last_idx + 1);
95 return last_idx + 1;
96 }
97 }
98
99 /* consider demotion */
100 if (last_idx > first_idx &&
101 (drv->states[last_idx].disabled ||
102 dev->states_usage[last_idx].disable ||
103 drv->states[last_idx].exit_latency > latency_req)) {
104 int i;
105
106 for (i = last_idx - 1; i > first_idx; i--) {
107 if (drv->states[i].exit_latency <= latency_req)
108 break;
109 }
110 ladder_do_selection(ldev, last_idx, i);
111 return i;
112 }
113
114 if (last_idx > first_idx &&
115 last_residency < last_state->threshold.demotion_time) {
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(ldev, last_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 */
ladder_enable_device(struct cpuidle_driver * drv,struct cpuidle_device * dev)133 static 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 ldev->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 = state->exit_latency;
156 if (i > first_idx)
157 lstate->threshold.demotion_time = state->exit_latency;
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 */
ladder_reflect(struct cpuidle_device * dev,int index)168 static void ladder_reflect(struct cpuidle_device *dev, int index)
169 {
170 struct ladder_device *ldev = this_cpu_ptr(&ladder_devices);
171 if (index > 0)
172 ldev->last_state_idx = index;
173 }
174
175 static struct cpuidle_governor ladder_governor = {
176 .name = "ladder",
177 .rating = 10,
178 .enable = ladder_enable_device,
179 .select = ladder_select_state,
180 .reflect = ladder_reflect,
181 };
182
183 /**
184 * init_ladder - initializes the governor
185 */
init_ladder(void)186 static int __init init_ladder(void)
187 {
188 /*
189 * When NO_HZ is disabled, or when booting with nohz=off, the ladder
190 * governor is better so give it a higher rating than the menu
191 * governor.
192 */
193 if (!tick_nohz_enabled)
194 ladder_governor.rating = 25;
195
196 return cpuidle_register_governor(&ladder_governor);
197 }
198
199 postcore_initcall(init_ladder);
200