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 | 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 | |
39 | struct ladder_device { |
40 | struct ladder_device_state states[CPUIDLE_STATE_MAX]; |
41 | }; |
42 | |
43 | static 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 | */ |
51 | static 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 | */ |
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_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 | */ |
132 | static 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 | */ |
167 | static void ladder_reflect(struct cpuidle_device *dev, int index) |
168 | { |
169 | if (index > 0) |
170 | dev->last_state_idx = index; |
171 | } |
172 | |
173 | static 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 | */ |
184 | static 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 | |
197 | postcore_initcall(init_ladder); |
198 | |