12c98900dcf834645f47858f1687a46dbc5857cc
[linux-2.6.git] / drivers / cpuidle / governors / ladder.c
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/pm_qos_params.h>
18 #include <linux/moduleparam.h>
19 #include <linux/jiffies.h>
20
21 #include <asm/io.h>
22 #include <asm/uaccess.h>
23
24 #define PROMOTION_COUNT 4
25 #define DEMOTION_COUNT 1
26
27 struct ladder_device_state {
28         struct {
29                 u32 promotion_count;
30                 u32 demotion_count;
31                 u32 promotion_time;
32                 u32 demotion_time;
33         } threshold;
34         struct {
35                 int promotion_count;
36                 int demotion_count;
37         } stats;
38 };
39
40 struct ladder_device {
41         struct ladder_device_state states[CPUIDLE_STATE_MAX];
42         int last_state_idx;
43 };
44
45 static DEFINE_PER_CPU(struct ladder_device, ladder_devices);
46
47 /**
48  * ladder_do_selection - prepares private data for a state change
49  * @ldev: the ladder device
50  * @old_idx: the current state index
51  * @new_idx: the new target state index
52  */
53 static inline void ladder_do_selection(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         ldev->last_state_idx = new_idx;
59 }
60
61 /**
62  * ladder_select_state - selects the next state to enter
63  * @dev: the CPU
64  */
65 static int ladder_select_state(struct cpuidle_device *dev)
66 {
67         struct ladder_device *ldev = &__get_cpu_var(ladder_devices);
68         struct ladder_device_state *last_state;
69         int last_residency, last_idx = ldev->last_state_idx;
70         int latency_req = pm_qos_request(PM_QOS_CPU_DMA_LATENCY);
71
72         /* Special case when user has set very strict latency requirement */
73         if (unlikely(latency_req == 0)) {
74                 ladder_do_selection(ldev, last_idx, 0);
75                 return 0;
76         }
77
78         last_state = &ldev->states[last_idx];
79
80         if (dev->states[last_idx].flags & CPUIDLE_FLAG_TIME_VALID)
81                 last_residency = cpuidle_get_last_residency(dev) - dev->states[last_idx].exit_latency;
82         else
83                 last_residency = last_state->threshold.promotion_time + 1;
84
85         /* consider promotion */
86         if (last_idx < dev->state_count - 1 &&
87             last_residency > last_state->threshold.promotion_time &&
88             dev->states[last_idx + 1].exit_latency <= latency_req) {
89                 last_state->stats.promotion_count++;
90                 last_state->stats.demotion_count = 0;
91                 if (last_state->stats.promotion_count >= last_state->threshold.promotion_count) {
92                         ladder_do_selection(ldev, last_idx, last_idx + 1);
93                         return last_idx + 1;
94                 }
95         }
96
97         /* consider demotion */
98         if (last_idx > CPUIDLE_DRIVER_STATE_START &&
99             dev->states[last_idx].exit_latency > latency_req) {
100                 int i;
101
102                 for (i = last_idx - 1; i > CPUIDLE_DRIVER_STATE_START; i--) {
103                         if (dev->states[i].exit_latency <= latency_req)
104                                 break;
105                 }
106                 ladder_do_selection(ldev, last_idx, i);
107                 return i;
108         }
109
110         if (last_idx > CPUIDLE_DRIVER_STATE_START &&
111             last_residency < last_state->threshold.demotion_time) {
112                 last_state->stats.demotion_count++;
113                 last_state->stats.promotion_count = 0;
114                 if (last_state->stats.demotion_count >= last_state->threshold.demotion_count) {
115                         ladder_do_selection(ldev, last_idx, last_idx - 1);
116                         return last_idx - 1;
117                 }
118         }
119
120         /* otherwise remain at the current state */
121         return last_idx;
122 }
123
124 /**
125  * ladder_enable_device - setup for the governor
126  * @dev: the CPU
127  */
128 static int ladder_enable_device(struct cpuidle_device *dev)
129 {
130         int i;
131         struct ladder_device *ldev = &per_cpu(ladder_devices, dev->cpu);
132         struct ladder_device_state *lstate;
133         struct cpuidle_state *state;
134
135         ldev->last_state_idx = CPUIDLE_DRIVER_STATE_START;
136
137         for (i = 0; i < dev->state_count; i++) {
138                 state = &dev->states[i];
139                 lstate = &ldev->states[i];
140
141                 lstate->stats.promotion_count = 0;
142                 lstate->stats.demotion_count = 0;
143
144                 lstate->threshold.promotion_count = PROMOTION_COUNT;
145                 lstate->threshold.demotion_count = DEMOTION_COUNT;
146
147                 if (i < dev->state_count - 1)
148                         lstate->threshold.promotion_time = state->exit_latency;
149                 if (i > 0)
150                         lstate->threshold.demotion_time = state->exit_latency;
151         }
152
153         return 0;
154 }
155
156 static struct cpuidle_governor ladder_governor = {
157         .name =         "ladder",
158         .rating =       10,
159         .enable =       ladder_enable_device,
160         .select =       ladder_select_state,
161         .owner =        THIS_MODULE,
162 };
163
164 /**
165  * init_ladder - initializes the governor
166  */
167 static int __init init_ladder(void)
168 {
169         return cpuidle_register_governor(&ladder_governor);
170 }
171
172 /**
173  * exit_ladder - exits the governor
174  */
175 static void __exit exit_ladder(void)
176 {
177         cpuidle_unregister_governor(&ladder_governor);
178 }
179
180 MODULE_LICENSE("GPL");
181 module_init(init_ladder);
182 module_exit(exit_ladder);