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 
71 	if (unlikely(!ldev))
72 		return 0;
73 
74 	last_state = &ldev->states[last_idx];
75 
76 	if (dev->states[last_idx].flags & CPUIDLE_FLAG_TIME_VALID)
77 		last_residency = cpuidle_get_last_residency(dev) - dev->states[last_idx].exit_latency;
78 	else
79 		last_residency = last_state->threshold.promotion_time + 1;
80 
81 	/* consider promotion */
82 	if (last_idx < dev->state_count - 1 &&
83 	    last_residency > last_state->threshold.promotion_time &&
84 	    dev->states[last_idx + 1].exit_latency <=
85 			pm_qos_requirement(PM_QOS_CPU_DMA_LATENCY)) {
86 		last_state->stats.promotion_count++;
87 		last_state->stats.demotion_count = 0;
88 		if (last_state->stats.promotion_count >= last_state->threshold.promotion_count) {
89 			ladder_do_selection(ldev, last_idx, last_idx + 1);
90 			return last_idx + 1;
91 		}
92 	}
93 
94 	/* consider demotion */
95 	if (last_idx > 0 &&
96 	    last_residency < last_state->threshold.demotion_time) {
97 		last_state->stats.demotion_count++;
98 		last_state->stats.promotion_count = 0;
99 		if (last_state->stats.demotion_count >= last_state->threshold.demotion_count) {
100 			ladder_do_selection(ldev, last_idx, last_idx - 1);
101 			return last_idx - 1;
102 		}
103 	}
104 
105 	/* otherwise remain at the current state */
106 	return last_idx;
107 }
108 
109 /**
110  * ladder_enable_device - setup for the governor
111  * @dev: the CPU
112  */
113 static int ladder_enable_device(struct cpuidle_device *dev)
114 {
115 	int i;
116 	struct ladder_device *ldev = &per_cpu(ladder_devices, dev->cpu);
117 	struct ladder_device_state *lstate;
118 	struct cpuidle_state *state;
119 
120 	ldev->last_state_idx = 0;
121 
122 	for (i = 0; i < dev->state_count; i++) {
123 		state = &dev->states[i];
124 		lstate = &ldev->states[i];
125 
126 		lstate->stats.promotion_count = 0;
127 		lstate->stats.demotion_count = 0;
128 
129 		lstate->threshold.promotion_count = PROMOTION_COUNT;
130 		lstate->threshold.demotion_count = DEMOTION_COUNT;
131 
132 		if (i < dev->state_count - 1)
133 			lstate->threshold.promotion_time = state->exit_latency;
134 		if (i > 0)
135 			lstate->threshold.demotion_time = state->exit_latency;
136 	}
137 
138 	return 0;
139 }
140 
141 static struct cpuidle_governor ladder_governor = {
142 	.name =		"ladder",
143 	.rating =	10,
144 	.enable =	ladder_enable_device,
145 	.select =	ladder_select_state,
146 	.owner =	THIS_MODULE,
147 };
148 
149 /**
150  * init_ladder - initializes the governor
151  */
152 static int __init init_ladder(void)
153 {
154 	return cpuidle_register_governor(&ladder_governor);
155 }
156 
157 /**
158  * exit_ladder - exits the governor
159  */
160 static void __exit exit_ladder(void)
161 {
162 	cpuidle_unregister_governor(&ladder_governor);
163 }
164 
165 MODULE_LICENSE("GPL");
166 module_init(init_ladder);
167 module_exit(exit_ladder);
168