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_requirement(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);
183