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.h>
18 #include <linux/module.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  * @drv: cpuidle driver
64  * @dev: the CPU
65  */
66 static int ladder_select_state(struct cpuidle_driver *drv,
67 				struct cpuidle_device *dev)
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 latency_req = pm_qos_request(PM_QOS_CPU_DMA_LATENCY);
73 
74 	/* Special case when user has set very strict latency requirement */
75 	if (unlikely(latency_req == 0)) {
76 		ladder_do_selection(ldev, last_idx, 0);
77 		return 0;
78 	}
79 
80 	last_state = &ldev->states[last_idx];
81 
82 	last_residency = cpuidle_get_last_residency(dev) - drv->states[last_idx].exit_latency;
83 
84 	/* consider promotion */
85 	if (last_idx < drv->state_count - 1 &&
86 	    !drv->states[last_idx + 1].disabled &&
87 	    !dev->states_usage[last_idx + 1].disable &&
88 	    last_residency > last_state->threshold.promotion_time &&
89 	    drv->states[last_idx + 1].exit_latency <= latency_req) {
90 		last_state->stats.promotion_count++;
91 		last_state->stats.demotion_count = 0;
92 		if (last_state->stats.promotion_count >= last_state->threshold.promotion_count) {
93 			ladder_do_selection(ldev, last_idx, last_idx + 1);
94 			return last_idx + 1;
95 		}
96 	}
97 
98 	/* consider demotion */
99 	if (last_idx > CPUIDLE_DRIVER_STATE_START &&
100 	    (drv->states[last_idx].disabled ||
101 	    dev->states_usage[last_idx].disable ||
102 	    drv->states[last_idx].exit_latency > latency_req)) {
103 		int i;
104 
105 		for (i = last_idx - 1; i > CPUIDLE_DRIVER_STATE_START; i--) {
106 			if (drv->states[i].exit_latency <= latency_req)
107 				break;
108 		}
109 		ladder_do_selection(ldev, last_idx, i);
110 		return i;
111 	}
112 
113 	if (last_idx > CPUIDLE_DRIVER_STATE_START &&
114 	    last_residency < last_state->threshold.demotion_time) {
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(ldev, last_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 	struct ladder_device *ldev = &per_cpu(ladder_devices, dev->cpu);
137 	struct ladder_device_state *lstate;
138 	struct cpuidle_state *state;
139 
140 	ldev->last_state_idx = CPUIDLE_DRIVER_STATE_START;
141 
142 	for (i = CPUIDLE_DRIVER_STATE_START; i < drv->state_count; i++) {
143 		state = &drv->states[i];
144 		lstate = &ldev->states[i];
145 
146 		lstate->stats.promotion_count = 0;
147 		lstate->stats.demotion_count = 0;
148 
149 		lstate->threshold.promotion_count = PROMOTION_COUNT;
150 		lstate->threshold.demotion_count = DEMOTION_COUNT;
151 
152 		if (i < drv->state_count - 1)
153 			lstate->threshold.promotion_time = state->exit_latency;
154 		if (i > CPUIDLE_DRIVER_STATE_START)
155 			lstate->threshold.demotion_time = state->exit_latency;
156 	}
157 
158 	return 0;
159 }
160 
161 /**
162  * ladder_reflect - update the correct last_state_idx
163  * @dev: the CPU
164  * @index: the index of actual state entered
165  */
166 static void ladder_reflect(struct cpuidle_device *dev, int index)
167 {
168 	struct ladder_device *ldev = this_cpu_ptr(&ladder_devices);
169 	if (index > 0)
170 		ldev->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 	.owner =	THIS_MODULE,
180 };
181 
182 /**
183  * init_ladder - initializes the governor
184  */
185 static int __init init_ladder(void)
186 {
187 	return cpuidle_register_governor(&ladder_governor);
188 }
189 
190 postcore_initcall(init_ladder);
191