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 		u32 promotion_time;
31 		u32 demotion_time;
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 	int last_state_idx;
42 };
43 
44 static DEFINE_PER_CPU(struct ladder_device, ladder_devices);
45 
46 /**
47  * ladder_do_selection - prepares private data for a state change
48  * @ldev: the ladder device
49  * @old_idx: the current state index
50  * @new_idx: the new target state index
51  */
52 static inline void ladder_do_selection(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 	ldev->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_residency, last_idx = ldev->last_state_idx;
72 	int first_idx = drv->states[0].flags & CPUIDLE_FLAG_POLLING ? 1 : 0;
73 	int latency_req = cpuidle_governor_latency_req(dev->cpu);
74 
75 	/* Special case when user has set very strict latency requirement */
76 	if (unlikely(latency_req == 0)) {
77 		ladder_do_selection(ldev, last_idx, 0);
78 		return 0;
79 	}
80 
81 	last_state = &ldev->states[last_idx];
82 
83 	last_residency = dev->last_residency - drv->states[last_idx].exit_latency;
84 
85 	/* consider promotion */
86 	if (last_idx < drv->state_count - 1 &&
87 	    !drv->states[last_idx + 1].disabled &&
88 	    !dev->states_usage[last_idx + 1].disable &&
89 	    last_residency > last_state->threshold.promotion_time &&
90 	    drv->states[last_idx + 1].exit_latency <= 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(ldev, last_idx, last_idx + 1);
95 			return last_idx + 1;
96 		}
97 	}
98 
99 	/* consider demotion */
100 	if (last_idx > first_idx &&
101 	    (drv->states[last_idx].disabled ||
102 	    dev->states_usage[last_idx].disable ||
103 	    drv->states[last_idx].exit_latency > latency_req)) {
104 		int i;
105 
106 		for (i = last_idx - 1; i > first_idx; i--) {
107 			if (drv->states[i].exit_latency <= latency_req)
108 				break;
109 		}
110 		ladder_do_selection(ldev, last_idx, i);
111 		return i;
112 	}
113 
114 	if (last_idx > first_idx &&
115 	    last_residency < last_state->threshold.demotion_time) {
116 		last_state->stats.demotion_count++;
117 		last_state->stats.promotion_count = 0;
118 		if (last_state->stats.demotion_count >= last_state->threshold.demotion_count) {
119 			ladder_do_selection(ldev, last_idx, last_idx - 1);
120 			return last_idx - 1;
121 		}
122 	}
123 
124 	/* otherwise remain at the current state */
125 	return last_idx;
126 }
127 
128 /**
129  * ladder_enable_device - setup for the governor
130  * @drv: cpuidle driver
131  * @dev: the CPU
132  */
133 static int ladder_enable_device(struct cpuidle_driver *drv,
134 				struct cpuidle_device *dev)
135 {
136 	int i;
137 	int first_idx = drv->states[0].flags & CPUIDLE_FLAG_POLLING ? 1 : 0;
138 	struct ladder_device *ldev = &per_cpu(ladder_devices, dev->cpu);
139 	struct ladder_device_state *lstate;
140 	struct cpuidle_state *state;
141 
142 	ldev->last_state_idx = first_idx;
143 
144 	for (i = first_idx; i < drv->state_count; i++) {
145 		state = &drv->states[i];
146 		lstate = &ldev->states[i];
147 
148 		lstate->stats.promotion_count = 0;
149 		lstate->stats.demotion_count = 0;
150 
151 		lstate->threshold.promotion_count = PROMOTION_COUNT;
152 		lstate->threshold.demotion_count = DEMOTION_COUNT;
153 
154 		if (i < drv->state_count - 1)
155 			lstate->threshold.promotion_time = state->exit_latency;
156 		if (i > first_idx)
157 			lstate->threshold.demotion_time = state->exit_latency;
158 	}
159 
160 	return 0;
161 }
162 
163 /**
164  * ladder_reflect - update the correct last_state_idx
165  * @dev: the CPU
166  * @index: the index of actual state entered
167  */
168 static void ladder_reflect(struct cpuidle_device *dev, int index)
169 {
170 	struct ladder_device *ldev = this_cpu_ptr(&ladder_devices);
171 	if (index > 0)
172 		ldev->last_state_idx = index;
173 }
174 
175 static struct cpuidle_governor ladder_governor = {
176 	.name =		"ladder",
177 	.rating =	10,
178 	.enable =	ladder_enable_device,
179 	.select =	ladder_select_state,
180 	.reflect =	ladder_reflect,
181 };
182 
183 /**
184  * init_ladder - initializes the governor
185  */
186 static int __init init_ladder(void)
187 {
188 	/*
189 	 * When NO_HZ is disabled, or when booting with nohz=off, the ladder
190 	 * governor is better so give it a higher rating than the menu
191 	 * governor.
192 	 */
193 	if (!tick_nohz_enabled)
194 		ladder_governor.rating = 25;
195 
196 	return cpuidle_register_governor(&ladder_governor);
197 }
198 
199 postcore_initcall(init_ladder);
200