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 		u64 promotion_time_ns;
31 		u64 demotion_time_ns;
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 };
42 
43 static DEFINE_PER_CPU(struct ladder_device, ladder_devices);
44 
45 /**
46  * ladder_do_selection - prepares private data for a state change
47  * @ldev: the ladder device
48  * @old_idx: the current state index
49  * @new_idx: the new target state index
50  */
ladder_do_selection(struct cpuidle_device * dev,struct ladder_device * ldev,int old_idx,int new_idx)51 static inline void ladder_do_selection(struct cpuidle_device *dev,
52 				       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 	dev->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  */
ladder_select_state(struct cpuidle_driver * drv,struct cpuidle_device * dev,bool * dummy)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_idx = dev->last_state_idx;
72 	int first_idx = drv->states[0].flags & CPUIDLE_FLAG_POLLING ? 1 : 0;
73 	s64 latency_req = cpuidle_governor_latency_req(dev->cpu);
74 	s64 last_residency;
75 
76 	/* Special case when user has set very strict latency requirement */
77 	if (unlikely(latency_req == 0)) {
78 		ladder_do_selection(dev, ldev, last_idx, 0);
79 		return 0;
80 	}
81 
82 	last_state = &ldev->states[last_idx];
83 
84 	last_residency = dev->last_residency_ns - drv->states[last_idx].exit_latency_ns;
85 
86 	/* consider promotion */
87 	if (last_idx < drv->state_count - 1 &&
88 	    !dev->states_usage[last_idx + 1].disable &&
89 	    last_residency > last_state->threshold.promotion_time_ns &&
90 	    drv->states[last_idx + 1].exit_latency_ns <= 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(dev, ldev, last_idx, last_idx + 1);
95 			return last_idx + 1;
96 		}
97 	}
98 
99 	/* consider demotion */
100 	if (last_idx > first_idx &&
101 	    (dev->states_usage[last_idx].disable ||
102 	    drv->states[last_idx].exit_latency_ns > latency_req)) {
103 		int i;
104 
105 		for (i = last_idx - 1; i > first_idx; i--) {
106 			if (drv->states[i].exit_latency_ns <= latency_req)
107 				break;
108 		}
109 		ladder_do_selection(dev, ldev, last_idx, i);
110 		return i;
111 	}
112 
113 	if (last_idx > first_idx &&
114 	    last_residency < last_state->threshold.demotion_time_ns) {
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(dev, 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  */
ladder_enable_device(struct cpuidle_driver * drv,struct cpuidle_device * dev)132 static int ladder_enable_device(struct cpuidle_driver *drv,
133 				struct cpuidle_device *dev)
134 {
135 	int i;
136 	int first_idx = drv->states[0].flags & CPUIDLE_FLAG_POLLING ? 1 : 0;
137 	struct ladder_device *ldev = &per_cpu(ladder_devices, dev->cpu);
138 	struct ladder_device_state *lstate;
139 	struct cpuidle_state *state;
140 
141 	dev->last_state_idx = first_idx;
142 
143 	for (i = first_idx; i < drv->state_count; i++) {
144 		state = &drv->states[i];
145 		lstate = &ldev->states[i];
146 
147 		lstate->stats.promotion_count = 0;
148 		lstate->stats.demotion_count = 0;
149 
150 		lstate->threshold.promotion_count = PROMOTION_COUNT;
151 		lstate->threshold.demotion_count = DEMOTION_COUNT;
152 
153 		if (i < drv->state_count - 1)
154 			lstate->threshold.promotion_time_ns = state->exit_latency_ns;
155 		if (i > first_idx)
156 			lstate->threshold.demotion_time_ns = state->exit_latency_ns;
157 	}
158 
159 	return 0;
160 }
161 
162 /**
163  * ladder_reflect - update the correct last_state_idx
164  * @dev: the CPU
165  * @index: the index of actual state entered
166  */
ladder_reflect(struct cpuidle_device * dev,int index)167 static void ladder_reflect(struct cpuidle_device *dev, int index)
168 {
169 	if (index > 0)
170 		dev->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 };
180 
181 /**
182  * init_ladder - initializes the governor
183  */
init_ladder(void)184 static int __init init_ladder(void)
185 {
186 	/*
187 	 * When NO_HZ is disabled, or when booting with nohz=off, the ladder
188 	 * governor is better so give it a higher rating than the menu
189 	 * governor.
190 	 */
191 	if (!tick_nohz_enabled)
192 		ladder_governor.rating = 25;
193 
194 	return cpuidle_register_governor(&ladder_governor);
195 }
196 
197 postcore_initcall(init_ladder);
198