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
26struct 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
39struct ladder_device {
40	struct ladder_device_state states[CPUIDLE_STATE_MAX];
41};
42
43static 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 */
51static 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 */
66static 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 */
132static 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 */
167static void ladder_reflect(struct cpuidle_device *dev, int index)
168{
169	if (index > 0)
170		dev->last_state_idx = index;
171}
172
173static 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 */
184static 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
197postcore_initcall(init_ladder);
198