[go: nahoru, domu]
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
27struct 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
40struct ladder_device {
41	struct ladder_device_state states[CPUIDLE_STATE_MAX];
42	int last_state_idx;
43};
44
45static 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 */
53static 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 */
66static 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	if (drv->states[last_idx].flags & CPUIDLE_FLAG_TIME_VALID) {
83		last_residency = cpuidle_get_last_residency(dev) - \
84					 drv->states[last_idx].exit_latency;
85	}
86	else
87		last_residency = last_state->threshold.promotion_time + 1;
88
89	/* consider promotion */
90	if (last_idx < drv->state_count - 1 &&
91	    !drv->states[last_idx + 1].disabled &&
92	    !dev->states_usage[last_idx + 1].disable &&
93	    last_residency > last_state->threshold.promotion_time &&
94	    drv->states[last_idx + 1].exit_latency <= latency_req) {
95		last_state->stats.promotion_count++;
96		last_state->stats.demotion_count = 0;
97		if (last_state->stats.promotion_count >= last_state->threshold.promotion_count) {
98			ladder_do_selection(ldev, last_idx, last_idx + 1);
99			return last_idx + 1;
100		}
101	}
102
103	/* consider demotion */
104	if (last_idx > CPUIDLE_DRIVER_STATE_START &&
105	    (drv->states[last_idx].disabled ||
106	    dev->states_usage[last_idx].disable ||
107	    drv->states[last_idx].exit_latency > latency_req)) {
108		int i;
109
110		for (i = last_idx - 1; i > CPUIDLE_DRIVER_STATE_START; i--) {
111			if (drv->states[i].exit_latency <= latency_req)
112				break;
113		}
114		ladder_do_selection(ldev, last_idx, i);
115		return i;
116	}
117
118	if (last_idx > CPUIDLE_DRIVER_STATE_START &&
119	    last_residency < last_state->threshold.demotion_time) {
120		last_state->stats.demotion_count++;
121		last_state->stats.promotion_count = 0;
122		if (last_state->stats.demotion_count >= last_state->threshold.demotion_count) {
123			ladder_do_selection(ldev, last_idx, last_idx - 1);
124			return last_idx - 1;
125		}
126	}
127
128	/* otherwise remain at the current state */
129	return last_idx;
130}
131
132/**
133 * ladder_enable_device - setup for the governor
134 * @drv: cpuidle driver
135 * @dev: the CPU
136 */
137static int ladder_enable_device(struct cpuidle_driver *drv,
138				struct cpuidle_device *dev)
139{
140	int i;
141	struct ladder_device *ldev = &per_cpu(ladder_devices, dev->cpu);
142	struct ladder_device_state *lstate;
143	struct cpuidle_state *state;
144
145	ldev->last_state_idx = CPUIDLE_DRIVER_STATE_START;
146
147	for (i = CPUIDLE_DRIVER_STATE_START; i < drv->state_count; i++) {
148		state = &drv->states[i];
149		lstate = &ldev->states[i];
150
151		lstate->stats.promotion_count = 0;
152		lstate->stats.demotion_count = 0;
153
154		lstate->threshold.promotion_count = PROMOTION_COUNT;
155		lstate->threshold.demotion_count = DEMOTION_COUNT;
156
157		if (i < drv->state_count - 1)
158			lstate->threshold.promotion_time = state->exit_latency;
159		if (i > CPUIDLE_DRIVER_STATE_START)
160			lstate->threshold.demotion_time = state->exit_latency;
161	}
162
163	return 0;
164}
165
166/**
167 * ladder_reflect - update the correct last_state_idx
168 * @dev: the CPU
169 * @index: the index of actual state entered
170 */
171static void ladder_reflect(struct cpuidle_device *dev, int index)
172{
173	struct ladder_device *ldev = this_cpu_ptr(&ladder_devices);
174	if (index > 0)
175		ldev->last_state_idx = index;
176}
177
178static struct cpuidle_governor ladder_governor = {
179	.name =		"ladder",
180	.rating =	10,
181	.enable =	ladder_enable_device,
182	.select =	ladder_select_state,
183	.reflect =	ladder_reflect,
184	.owner =	THIS_MODULE,
185};
186
187/**
188 * init_ladder - initializes the governor
189 */
190static int __init init_ladder(void)
191{
192	return cpuidle_register_governor(&ladder_governor);
193}
194
195postcore_initcall(init_ladder);
196