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1 | /* |
2 | * menu.c - the menu idle governor | |
3 | * | |
4 | * Copyright (C) 2006-2007 Adam Belay <abelay@novell.com> | |
69d25870 AV |
5 | * Copyright (C) 2009 Intel Corporation |
6 | * Author: | |
7 | * Arjan van de Ven <arjan@linux.intel.com> | |
4f86d3a8 | 8 | * |
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9 | * This code is licenced under the GPL version 2 as described |
10 | * in the COPYING file that acompanies the Linux Kernel. | |
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11 | */ |
12 | ||
13 | #include <linux/kernel.h> | |
14 | #include <linux/cpuidle.h> | |
d82b3518 | 15 | #include <linux/pm_qos_params.h> |
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16 | #include <linux/time.h> |
17 | #include <linux/ktime.h> | |
18 | #include <linux/hrtimer.h> | |
19 | #include <linux/tick.h> | |
69d25870 | 20 | #include <linux/sched.h> |
4f86d3a8 | 21 | |
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22 | #define BUCKETS 12 |
23 | #define RESOLUTION 1024 | |
24 | #define DECAY 4 | |
25 | #define MAX_INTERESTING 50000 | |
26 | ||
27 | /* | |
28 | * Concepts and ideas behind the menu governor | |
29 | * | |
30 | * For the menu governor, there are 3 decision factors for picking a C | |
31 | * state: | |
32 | * 1) Energy break even point | |
33 | * 2) Performance impact | |
34 | * 3) Latency tolerance (from pmqos infrastructure) | |
35 | * These these three factors are treated independently. | |
36 | * | |
37 | * Energy break even point | |
38 | * ----------------------- | |
39 | * C state entry and exit have an energy cost, and a certain amount of time in | |
40 | * the C state is required to actually break even on this cost. CPUIDLE | |
41 | * provides us this duration in the "target_residency" field. So all that we | |
42 | * need is a good prediction of how long we'll be idle. Like the traditional | |
43 | * menu governor, we start with the actual known "next timer event" time. | |
44 | * | |
45 | * Since there are other source of wakeups (interrupts for example) than | |
46 | * the next timer event, this estimation is rather optimistic. To get a | |
47 | * more realistic estimate, a correction factor is applied to the estimate, | |
48 | * that is based on historic behavior. For example, if in the past the actual | |
49 | * duration always was 50% of the next timer tick, the correction factor will | |
50 | * be 0.5. | |
51 | * | |
52 | * menu uses a running average for this correction factor, however it uses a | |
53 | * set of factors, not just a single factor. This stems from the realization | |
54 | * that the ratio is dependent on the order of magnitude of the expected | |
55 | * duration; if we expect 500 milliseconds of idle time the likelihood of | |
56 | * getting an interrupt very early is much higher than if we expect 50 micro | |
57 | * seconds of idle time. A second independent factor that has big impact on | |
58 | * the actual factor is if there is (disk) IO outstanding or not. | |
59 | * (as a special twist, we consider every sleep longer than 50 milliseconds | |
60 | * as perfect; there are no power gains for sleeping longer than this) | |
61 | * | |
62 | * For these two reasons we keep an array of 12 independent factors, that gets | |
63 | * indexed based on the magnitude of the expected duration as well as the | |
64 | * "is IO outstanding" property. | |
65 | * | |
66 | * Limiting Performance Impact | |
67 | * --------------------------- | |
68 | * C states, especially those with large exit latencies, can have a real | |
69 | * noticable impact on workloads, which is not acceptable for most sysadmins, | |
70 | * and in addition, less performance has a power price of its own. | |
71 | * | |
72 | * As a general rule of thumb, menu assumes that the following heuristic | |
73 | * holds: | |
74 | * The busier the system, the less impact of C states is acceptable | |
75 | * | |
76 | * This rule-of-thumb is implemented using a performance-multiplier: | |
77 | * If the exit latency times the performance multiplier is longer than | |
78 | * the predicted duration, the C state is not considered a candidate | |
79 | * for selection due to a too high performance impact. So the higher | |
80 | * this multiplier is, the longer we need to be idle to pick a deep C | |
81 | * state, and thus the less likely a busy CPU will hit such a deep | |
82 | * C state. | |
83 | * | |
84 | * Two factors are used in determing this multiplier: | |
85 | * a value of 10 is added for each point of "per cpu load average" we have. | |
86 | * a value of 5 points is added for each process that is waiting for | |
87 | * IO on this CPU. | |
88 | * (these values are experimentally determined) | |
89 | * | |
90 | * The load average factor gives a longer term (few seconds) input to the | |
91 | * decision, while the iowait value gives a cpu local instantanious input. | |
92 | * The iowait factor may look low, but realize that this is also already | |
93 | * represented in the system load average. | |
94 | * | |
95 | */ | |
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96 | |
97 | struct menu_device { | |
98 | int last_state_idx; | |
99 | ||
100 | unsigned int expected_us; | |
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101 | u64 predicted_us; |
102 | unsigned int measured_us; | |
103 | unsigned int exit_us; | |
104 | unsigned int bucket; | |
105 | u64 correction_factor[BUCKETS]; | |
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106 | }; |
107 | ||
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108 | |
109 | #define LOAD_INT(x) ((x) >> FSHIFT) | |
110 | #define LOAD_FRAC(x) LOAD_INT(((x) & (FIXED_1-1)) * 100) | |
111 | ||
112 | static int get_loadavg(void) | |
113 | { | |
114 | unsigned long this = this_cpu_load(); | |
115 | ||
116 | ||
117 | return LOAD_INT(this) * 10 + LOAD_FRAC(this) / 10; | |
118 | } | |
119 | ||
120 | static inline int which_bucket(unsigned int duration) | |
121 | { | |
122 | int bucket = 0; | |
123 | ||
124 | /* | |
125 | * We keep two groups of stats; one with no | |
126 | * IO pending, one without. | |
127 | * This allows us to calculate | |
128 | * E(duration)|iowait | |
129 | */ | |
130 | if (nr_iowait_cpu()) | |
131 | bucket = BUCKETS/2; | |
132 | ||
133 | if (duration < 10) | |
134 | return bucket; | |
135 | if (duration < 100) | |
136 | return bucket + 1; | |
137 | if (duration < 1000) | |
138 | return bucket + 2; | |
139 | if (duration < 10000) | |
140 | return bucket + 3; | |
141 | if (duration < 100000) | |
142 | return bucket + 4; | |
143 | return bucket + 5; | |
144 | } | |
145 | ||
146 | /* | |
147 | * Return a multiplier for the exit latency that is intended | |
148 | * to take performance requirements into account. | |
149 | * The more performance critical we estimate the system | |
150 | * to be, the higher this multiplier, and thus the higher | |
151 | * the barrier to go to an expensive C state. | |
152 | */ | |
153 | static inline int performance_multiplier(void) | |
154 | { | |
155 | int mult = 1; | |
156 | ||
157 | /* for higher loadavg, we are more reluctant */ | |
158 | ||
159 | mult += 2 * get_loadavg(); | |
160 | ||
161 | /* for IO wait tasks (per cpu!) we add 5x each */ | |
162 | mult += 10 * nr_iowait_cpu(); | |
163 | ||
164 | return mult; | |
165 | } | |
166 | ||
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167 | static DEFINE_PER_CPU(struct menu_device, menu_devices); |
168 | ||
169 | /** | |
170 | * menu_select - selects the next idle state to enter | |
171 | * @dev: the CPU | |
172 | */ | |
173 | static int menu_select(struct cpuidle_device *dev) | |
174 | { | |
175 | struct menu_device *data = &__get_cpu_var(menu_devices); | |
a2bd9202 | 176 | int latency_req = pm_qos_requirement(PM_QOS_CPU_DMA_LATENCY); |
4f86d3a8 | 177 | int i; |
69d25870 AV |
178 | int multiplier; |
179 | ||
180 | data->last_state_idx = 0; | |
181 | data->exit_us = 0; | |
4f86d3a8 | 182 | |
a2bd9202 | 183 | /* Special case when user has set very strict latency requirement */ |
69d25870 | 184 | if (unlikely(latency_req == 0)) |
a2bd9202 | 185 | return 0; |
a2bd9202 | 186 | |
69d25870 | 187 | /* determine the expected residency time, round up */ |
4f86d3a8 | 188 | data->expected_us = |
69d25870 AV |
189 | DIV_ROUND_UP((u32)ktime_to_ns(tick_nohz_get_sleep_length()), 1000); |
190 | ||
191 | ||
192 | data->bucket = which_bucket(data->expected_us); | |
193 | ||
194 | multiplier = performance_multiplier(); | |
195 | ||
196 | /* | |
197 | * if the correction factor is 0 (eg first time init or cpu hotplug | |
198 | * etc), we actually want to start out with a unity factor. | |
199 | */ | |
200 | if (data->correction_factor[data->bucket] == 0) | |
201 | data->correction_factor[data->bucket] = RESOLUTION * DECAY; | |
202 | ||
203 | /* Make sure to round up for half microseconds */ | |
204 | data->predicted_us = DIV_ROUND_CLOSEST( | |
205 | data->expected_us * data->correction_factor[data->bucket], | |
206 | RESOLUTION * DECAY); | |
207 | ||
208 | /* | |
209 | * We want to default to C1 (hlt), not to busy polling | |
210 | * unless the timer is happening really really soon. | |
211 | */ | |
212 | if (data->expected_us > 5) | |
213 | data->last_state_idx = CPUIDLE_DRIVER_STATE_START; | |
4f86d3a8 | 214 | |
816bb611 | 215 | |
4f86d3a8 | 216 | /* find the deepest idle state that satisfies our constraints */ |
69d25870 | 217 | for (i = CPUIDLE_DRIVER_STATE_START; i < dev->state_count; i++) { |
4f86d3a8 LB |
218 | struct cpuidle_state *s = &dev->states[i]; |
219 | ||
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220 | if (s->target_residency > data->predicted_us) |
221 | break; | |
a2bd9202 | 222 | if (s->exit_latency > latency_req) |
4f86d3a8 | 223 | break; |
69d25870 AV |
224 | if (s->exit_latency * multiplier > data->predicted_us) |
225 | break; | |
226 | data->exit_us = s->exit_latency; | |
227 | data->last_state_idx = i; | |
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228 | } |
229 | ||
69d25870 | 230 | return data->last_state_idx; |
4f86d3a8 LB |
231 | } |
232 | ||
233 | /** | |
234 | * menu_reflect - attempts to guess what happened after entry | |
235 | * @dev: the CPU | |
236 | * | |
237 | * NOTE: it's important to be fast here because this operation will add to | |
238 | * the overall exit latency. | |
239 | */ | |
240 | static void menu_reflect(struct cpuidle_device *dev) | |
241 | { | |
242 | struct menu_device *data = &__get_cpu_var(menu_devices); | |
243 | int last_idx = data->last_state_idx; | |
320eee77 | 244 | unsigned int last_idle_us = cpuidle_get_last_residency(dev); |
4f86d3a8 | 245 | struct cpuidle_state *target = &dev->states[last_idx]; |
320eee77 | 246 | unsigned int measured_us; |
69d25870 | 247 | u64 new_factor; |
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248 | |
249 | /* | |
250 | * Ugh, this idle state doesn't support residency measurements, so we | |
251 | * are basically lost in the dark. As a compromise, assume we slept | |
69d25870 | 252 | * for the whole expected time. |
4f86d3a8 | 253 | */ |
320eee77 | 254 | if (unlikely(!(target->flags & CPUIDLE_FLAG_TIME_VALID))) |
69d25870 AV |
255 | last_idle_us = data->expected_us; |
256 | ||
257 | ||
258 | measured_us = last_idle_us; | |
4f86d3a8 | 259 | |
320eee77 | 260 | /* |
69d25870 AV |
261 | * We correct for the exit latency; we are assuming here that the |
262 | * exit latency happens after the event that we're interested in. | |
320eee77 | 263 | */ |
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264 | if (measured_us > data->exit_us) |
265 | measured_us -= data->exit_us; | |
266 | ||
267 | ||
268 | /* update our correction ratio */ | |
269 | ||
270 | new_factor = data->correction_factor[data->bucket] | |
271 | * (DECAY - 1) / DECAY; | |
272 | ||
273 | if (data->expected_us > 0 && data->measured_us < MAX_INTERESTING) | |
274 | new_factor += RESOLUTION * measured_us / data->expected_us; | |
320eee77 | 275 | else |
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276 | /* |
277 | * we were idle so long that we count it as a perfect | |
278 | * prediction | |
279 | */ | |
280 | new_factor += RESOLUTION; | |
320eee77 | 281 | |
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282 | /* |
283 | * We don't want 0 as factor; we always want at least | |
284 | * a tiny bit of estimated time. | |
285 | */ | |
286 | if (new_factor == 0) | |
287 | new_factor = 1; | |
320eee77 | 288 | |
69d25870 | 289 | data->correction_factor[data->bucket] = new_factor; |
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290 | } |
291 | ||
292 | /** | |
293 | * menu_enable_device - scans a CPU's states and does setup | |
294 | * @dev: the CPU | |
295 | */ | |
296 | static int menu_enable_device(struct cpuidle_device *dev) | |
297 | { | |
298 | struct menu_device *data = &per_cpu(menu_devices, dev->cpu); | |
299 | ||
300 | memset(data, 0, sizeof(struct menu_device)); | |
301 | ||
302 | return 0; | |
303 | } | |
304 | ||
305 | static struct cpuidle_governor menu_governor = { | |
306 | .name = "menu", | |
307 | .rating = 20, | |
308 | .enable = menu_enable_device, | |
309 | .select = menu_select, | |
310 | .reflect = menu_reflect, | |
311 | .owner = THIS_MODULE, | |
312 | }; | |
313 | ||
314 | /** | |
315 | * init_menu - initializes the governor | |
316 | */ | |
317 | static int __init init_menu(void) | |
318 | { | |
319 | return cpuidle_register_governor(&menu_governor); | |
320 | } | |
321 | ||
322 | /** | |
323 | * exit_menu - exits the governor | |
324 | */ | |
325 | static void __exit exit_menu(void) | |
326 | { | |
327 | cpuidle_unregister_governor(&menu_governor); | |
328 | } | |
329 | ||
330 | MODULE_LICENSE("GPL"); | |
331 | module_init(init_menu); | |
332 | module_exit(exit_menu); |