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1 | // SPDX-License-Identifier: GPL-2.0 |
2 | /* | |
3 | * Copyright 2018 Linaro Limited | |
4 | * | |
5 | * Author: Daniel Lezcano <daniel.lezcano@linaro.org> | |
6 | * | |
7 | * The idle injection framework provides a way to force CPUs to enter idle | |
8 | * states for a specified fraction of time over a specified period. | |
9 | * | |
10 | * It relies on the smpboot kthreads feature providing common code for CPU | |
11 | * hotplug and thread [un]parking. | |
12 | * | |
13 | * All of the kthreads used for idle injection are created at init time. | |
14 | * | |
15 | * Next, the users of the the idle injection framework provide a cpumask via | |
16 | * its register function. The kthreads will be synchronized with respect to | |
17 | * this cpumask. | |
18 | * | |
19 | * The idle + run duration is specified via separate helpers and that allows | |
20 | * idle injection to be started. | |
21 | * | |
22 | * The idle injection kthreads will call play_idle() with the idle duration | |
23 | * specified as per the above. | |
24 | * | |
25 | * After all of them have been woken up, a timer is set to start the next idle | |
26 | * injection cycle. | |
27 | * | |
28 | * The timer interrupt handler will wake up the idle injection kthreads for | |
29 | * all of the CPUs in the cpumask provided by the user. | |
30 | * | |
31 | * Idle injection is stopped synchronously and no leftover idle injection | |
32 | * kthread activity after its completion is guaranteed. | |
33 | * | |
34 | * It is up to the user of this framework to provide a lock for higher-level | |
35 | * synchronization to prevent race conditions like starting idle injection | |
36 | * while unregistering from the framework. | |
37 | */ | |
38 | #define pr_fmt(fmt) "ii_dev: " fmt | |
39 | ||
40 | #include <linux/cpu.h> | |
41 | #include <linux/hrtimer.h> | |
42 | #include <linux/kthread.h> | |
43 | #include <linux/sched.h> | |
44 | #include <linux/slab.h> | |
45 | #include <linux/smpboot.h> | |
46 | ||
47 | #include <uapi/linux/sched/types.h> | |
48 | ||
49 | /** | |
50 | * struct idle_inject_thread - task on/off switch structure | |
51 | * @tsk: task injecting the idle cycles | |
52 | * @should_run: whether or not to run the task (for the smpboot kthread API) | |
53 | */ | |
54 | struct idle_inject_thread { | |
55 | struct task_struct *tsk; | |
56 | int should_run; | |
57 | }; | |
58 | ||
59 | /** | |
60 | * struct idle_inject_device - idle injection data | |
61 | * @timer: idle injection period timer | |
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62 | * @idle_duration_us: duration of CPU idle time to inject |
63 | * @run_duration_us: duration of CPU run time to allow | |
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64 | * @cpumask: mask of CPUs affected by idle injection |
65 | */ | |
66 | struct idle_inject_device { | |
67 | struct hrtimer timer; | |
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68 | unsigned int idle_duration_us; |
69 | unsigned int run_duration_us; | |
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70 | unsigned long int cpumask[0]; |
71 | }; | |
72 | ||
73 | static DEFINE_PER_CPU(struct idle_inject_thread, idle_inject_thread); | |
74 | static DEFINE_PER_CPU(struct idle_inject_device *, idle_inject_device); | |
75 | ||
76 | /** | |
77 | * idle_inject_wakeup - Wake up idle injection threads | |
78 | * @ii_dev: target idle injection device | |
79 | * | |
80 | * Every idle injection task associated with the given idle injection device | |
81 | * and running on an online CPU will be woken up. | |
82 | */ | |
83 | static void idle_inject_wakeup(struct idle_inject_device *ii_dev) | |
84 | { | |
85 | struct idle_inject_thread *iit; | |
86 | unsigned int cpu; | |
87 | ||
88 | for_each_cpu_and(cpu, to_cpumask(ii_dev->cpumask), cpu_online_mask) { | |
89 | iit = per_cpu_ptr(&idle_inject_thread, cpu); | |
90 | iit->should_run = 1; | |
91 | wake_up_process(iit->tsk); | |
92 | } | |
93 | } | |
94 | ||
95 | /** | |
96 | * idle_inject_timer_fn - idle injection timer function | |
97 | * @timer: idle injection hrtimer | |
98 | * | |
99 | * This function is called when the idle injection timer expires. It wakes up | |
100 | * idle injection tasks associated with the timer and they, in turn, invoke | |
101 | * play_idle() to inject a specified amount of CPU idle time. | |
102 | * | |
103 | * Return: HRTIMER_RESTART. | |
104 | */ | |
105 | static enum hrtimer_restart idle_inject_timer_fn(struct hrtimer *timer) | |
106 | { | |
cd4c0763 | 107 | unsigned int duration_us; |
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108 | struct idle_inject_device *ii_dev = |
109 | container_of(timer, struct idle_inject_device, timer); | |
110 | ||
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111 | duration_us = READ_ONCE(ii_dev->run_duration_us); |
112 | duration_us += READ_ONCE(ii_dev->idle_duration_us); | |
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113 | |
114 | idle_inject_wakeup(ii_dev); | |
115 | ||
cd4c0763 | 116 | hrtimer_forward_now(timer, ns_to_ktime(duration_us * NSEC_PER_USEC)); |
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117 | |
118 | return HRTIMER_RESTART; | |
119 | } | |
120 | ||
121 | /** | |
122 | * idle_inject_fn - idle injection work function | |
123 | * @cpu: the CPU owning the task | |
124 | * | |
125 | * This function calls play_idle() to inject a specified amount of CPU idle | |
126 | * time. | |
127 | */ | |
128 | static void idle_inject_fn(unsigned int cpu) | |
129 | { | |
130 | struct idle_inject_device *ii_dev; | |
131 | struct idle_inject_thread *iit; | |
132 | ||
133 | ii_dev = per_cpu(idle_inject_device, cpu); | |
134 | iit = per_cpu_ptr(&idle_inject_thread, cpu); | |
135 | ||
136 | /* | |
137 | * Let the smpboot main loop know that the task should not run again. | |
138 | */ | |
139 | iit->should_run = 0; | |
140 | ||
cd4c0763 | 141 | play_idle(READ_ONCE(ii_dev->idle_duration_us)); |
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142 | } |
143 | ||
144 | /** | |
145 | * idle_inject_set_duration - idle and run duration update helper | |
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146 | * @run_duration_us: CPU run time to allow in microseconds |
147 | * @idle_duration_us: CPU idle time to inject in microseconds | |
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148 | */ |
149 | void idle_inject_set_duration(struct idle_inject_device *ii_dev, | |
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150 | unsigned int run_duration_us, |
151 | unsigned int idle_duration_us) | |
88763a5c | 152 | { |
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153 | if (run_duration_us && idle_duration_us) { |
154 | WRITE_ONCE(ii_dev->run_duration_us, run_duration_us); | |
155 | WRITE_ONCE(ii_dev->idle_duration_us, idle_duration_us); | |
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156 | } |
157 | } | |
158 | ||
159 | /** | |
160 | * idle_inject_get_duration - idle and run duration retrieval helper | |
cd4c0763 DL |
161 | * @run_duration_us: memory location to store the current CPU run time |
162 | * @idle_duration_us: memory location to store the current CPU idle time | |
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163 | */ |
164 | void idle_inject_get_duration(struct idle_inject_device *ii_dev, | |
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165 | unsigned int *run_duration_us, |
166 | unsigned int *idle_duration_us) | |
88763a5c | 167 | { |
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168 | *run_duration_us = READ_ONCE(ii_dev->run_duration_us); |
169 | *idle_duration_us = READ_ONCE(ii_dev->idle_duration_us); | |
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170 | } |
171 | ||
172 | /** | |
173 | * idle_inject_start - start idle injections | |
174 | * @ii_dev: idle injection control device structure | |
175 | * | |
176 | * The function starts idle injection by first waking up all of the idle | |
177 | * injection kthreads associated with @ii_dev to let them inject CPU idle time | |
178 | * sets up a timer to start the next idle injection period. | |
179 | * | |
180 | * Return: -EINVAL if the CPU idle or CPU run time is not set or 0 on success. | |
181 | */ | |
182 | int idle_inject_start(struct idle_inject_device *ii_dev) | |
183 | { | |
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184 | unsigned int idle_duration_us = READ_ONCE(ii_dev->idle_duration_us); |
185 | unsigned int run_duration_us = READ_ONCE(ii_dev->run_duration_us); | |
88763a5c | 186 | |
cd4c0763 | 187 | if (!idle_duration_us || !run_duration_us) |
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188 | return -EINVAL; |
189 | ||
190 | pr_debug("Starting injecting idle cycles on CPUs '%*pbl'\n", | |
191 | cpumask_pr_args(to_cpumask(ii_dev->cpumask))); | |
192 | ||
193 | idle_inject_wakeup(ii_dev); | |
194 | ||
195 | hrtimer_start(&ii_dev->timer, | |
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196 | ns_to_ktime((idle_duration_us + run_duration_us) * |
197 | NSEC_PER_USEC), | |
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198 | HRTIMER_MODE_REL); |
199 | ||
200 | return 0; | |
201 | } | |
202 | ||
203 | /** | |
204 | * idle_inject_stop - stops idle injections | |
205 | * @ii_dev: idle injection control device structure | |
206 | * | |
207 | * The function stops idle injection and waits for the threads to finish work. | |
208 | * If CPU idle time is being injected when this function runs, then it will | |
209 | * wait until the end of the cycle. | |
210 | * | |
211 | * When it returns, there is no more idle injection kthread activity. The | |
212 | * kthreads are scheduled out and the periodic timer is off. | |
213 | */ | |
214 | void idle_inject_stop(struct idle_inject_device *ii_dev) | |
215 | { | |
216 | struct idle_inject_thread *iit; | |
217 | unsigned int cpu; | |
218 | ||
219 | pr_debug("Stopping idle injection on CPUs '%*pbl'\n", | |
220 | cpumask_pr_args(to_cpumask(ii_dev->cpumask))); | |
221 | ||
222 | hrtimer_cancel(&ii_dev->timer); | |
223 | ||
224 | /* | |
225 | * Stopping idle injection requires all of the idle injection kthreads | |
226 | * associated with the given cpumask to be parked and stay that way, so | |
227 | * prevent CPUs from going online at this point. Any CPUs going online | |
228 | * after the loop below will be covered by clearing the should_run flag | |
229 | * that will cause the smpboot main loop to schedule them out. | |
230 | */ | |
231 | cpu_hotplug_disable(); | |
232 | ||
233 | /* | |
234 | * Iterate over all (online + offline) CPUs here in case one of them | |
235 | * goes offline with the should_run flag set so as to prevent its idle | |
236 | * injection kthread from running when the CPU goes online again after | |
237 | * the ii_dev has been freed. | |
238 | */ | |
239 | for_each_cpu(cpu, to_cpumask(ii_dev->cpumask)) { | |
240 | iit = per_cpu_ptr(&idle_inject_thread, cpu); | |
241 | iit->should_run = 0; | |
242 | ||
243 | wait_task_inactive(iit->tsk, 0); | |
244 | } | |
245 | ||
246 | cpu_hotplug_enable(); | |
247 | } | |
248 | ||
249 | /** | |
250 | * idle_inject_setup - prepare the current task for idle injection | |
251 | * @cpu: not used | |
252 | * | |
253 | * Called once, this function is in charge of setting the current task's | |
254 | * scheduler parameters to make it an RT task. | |
255 | */ | |
256 | static void idle_inject_setup(unsigned int cpu) | |
257 | { | |
258 | struct sched_param param = { .sched_priority = MAX_USER_RT_PRIO / 2 }; | |
259 | ||
260 | sched_setscheduler(current, SCHED_FIFO, ¶m); | |
261 | } | |
262 | ||
263 | /** | |
264 | * idle_inject_should_run - function helper for the smpboot API | |
265 | * @cpu: CPU the kthread is running on | |
266 | * | |
267 | * Return: whether or not the thread can run. | |
268 | */ | |
269 | static int idle_inject_should_run(unsigned int cpu) | |
270 | { | |
271 | struct idle_inject_thread *iit = | |
272 | per_cpu_ptr(&idle_inject_thread, cpu); | |
273 | ||
274 | return iit->should_run; | |
275 | } | |
276 | ||
277 | /** | |
278 | * idle_inject_register - initialize idle injection on a set of CPUs | |
279 | * @cpumask: CPUs to be affected by idle injection | |
280 | * | |
281 | * This function creates an idle injection control device structure for the | |
282 | * given set of CPUs and initializes the timer associated with it. It does not | |
283 | * start any injection cycles. | |
284 | * | |
285 | * Return: NULL if memory allocation fails, idle injection control device | |
286 | * pointer on success. | |
287 | */ | |
288 | struct idle_inject_device *idle_inject_register(struct cpumask *cpumask) | |
289 | { | |
290 | struct idle_inject_device *ii_dev; | |
291 | int cpu, cpu_rb; | |
292 | ||
293 | ii_dev = kzalloc(sizeof(*ii_dev) + cpumask_size(), GFP_KERNEL); | |
294 | if (!ii_dev) | |
295 | return NULL; | |
296 | ||
297 | cpumask_copy(to_cpumask(ii_dev->cpumask), cpumask); | |
298 | hrtimer_init(&ii_dev->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL); | |
299 | ii_dev->timer.function = idle_inject_timer_fn; | |
300 | ||
301 | for_each_cpu(cpu, to_cpumask(ii_dev->cpumask)) { | |
302 | ||
303 | if (per_cpu(idle_inject_device, cpu)) { | |
304 | pr_err("cpu%d is already registered\n", cpu); | |
305 | goto out_rollback; | |
306 | } | |
307 | ||
308 | per_cpu(idle_inject_device, cpu) = ii_dev; | |
309 | } | |
310 | ||
311 | return ii_dev; | |
312 | ||
313 | out_rollback: | |
314 | for_each_cpu(cpu_rb, to_cpumask(ii_dev->cpumask)) { | |
315 | if (cpu == cpu_rb) | |
316 | break; | |
317 | per_cpu(idle_inject_device, cpu_rb) = NULL; | |
318 | } | |
319 | ||
320 | kfree(ii_dev); | |
321 | ||
322 | return NULL; | |
323 | } | |
324 | ||
325 | /** | |
326 | * idle_inject_unregister - unregister idle injection control device | |
327 | * @ii_dev: idle injection control device to unregister | |
328 | * | |
329 | * The function stops idle injection for the given control device, | |
330 | * unregisters its kthreads and frees memory allocated when that device was | |
331 | * created. | |
332 | */ | |
333 | void idle_inject_unregister(struct idle_inject_device *ii_dev) | |
334 | { | |
335 | unsigned int cpu; | |
336 | ||
337 | idle_inject_stop(ii_dev); | |
338 | ||
339 | for_each_cpu(cpu, to_cpumask(ii_dev->cpumask)) | |
340 | per_cpu(idle_inject_device, cpu) = NULL; | |
341 | ||
342 | kfree(ii_dev); | |
343 | } | |
344 | ||
345 | static struct smp_hotplug_thread idle_inject_threads = { | |
346 | .store = &idle_inject_thread.tsk, | |
347 | .setup = idle_inject_setup, | |
348 | .thread_fn = idle_inject_fn, | |
349 | .thread_comm = "idle_inject/%u", | |
350 | .thread_should_run = idle_inject_should_run, | |
351 | }; | |
352 | ||
353 | static int __init idle_inject_init(void) | |
354 | { | |
355 | return smpboot_register_percpu_thread(&idle_inject_threads); | |
356 | } | |
357 | early_initcall(idle_inject_init); |