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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 | * | |
0735069c YL |
22 | * The idle injection kthreads will call play_idle_precise() with the idle |
23 | * duration and max allowed latency specified as per the above. | |
88763a5c DL |
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> | |
00610935 | 46 | #include <linux/idle_inject.h> |
88763a5c DL |
47 | |
48 | #include <uapi/linux/sched/types.h> | |
49 | ||
50 | /** | |
51 | * struct idle_inject_thread - task on/off switch structure | |
52 | * @tsk: task injecting the idle cycles | |
53 | * @should_run: whether or not to run the task (for the smpboot kthread API) | |
54 | */ | |
55 | struct idle_inject_thread { | |
56 | struct task_struct *tsk; | |
57 | int should_run; | |
58 | }; | |
59 | ||
60 | /** | |
61 | * struct idle_inject_device - idle injection data | |
62 | * @timer: idle injection period timer | |
cd4c0763 DL |
63 | * @idle_duration_us: duration of CPU idle time to inject |
64 | * @run_duration_us: duration of CPU run time to allow | |
333cff6c | 65 | * @latency_us: max allowed latency |
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66 | * @cpumask: mask of CPUs affected by idle injection |
67 | */ | |
68 | struct idle_inject_device { | |
69 | struct hrtimer timer; | |
cd4c0763 DL |
70 | unsigned int idle_duration_us; |
71 | unsigned int run_duration_us; | |
333cff6c | 72 | unsigned int latency_us; |
27565c9e | 73 | unsigned long cpumask[]; |
88763a5c DL |
74 | }; |
75 | ||
76 | static DEFINE_PER_CPU(struct idle_inject_thread, idle_inject_thread); | |
77 | static DEFINE_PER_CPU(struct idle_inject_device *, idle_inject_device); | |
78 | ||
79 | /** | |
80 | * idle_inject_wakeup - Wake up idle injection threads | |
81 | * @ii_dev: target idle injection device | |
82 | * | |
83 | * Every idle injection task associated with the given idle injection device | |
84 | * and running on an online CPU will be woken up. | |
85 | */ | |
86 | static void idle_inject_wakeup(struct idle_inject_device *ii_dev) | |
87 | { | |
88 | struct idle_inject_thread *iit; | |
89 | unsigned int cpu; | |
90 | ||
91 | for_each_cpu_and(cpu, to_cpumask(ii_dev->cpumask), cpu_online_mask) { | |
92 | iit = per_cpu_ptr(&idle_inject_thread, cpu); | |
93 | iit->should_run = 1; | |
94 | wake_up_process(iit->tsk); | |
95 | } | |
96 | } | |
97 | ||
98 | /** | |
99 | * idle_inject_timer_fn - idle injection timer function | |
100 | * @timer: idle injection hrtimer | |
101 | * | |
102 | * This function is called when the idle injection timer expires. It wakes up | |
103 | * idle injection tasks associated with the timer and they, in turn, invoke | |
0735069c | 104 | * play_idle_precise() to inject a specified amount of CPU idle time. |
88763a5c DL |
105 | * |
106 | * Return: HRTIMER_RESTART. | |
107 | */ | |
108 | static enum hrtimer_restart idle_inject_timer_fn(struct hrtimer *timer) | |
109 | { | |
cd4c0763 | 110 | unsigned int duration_us; |
88763a5c DL |
111 | struct idle_inject_device *ii_dev = |
112 | container_of(timer, struct idle_inject_device, timer); | |
113 | ||
cd4c0763 DL |
114 | duration_us = READ_ONCE(ii_dev->run_duration_us); |
115 | duration_us += READ_ONCE(ii_dev->idle_duration_us); | |
88763a5c DL |
116 | |
117 | idle_inject_wakeup(ii_dev); | |
118 | ||
cd4c0763 | 119 | hrtimer_forward_now(timer, ns_to_ktime(duration_us * NSEC_PER_USEC)); |
88763a5c DL |
120 | |
121 | return HRTIMER_RESTART; | |
122 | } | |
123 | ||
124 | /** | |
125 | * idle_inject_fn - idle injection work function | |
126 | * @cpu: the CPU owning the task | |
127 | * | |
0735069c YL |
128 | * This function calls play_idle_precise() to inject a specified amount of CPU |
129 | * idle time. | |
88763a5c DL |
130 | */ |
131 | static void idle_inject_fn(unsigned int cpu) | |
132 | { | |
133 | struct idle_inject_device *ii_dev; | |
134 | struct idle_inject_thread *iit; | |
135 | ||
136 | ii_dev = per_cpu(idle_inject_device, cpu); | |
137 | iit = per_cpu_ptr(&idle_inject_thread, cpu); | |
138 | ||
139 | /* | |
140 | * Let the smpboot main loop know that the task should not run again. | |
141 | */ | |
142 | iit->should_run = 0; | |
143 | ||
333cff6c DL |
144 | play_idle_precise(READ_ONCE(ii_dev->idle_duration_us) * NSEC_PER_USEC, |
145 | READ_ONCE(ii_dev->latency_us) * NSEC_PER_USEC); | |
88763a5c DL |
146 | } |
147 | ||
148 | /** | |
149 | * idle_inject_set_duration - idle and run duration update helper | |
cd4c0763 DL |
150 | * @run_duration_us: CPU run time to allow in microseconds |
151 | * @idle_duration_us: CPU idle time to inject in microseconds | |
88763a5c DL |
152 | */ |
153 | void idle_inject_set_duration(struct idle_inject_device *ii_dev, | |
cd4c0763 DL |
154 | unsigned int run_duration_us, |
155 | unsigned int idle_duration_us) | |
88763a5c | 156 | { |
cd4c0763 DL |
157 | if (run_duration_us && idle_duration_us) { |
158 | WRITE_ONCE(ii_dev->run_duration_us, run_duration_us); | |
159 | WRITE_ONCE(ii_dev->idle_duration_us, idle_duration_us); | |
88763a5c DL |
160 | } |
161 | } | |
162 | ||
163 | /** | |
164 | * idle_inject_get_duration - idle and run duration retrieval helper | |
cd4c0763 DL |
165 | * @run_duration_us: memory location to store the current CPU run time |
166 | * @idle_duration_us: memory location to store the current CPU idle time | |
88763a5c DL |
167 | */ |
168 | void idle_inject_get_duration(struct idle_inject_device *ii_dev, | |
cd4c0763 DL |
169 | unsigned int *run_duration_us, |
170 | unsigned int *idle_duration_us) | |
88763a5c | 171 | { |
cd4c0763 DL |
172 | *run_duration_us = READ_ONCE(ii_dev->run_duration_us); |
173 | *idle_duration_us = READ_ONCE(ii_dev->idle_duration_us); | |
88763a5c DL |
174 | } |
175 | ||
333cff6c DL |
176 | /** |
177 | * idle_inject_set_latency - set the maximum latency allowed | |
178 | * @latency_us: set the latency requirement for the idle state | |
179 | */ | |
180 | void idle_inject_set_latency(struct idle_inject_device *ii_dev, | |
181 | unsigned int latency_us) | |
182 | { | |
183 | WRITE_ONCE(ii_dev->latency_us, latency_us); | |
184 | } | |
185 | ||
88763a5c DL |
186 | /** |
187 | * idle_inject_start - start idle injections | |
188 | * @ii_dev: idle injection control device structure | |
189 | * | |
190 | * The function starts idle injection by first waking up all of the idle | |
191 | * injection kthreads associated with @ii_dev to let them inject CPU idle time | |
192 | * sets up a timer to start the next idle injection period. | |
193 | * | |
194 | * Return: -EINVAL if the CPU idle or CPU run time is not set or 0 on success. | |
195 | */ | |
196 | int idle_inject_start(struct idle_inject_device *ii_dev) | |
197 | { | |
cd4c0763 DL |
198 | unsigned int idle_duration_us = READ_ONCE(ii_dev->idle_duration_us); |
199 | unsigned int run_duration_us = READ_ONCE(ii_dev->run_duration_us); | |
88763a5c | 200 | |
cd4c0763 | 201 | if (!idle_duration_us || !run_duration_us) |
88763a5c DL |
202 | return -EINVAL; |
203 | ||
204 | pr_debug("Starting injecting idle cycles on CPUs '%*pbl'\n", | |
205 | cpumask_pr_args(to_cpumask(ii_dev->cpumask))); | |
206 | ||
207 | idle_inject_wakeup(ii_dev); | |
208 | ||
209 | hrtimer_start(&ii_dev->timer, | |
cd4c0763 DL |
210 | ns_to_ktime((idle_duration_us + run_duration_us) * |
211 | NSEC_PER_USEC), | |
88763a5c DL |
212 | HRTIMER_MODE_REL); |
213 | ||
214 | return 0; | |
215 | } | |
216 | ||
217 | /** | |
218 | * idle_inject_stop - stops idle injections | |
219 | * @ii_dev: idle injection control device structure | |
220 | * | |
221 | * The function stops idle injection and waits for the threads to finish work. | |
222 | * If CPU idle time is being injected when this function runs, then it will | |
223 | * wait until the end of the cycle. | |
224 | * | |
225 | * When it returns, there is no more idle injection kthread activity. The | |
226 | * kthreads are scheduled out and the periodic timer is off. | |
227 | */ | |
228 | void idle_inject_stop(struct idle_inject_device *ii_dev) | |
229 | { | |
230 | struct idle_inject_thread *iit; | |
231 | unsigned int cpu; | |
232 | ||
233 | pr_debug("Stopping idle injection on CPUs '%*pbl'\n", | |
234 | cpumask_pr_args(to_cpumask(ii_dev->cpumask))); | |
235 | ||
236 | hrtimer_cancel(&ii_dev->timer); | |
237 | ||
238 | /* | |
239 | * Stopping idle injection requires all of the idle injection kthreads | |
240 | * associated with the given cpumask to be parked and stay that way, so | |
241 | * prevent CPUs from going online at this point. Any CPUs going online | |
242 | * after the loop below will be covered by clearing the should_run flag | |
243 | * that will cause the smpboot main loop to schedule them out. | |
244 | */ | |
245 | cpu_hotplug_disable(); | |
246 | ||
247 | /* | |
248 | * Iterate over all (online + offline) CPUs here in case one of them | |
249 | * goes offline with the should_run flag set so as to prevent its idle | |
250 | * injection kthread from running when the CPU goes online again after | |
251 | * the ii_dev has been freed. | |
252 | */ | |
253 | for_each_cpu(cpu, to_cpumask(ii_dev->cpumask)) { | |
254 | iit = per_cpu_ptr(&idle_inject_thread, cpu); | |
255 | iit->should_run = 0; | |
256 | ||
257 | wait_task_inactive(iit->tsk, 0); | |
258 | } | |
259 | ||
260 | cpu_hotplug_enable(); | |
261 | } | |
262 | ||
263 | /** | |
264 | * idle_inject_setup - prepare the current task for idle injection | |
265 | * @cpu: not used | |
266 | * | |
267 | * Called once, this function is in charge of setting the current task's | |
268 | * scheduler parameters to make it an RT task. | |
269 | */ | |
270 | static void idle_inject_setup(unsigned int cpu) | |
271 | { | |
c3f47cf9 | 272 | sched_set_fifo(current); |
88763a5c DL |
273 | } |
274 | ||
275 | /** | |
276 | * idle_inject_should_run - function helper for the smpboot API | |
277 | * @cpu: CPU the kthread is running on | |
278 | * | |
279 | * Return: whether or not the thread can run. | |
280 | */ | |
281 | static int idle_inject_should_run(unsigned int cpu) | |
282 | { | |
283 | struct idle_inject_thread *iit = | |
284 | per_cpu_ptr(&idle_inject_thread, cpu); | |
285 | ||
286 | return iit->should_run; | |
287 | } | |
288 | ||
289 | /** | |
290 | * idle_inject_register - initialize idle injection on a set of CPUs | |
291 | * @cpumask: CPUs to be affected by idle injection | |
292 | * | |
293 | * This function creates an idle injection control device structure for the | |
294 | * given set of CPUs and initializes the timer associated with it. It does not | |
295 | * start any injection cycles. | |
296 | * | |
297 | * Return: NULL if memory allocation fails, idle injection control device | |
298 | * pointer on success. | |
299 | */ | |
300 | struct idle_inject_device *idle_inject_register(struct cpumask *cpumask) | |
301 | { | |
302 | struct idle_inject_device *ii_dev; | |
303 | int cpu, cpu_rb; | |
304 | ||
305 | ii_dev = kzalloc(sizeof(*ii_dev) + cpumask_size(), GFP_KERNEL); | |
306 | if (!ii_dev) | |
307 | return NULL; | |
308 | ||
309 | cpumask_copy(to_cpumask(ii_dev->cpumask), cpumask); | |
310 | hrtimer_init(&ii_dev->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL); | |
311 | ii_dev->timer.function = idle_inject_timer_fn; | |
333cff6c | 312 | ii_dev->latency_us = UINT_MAX; |
88763a5c DL |
313 | |
314 | for_each_cpu(cpu, to_cpumask(ii_dev->cpumask)) { | |
315 | ||
316 | if (per_cpu(idle_inject_device, cpu)) { | |
317 | pr_err("cpu%d is already registered\n", cpu); | |
318 | goto out_rollback; | |
319 | } | |
320 | ||
321 | per_cpu(idle_inject_device, cpu) = ii_dev; | |
322 | } | |
323 | ||
324 | return ii_dev; | |
325 | ||
326 | out_rollback: | |
327 | for_each_cpu(cpu_rb, to_cpumask(ii_dev->cpumask)) { | |
328 | if (cpu == cpu_rb) | |
329 | break; | |
330 | per_cpu(idle_inject_device, cpu_rb) = NULL; | |
331 | } | |
332 | ||
333 | kfree(ii_dev); | |
334 | ||
335 | return NULL; | |
336 | } | |
337 | ||
338 | /** | |
339 | * idle_inject_unregister - unregister idle injection control device | |
340 | * @ii_dev: idle injection control device to unregister | |
341 | * | |
342 | * The function stops idle injection for the given control device, | |
343 | * unregisters its kthreads and frees memory allocated when that device was | |
344 | * created. | |
345 | */ | |
346 | void idle_inject_unregister(struct idle_inject_device *ii_dev) | |
347 | { | |
348 | unsigned int cpu; | |
349 | ||
350 | idle_inject_stop(ii_dev); | |
351 | ||
352 | for_each_cpu(cpu, to_cpumask(ii_dev->cpumask)) | |
353 | per_cpu(idle_inject_device, cpu) = NULL; | |
354 | ||
355 | kfree(ii_dev); | |
356 | } | |
357 | ||
358 | static struct smp_hotplug_thread idle_inject_threads = { | |
359 | .store = &idle_inject_thread.tsk, | |
360 | .setup = idle_inject_setup, | |
361 | .thread_fn = idle_inject_fn, | |
362 | .thread_comm = "idle_inject/%u", | |
363 | .thread_should_run = idle_inject_should_run, | |
364 | }; | |
365 | ||
366 | static int __init idle_inject_init(void) | |
367 | { | |
368 | return smpboot_register_percpu_thread(&idle_inject_threads); | |
369 | } | |
370 | early_initcall(idle_inject_init); |