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