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
62 * @idle_duration_us: duration of CPU idle time to inject
63 * @run_duration_us: duration of CPU run time to allow
64 * @cpumask: mask of CPUs affected by idle injection
65 */
66 struct idle_inject_device {
67 struct hrtimer timer;
68 unsigned int idle_duration_us;
69 unsigned int run_duration_us;
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 {
107 unsigned int duration_us;
108 struct idle_inject_device *ii_dev =
109 container_of(timer, struct idle_inject_device, timer);
110
111 duration_us = READ_ONCE(ii_dev->run_duration_us);
112 duration_us += READ_ONCE(ii_dev->idle_duration_us);
113
114 idle_inject_wakeup(ii_dev);
115
116 hrtimer_forward_now(timer, ns_to_ktime(duration_us * NSEC_PER_USEC));
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
141 play_idle(READ_ONCE(ii_dev->idle_duration_us));
142 }
143
144 /**
145 * idle_inject_set_duration - idle and run duration update helper
146 * @run_duration_us: CPU run time to allow in microseconds
147 * @idle_duration_us: CPU idle time to inject in microseconds
148 */
149 void idle_inject_set_duration(struct idle_inject_device *ii_dev,
150 unsigned int run_duration_us,
151 unsigned int idle_duration_us)
152 {
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);
156 }
157 }
158
159 /**
160 * idle_inject_get_duration - idle and run duration retrieval helper
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
163 */
164 void idle_inject_get_duration(struct idle_inject_device *ii_dev,
165 unsigned int *run_duration_us,
166 unsigned int *idle_duration_us)
167 {
168 *run_duration_us = READ_ONCE(ii_dev->run_duration_us);
169 *idle_duration_us = READ_ONCE(ii_dev->idle_duration_us);
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 {
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);
186
187 if (!idle_duration_us || !run_duration_us)
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,
196 ns_to_ktime((idle_duration_us + run_duration_us) *
197 NSEC_PER_USEC),
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);