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22a9d645 AV |
1 | /* |
2 | * async.c: Asynchronous function calls for boot performance | |
3 | * | |
4 | * (C) Copyright 2009 Intel Corporation | |
5 | * Author: Arjan van de Ven <arjan@linux.intel.com> | |
6 | * | |
7 | * This program is free software; you can redistribute it and/or | |
8 | * modify it under the terms of the GNU General Public License | |
9 | * as published by the Free Software Foundation; version 2 | |
10 | * of the License. | |
11 | */ | |
12 | ||
13 | ||
14 | /* | |
15 | ||
16 | Goals and Theory of Operation | |
17 | ||
18 | The primary goal of this feature is to reduce the kernel boot time, | |
19 | by doing various independent hardware delays and discovery operations | |
20 | decoupled and not strictly serialized. | |
21 | ||
22 | More specifically, the asynchronous function call concept allows | |
23 | certain operations (primarily during system boot) to happen | |
24 | asynchronously, out of order, while these operations still | |
25 | have their externally visible parts happen sequentially and in-order. | |
26 | (not unlike how out-of-order CPUs retire their instructions in order) | |
27 | ||
28 | Key to the asynchronous function call implementation is the concept of | |
29 | a "sequence cookie" (which, although it has an abstracted type, can be | |
30 | thought of as a monotonically incrementing number). | |
31 | ||
32 | The async core will assign each scheduled event such a sequence cookie and | |
33 | pass this to the called functions. | |
34 | ||
35 | The asynchronously called function should before doing a globally visible | |
36 | operation, such as registering device numbers, call the | |
37 | async_synchronize_cookie() function and pass in its own cookie. The | |
38 | async_synchronize_cookie() function will make sure that all asynchronous | |
39 | operations that were scheduled prior to the operation corresponding with the | |
40 | cookie have completed. | |
41 | ||
42 | Subsystem/driver initialization code that scheduled asynchronous probe | |
43 | functions, but which shares global resources with other drivers/subsystems | |
44 | that do not use the asynchronous call feature, need to do a full | |
45 | synchronization with the async_synchronize_full() function, before returning | |
46 | from their init function. This is to maintain strict ordering between the | |
47 | asynchronous and synchronous parts of the kernel. | |
48 | ||
49 | */ | |
50 | ||
51 | #include <linux/async.h> | |
52 | #include <linux/module.h> | |
53 | #include <linux/wait.h> | |
54 | #include <linux/sched.h> | |
55 | #include <linux/init.h> | |
56 | #include <linux/kthread.h> | |
86532d8b | 57 | #include <linux/delay.h> |
22a9d645 AV |
58 | #include <asm/atomic.h> |
59 | ||
60 | static async_cookie_t next_cookie = 1; | |
61 | ||
62 | #define MAX_THREADS 256 | |
63 | #define MAX_WORK 32768 | |
64 | ||
65 | static LIST_HEAD(async_pending); | |
66 | static LIST_HEAD(async_running); | |
67 | static DEFINE_SPINLOCK(async_lock); | |
68 | ||
cdb80f63 AV |
69 | static int async_enabled = 0; |
70 | ||
22a9d645 AV |
71 | struct async_entry { |
72 | struct list_head list; | |
73 | async_cookie_t cookie; | |
74 | async_func_ptr *func; | |
75 | void *data; | |
76 | struct list_head *running; | |
77 | }; | |
78 | ||
79 | static DECLARE_WAIT_QUEUE_HEAD(async_done); | |
80 | static DECLARE_WAIT_QUEUE_HEAD(async_new); | |
81 | ||
82 | static atomic_t entry_count; | |
83 | static atomic_t thread_count; | |
84 | ||
85 | extern int initcall_debug; | |
86 | ||
87 | ||
88 | /* | |
89 | * MUST be called with the lock held! | |
90 | */ | |
91 | static async_cookie_t __lowest_in_progress(struct list_head *running) | |
92 | { | |
93 | struct async_entry *entry; | |
37a76bd4 AV |
94 | if (!list_empty(running)) { |
95 | entry = list_first_entry(running, | |
22a9d645 AV |
96 | struct async_entry, list); |
97 | return entry->cookie; | |
37a76bd4 AV |
98 | } else if (!list_empty(&async_pending)) { |
99 | entry = list_first_entry(&async_pending, | |
22a9d645 AV |
100 | struct async_entry, list); |
101 | return entry->cookie; | |
102 | } else { | |
103 | /* nothing in progress... next_cookie is "infinity" */ | |
104 | return next_cookie; | |
105 | } | |
106 | ||
107 | } | |
37a76bd4 AV |
108 | |
109 | static async_cookie_t lowest_in_progress(struct list_head *running) | |
110 | { | |
111 | unsigned long flags; | |
112 | async_cookie_t ret; | |
113 | ||
114 | spin_lock_irqsave(&async_lock, flags); | |
115 | ret = __lowest_in_progress(running); | |
116 | spin_unlock_irqrestore(&async_lock, flags); | |
117 | return ret; | |
118 | } | |
22a9d645 AV |
119 | /* |
120 | * pick the first pending entry and run it | |
121 | */ | |
122 | static void run_one_entry(void) | |
123 | { | |
124 | unsigned long flags; | |
125 | struct async_entry *entry; | |
126 | ktime_t calltime, delta, rettime; | |
127 | ||
128 | /* 1) pick one task from the pending queue */ | |
129 | ||
130 | spin_lock_irqsave(&async_lock, flags); | |
131 | if (list_empty(&async_pending)) | |
132 | goto out; | |
133 | entry = list_first_entry(&async_pending, struct async_entry, list); | |
134 | ||
135 | /* 2) move it to the running queue */ | |
136 | list_del(&entry->list); | |
7a89bbc7 | 137 | list_add_tail(&entry->list, entry->running); |
22a9d645 AV |
138 | spin_unlock_irqrestore(&async_lock, flags); |
139 | ||
140 | /* 3) run it (and print duration)*/ | |
ad160d23 | 141 | if (initcall_debug && system_state == SYSTEM_BOOTING) { |
58763a29 AM |
142 | printk("calling %lli_%pF @ %i\n", (long long)entry->cookie, |
143 | entry->func, task_pid_nr(current)); | |
22a9d645 AV |
144 | calltime = ktime_get(); |
145 | } | |
146 | entry->func(entry->data, entry->cookie); | |
ad160d23 | 147 | if (initcall_debug && system_state == SYSTEM_BOOTING) { |
22a9d645 AV |
148 | rettime = ktime_get(); |
149 | delta = ktime_sub(rettime, calltime); | |
58763a29 AM |
150 | printk("initcall %lli_%pF returned 0 after %lld usecs\n", |
151 | (long long)entry->cookie, | |
152 | entry->func, | |
153 | (long long)ktime_to_ns(delta) >> 10); | |
22a9d645 AV |
154 | } |
155 | ||
156 | /* 4) remove it from the running queue */ | |
157 | spin_lock_irqsave(&async_lock, flags); | |
158 | list_del(&entry->list); | |
159 | ||
160 | /* 5) free the entry */ | |
161 | kfree(entry); | |
162 | atomic_dec(&entry_count); | |
163 | ||
164 | spin_unlock_irqrestore(&async_lock, flags); | |
165 | ||
166 | /* 6) wake up any waiters. */ | |
167 | wake_up(&async_done); | |
168 | return; | |
169 | ||
170 | out: | |
171 | spin_unlock_irqrestore(&async_lock, flags); | |
172 | } | |
173 | ||
174 | ||
175 | static async_cookie_t __async_schedule(async_func_ptr *ptr, void *data, struct list_head *running) | |
176 | { | |
177 | struct async_entry *entry; | |
178 | unsigned long flags; | |
179 | async_cookie_t newcookie; | |
180 | ||
181 | ||
182 | /* allow irq-off callers */ | |
183 | entry = kzalloc(sizeof(struct async_entry), GFP_ATOMIC); | |
184 | ||
185 | /* | |
186 | * If we're out of memory or if there's too much work | |
187 | * pending already, we execute synchronously. | |
188 | */ | |
cdb80f63 | 189 | if (!async_enabled || !entry || atomic_read(&entry_count) > MAX_WORK) { |
22a9d645 AV |
190 | kfree(entry); |
191 | spin_lock_irqsave(&async_lock, flags); | |
192 | newcookie = next_cookie++; | |
193 | spin_unlock_irqrestore(&async_lock, flags); | |
194 | ||
195 | /* low on memory.. run synchronously */ | |
196 | ptr(data, newcookie); | |
197 | return newcookie; | |
198 | } | |
199 | entry->func = ptr; | |
200 | entry->data = data; | |
201 | entry->running = running; | |
202 | ||
203 | spin_lock_irqsave(&async_lock, flags); | |
204 | newcookie = entry->cookie = next_cookie++; | |
205 | list_add_tail(&entry->list, &async_pending); | |
206 | atomic_inc(&entry_count); | |
207 | spin_unlock_irqrestore(&async_lock, flags); | |
208 | wake_up(&async_new); | |
209 | return newcookie; | |
210 | } | |
211 | ||
f30d5b30 CH |
212 | /** |
213 | * async_schedule - schedule a function for asynchronous execution | |
214 | * @ptr: function to execute asynchronously | |
215 | * @data: data pointer to pass to the function | |
216 | * | |
217 | * Returns an async_cookie_t that may be used for checkpointing later. | |
218 | * Note: This function may be called from atomic or non-atomic contexts. | |
219 | */ | |
22a9d645 AV |
220 | async_cookie_t async_schedule(async_func_ptr *ptr, void *data) |
221 | { | |
7a89bbc7 | 222 | return __async_schedule(ptr, data, &async_running); |
22a9d645 AV |
223 | } |
224 | EXPORT_SYMBOL_GPL(async_schedule); | |
225 | ||
f30d5b30 CH |
226 | /** |
227 | * async_schedule_special - schedule a function for asynchronous execution with a special running queue | |
228 | * @ptr: function to execute asynchronously | |
229 | * @data: data pointer to pass to the function | |
230 | * @running: list head to add to while running | |
231 | * | |
232 | * Returns an async_cookie_t that may be used for checkpointing later. | |
233 | * @running may be used in the async_synchronize_*_special() functions | |
234 | * to wait on a special running queue rather than on the global running | |
235 | * queue. | |
236 | * Note: This function may be called from atomic or non-atomic contexts. | |
237 | */ | |
22a9d645 AV |
238 | async_cookie_t async_schedule_special(async_func_ptr *ptr, void *data, struct list_head *running) |
239 | { | |
240 | return __async_schedule(ptr, data, running); | |
241 | } | |
242 | EXPORT_SYMBOL_GPL(async_schedule_special); | |
243 | ||
f30d5b30 CH |
244 | /** |
245 | * async_synchronize_full - synchronize all asynchronous function calls | |
246 | * | |
247 | * This function waits until all asynchronous function calls have been done. | |
248 | */ | |
22a9d645 AV |
249 | void async_synchronize_full(void) |
250 | { | |
33b04b93 AV |
251 | do { |
252 | async_synchronize_cookie(next_cookie); | |
253 | } while (!list_empty(&async_running) || !list_empty(&async_pending)); | |
22a9d645 AV |
254 | } |
255 | EXPORT_SYMBOL_GPL(async_synchronize_full); | |
256 | ||
f30d5b30 CH |
257 | /** |
258 | * async_synchronize_full_special - synchronize all asynchronous function calls for a running list | |
259 | * @list: running list to synchronize on | |
260 | * | |
261 | * This function waits until all asynchronous function calls for the running | |
262 | * list @list have been done. | |
263 | */ | |
22a9d645 AV |
264 | void async_synchronize_full_special(struct list_head *list) |
265 | { | |
266 | async_synchronize_cookie_special(next_cookie, list); | |
267 | } | |
268 | EXPORT_SYMBOL_GPL(async_synchronize_full_special); | |
269 | ||
f30d5b30 CH |
270 | /** |
271 | * async_synchronize_cookie_special - synchronize asynchronous function calls on a running list with cookie checkpointing | |
272 | * @cookie: async_cookie_t to use as checkpoint | |
273 | * @running: running list to synchronize on | |
274 | * | |
275 | * This function waits until all asynchronous function calls for the running | |
276 | * list @list submitted prior to @cookie have been done. | |
277 | */ | |
22a9d645 AV |
278 | void async_synchronize_cookie_special(async_cookie_t cookie, struct list_head *running) |
279 | { | |
280 | ktime_t starttime, delta, endtime; | |
281 | ||
ad160d23 | 282 | if (initcall_debug && system_state == SYSTEM_BOOTING) { |
22a9d645 AV |
283 | printk("async_waiting @ %i\n", task_pid_nr(current)); |
284 | starttime = ktime_get(); | |
285 | } | |
286 | ||
37a76bd4 | 287 | wait_event(async_done, lowest_in_progress(running) >= cookie); |
22a9d645 | 288 | |
ad160d23 | 289 | if (initcall_debug && system_state == SYSTEM_BOOTING) { |
22a9d645 AV |
290 | endtime = ktime_get(); |
291 | delta = ktime_sub(endtime, starttime); | |
292 | ||
293 | printk("async_continuing @ %i after %lli usec\n", | |
58763a29 AM |
294 | task_pid_nr(current), |
295 | (long long)ktime_to_ns(delta) >> 10); | |
22a9d645 AV |
296 | } |
297 | } | |
298 | EXPORT_SYMBOL_GPL(async_synchronize_cookie_special); | |
299 | ||
f30d5b30 CH |
300 | /** |
301 | * async_synchronize_cookie - synchronize asynchronous function calls with cookie checkpointing | |
302 | * @cookie: async_cookie_t to use as checkpoint | |
303 | * | |
304 | * This function waits until all asynchronous function calls prior to @cookie | |
305 | * have been done. | |
306 | */ | |
22a9d645 AV |
307 | void async_synchronize_cookie(async_cookie_t cookie) |
308 | { | |
309 | async_synchronize_cookie_special(cookie, &async_running); | |
310 | } | |
311 | EXPORT_SYMBOL_GPL(async_synchronize_cookie); | |
312 | ||
313 | ||
314 | static int async_thread(void *unused) | |
315 | { | |
316 | DECLARE_WAITQUEUE(wq, current); | |
317 | add_wait_queue(&async_new, &wq); | |
318 | ||
319 | while (!kthread_should_stop()) { | |
320 | int ret = HZ; | |
321 | set_current_state(TASK_INTERRUPTIBLE); | |
322 | /* | |
323 | * check the list head without lock.. false positives | |
324 | * are dealt with inside run_one_entry() while holding | |
325 | * the lock. | |
326 | */ | |
327 | rmb(); | |
328 | if (!list_empty(&async_pending)) | |
329 | run_one_entry(); | |
330 | else | |
331 | ret = schedule_timeout(HZ); | |
332 | ||
333 | if (ret == 0) { | |
334 | /* | |
335 | * we timed out, this means we as thread are redundant. | |
336 | * we sign off and die, but we to avoid any races there | |
337 | * is a last-straw check to see if work snuck in. | |
338 | */ | |
339 | atomic_dec(&thread_count); | |
340 | wmb(); /* manager must see our departure first */ | |
341 | if (list_empty(&async_pending)) | |
342 | break; | |
343 | /* | |
344 | * woops work came in between us timing out and us | |
345 | * signing off; we need to stay alive and keep working. | |
346 | */ | |
347 | atomic_inc(&thread_count); | |
348 | } | |
349 | } | |
350 | remove_wait_queue(&async_new, &wq); | |
351 | ||
352 | return 0; | |
353 | } | |
354 | ||
355 | static int async_manager_thread(void *unused) | |
356 | { | |
357 | DECLARE_WAITQUEUE(wq, current); | |
358 | add_wait_queue(&async_new, &wq); | |
359 | ||
360 | while (!kthread_should_stop()) { | |
361 | int tc, ec; | |
362 | ||
363 | set_current_state(TASK_INTERRUPTIBLE); | |
364 | ||
365 | tc = atomic_read(&thread_count); | |
366 | rmb(); | |
367 | ec = atomic_read(&entry_count); | |
368 | ||
369 | while (tc < ec && tc < MAX_THREADS) { | |
86532d8b CH |
370 | if (IS_ERR(kthread_run(async_thread, NULL, "async/%i", |
371 | tc))) { | |
372 | msleep(100); | |
373 | continue; | |
374 | } | |
22a9d645 AV |
375 | atomic_inc(&thread_count); |
376 | tc++; | |
377 | } | |
378 | ||
379 | schedule(); | |
380 | } | |
381 | remove_wait_queue(&async_new, &wq); | |
382 | ||
383 | return 0; | |
384 | } | |
385 | ||
386 | static int __init async_init(void) | |
387 | { | |
cdb80f63 | 388 | if (async_enabled) |
86532d8b CH |
389 | if (IS_ERR(kthread_run(async_manager_thread, NULL, |
390 | "async/mgr"))) | |
391 | async_enabled = 0; | |
22a9d645 AV |
392 | return 0; |
393 | } | |
394 | ||
cdb80f63 AV |
395 | static int __init setup_async(char *str) |
396 | { | |
397 | async_enabled = 1; | |
398 | return 1; | |
399 | } | |
400 | ||
401 | __setup("fastboot", setup_async); | |
402 | ||
403 | ||
22a9d645 | 404 | core_initcall(async_init); |