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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> | |
97107943 | 52 | #include <linux/bug.h> |
22a9d645 AV |
53 | #include <linux/module.h> |
54 | #include <linux/wait.h> | |
55 | #include <linux/sched.h> | |
56 | #include <linux/init.h> | |
57 | #include <linux/kthread.h> | |
86532d8b | 58 | #include <linux/delay.h> |
22a9d645 AV |
59 | #include <asm/atomic.h> |
60 | ||
61 | static async_cookie_t next_cookie = 1; | |
62 | ||
63 | #define MAX_THREADS 256 | |
64 | #define MAX_WORK 32768 | |
65 | ||
66 | static LIST_HEAD(async_pending); | |
67 | static LIST_HEAD(async_running); | |
68 | static DEFINE_SPINLOCK(async_lock); | |
69 | ||
cdb80f63 AV |
70 | static int async_enabled = 0; |
71 | ||
22a9d645 AV |
72 | struct async_entry { |
73 | struct list_head list; | |
74 | async_cookie_t cookie; | |
75 | async_func_ptr *func; | |
76 | void *data; | |
77 | struct list_head *running; | |
78 | }; | |
79 | ||
80 | static DECLARE_WAIT_QUEUE_HEAD(async_done); | |
81 | static DECLARE_WAIT_QUEUE_HEAD(async_new); | |
82 | ||
83 | static atomic_t entry_count; | |
84 | static atomic_t thread_count; | |
85 | ||
86 | extern int initcall_debug; | |
87 | ||
88 | ||
89 | /* | |
90 | * MUST be called with the lock held! | |
91 | */ | |
92 | static async_cookie_t __lowest_in_progress(struct list_head *running) | |
93 | { | |
94 | struct async_entry *entry; | |
d5a877e8 JB |
95 | async_cookie_t ret = next_cookie; /* begin with "infinity" value */ |
96 | ||
37a76bd4 AV |
97 | if (!list_empty(running)) { |
98 | entry = list_first_entry(running, | |
22a9d645 | 99 | struct async_entry, list); |
d5a877e8 | 100 | ret = entry->cookie; |
22a9d645 AV |
101 | } |
102 | ||
d5a877e8 JB |
103 | if (!list_empty(&async_pending)) { |
104 | list_for_each_entry(entry, &async_pending, list) | |
105 | if (entry->running == running) { | |
106 | ret = entry->cookie; | |
107 | break; | |
108 | } | |
109 | } | |
110 | ||
111 | return ret; | |
22a9d645 | 112 | } |
37a76bd4 AV |
113 | |
114 | static async_cookie_t lowest_in_progress(struct list_head *running) | |
115 | { | |
116 | unsigned long flags; | |
117 | async_cookie_t ret; | |
118 | ||
119 | spin_lock_irqsave(&async_lock, flags); | |
120 | ret = __lowest_in_progress(running); | |
121 | spin_unlock_irqrestore(&async_lock, flags); | |
122 | return ret; | |
123 | } | |
22a9d645 AV |
124 | /* |
125 | * pick the first pending entry and run it | |
126 | */ | |
127 | static void run_one_entry(void) | |
128 | { | |
129 | unsigned long flags; | |
130 | struct async_entry *entry; | |
131 | ktime_t calltime, delta, rettime; | |
132 | ||
133 | /* 1) pick one task from the pending queue */ | |
134 | ||
135 | spin_lock_irqsave(&async_lock, flags); | |
136 | if (list_empty(&async_pending)) | |
137 | goto out; | |
138 | entry = list_first_entry(&async_pending, struct async_entry, list); | |
139 | ||
140 | /* 2) move it to the running queue */ | |
f7de7621 | 141 | list_move_tail(&entry->list, entry->running); |
22a9d645 AV |
142 | spin_unlock_irqrestore(&async_lock, flags); |
143 | ||
144 | /* 3) run it (and print duration)*/ | |
ad160d23 | 145 | if (initcall_debug && system_state == SYSTEM_BOOTING) { |
58763a29 AM |
146 | printk("calling %lli_%pF @ %i\n", (long long)entry->cookie, |
147 | entry->func, task_pid_nr(current)); | |
22a9d645 AV |
148 | calltime = ktime_get(); |
149 | } | |
150 | entry->func(entry->data, entry->cookie); | |
ad160d23 | 151 | if (initcall_debug && system_state == SYSTEM_BOOTING) { |
22a9d645 AV |
152 | rettime = ktime_get(); |
153 | delta = ktime_sub(rettime, calltime); | |
58763a29 AM |
154 | printk("initcall %lli_%pF returned 0 after %lld usecs\n", |
155 | (long long)entry->cookie, | |
156 | entry->func, | |
157 | (long long)ktime_to_ns(delta) >> 10); | |
22a9d645 AV |
158 | } |
159 | ||
160 | /* 4) remove it from the running queue */ | |
161 | spin_lock_irqsave(&async_lock, flags); | |
162 | list_del(&entry->list); | |
163 | ||
164 | /* 5) free the entry */ | |
165 | kfree(entry); | |
166 | atomic_dec(&entry_count); | |
167 | ||
168 | spin_unlock_irqrestore(&async_lock, flags); | |
169 | ||
170 | /* 6) wake up any waiters. */ | |
171 | wake_up(&async_done); | |
172 | return; | |
173 | ||
174 | out: | |
175 | spin_unlock_irqrestore(&async_lock, flags); | |
176 | } | |
177 | ||
178 | ||
179 | static async_cookie_t __async_schedule(async_func_ptr *ptr, void *data, struct list_head *running) | |
180 | { | |
181 | struct async_entry *entry; | |
182 | unsigned long flags; | |
183 | async_cookie_t newcookie; | |
184 | ||
185 | ||
186 | /* allow irq-off callers */ | |
187 | entry = kzalloc(sizeof(struct async_entry), GFP_ATOMIC); | |
188 | ||
189 | /* | |
190 | * If we're out of memory or if there's too much work | |
191 | * pending already, we execute synchronously. | |
192 | */ | |
cdb80f63 | 193 | if (!async_enabled || !entry || atomic_read(&entry_count) > MAX_WORK) { |
22a9d645 AV |
194 | kfree(entry); |
195 | spin_lock_irqsave(&async_lock, flags); | |
196 | newcookie = next_cookie++; | |
197 | spin_unlock_irqrestore(&async_lock, flags); | |
198 | ||
199 | /* low on memory.. run synchronously */ | |
200 | ptr(data, newcookie); | |
201 | return newcookie; | |
202 | } | |
203 | entry->func = ptr; | |
204 | entry->data = data; | |
205 | entry->running = running; | |
206 | ||
207 | spin_lock_irqsave(&async_lock, flags); | |
208 | newcookie = entry->cookie = next_cookie++; | |
209 | list_add_tail(&entry->list, &async_pending); | |
210 | atomic_inc(&entry_count); | |
211 | spin_unlock_irqrestore(&async_lock, flags); | |
212 | wake_up(&async_new); | |
213 | return newcookie; | |
214 | } | |
215 | ||
f30d5b30 CH |
216 | /** |
217 | * async_schedule - schedule a function for asynchronous execution | |
218 | * @ptr: function to execute asynchronously | |
219 | * @data: data pointer to pass to the function | |
220 | * | |
221 | * Returns an async_cookie_t that may be used for checkpointing later. | |
222 | * Note: This function may be called from atomic or non-atomic contexts. | |
223 | */ | |
22a9d645 AV |
224 | async_cookie_t async_schedule(async_func_ptr *ptr, void *data) |
225 | { | |
7a89bbc7 | 226 | return __async_schedule(ptr, data, &async_running); |
22a9d645 AV |
227 | } |
228 | EXPORT_SYMBOL_GPL(async_schedule); | |
229 | ||
f30d5b30 | 230 | /** |
766ccb9e | 231 | * async_schedule_domain - schedule a function for asynchronous execution within a certain domain |
f30d5b30 CH |
232 | * @ptr: function to execute asynchronously |
233 | * @data: data pointer to pass to the function | |
766ccb9e | 234 | * @running: running list for the domain |
f30d5b30 CH |
235 | * |
236 | * Returns an async_cookie_t that may be used for checkpointing later. | |
766ccb9e CH |
237 | * @running may be used in the async_synchronize_*_domain() functions |
238 | * to wait within a certain synchronization domain rather than globally. | |
239 | * A synchronization domain is specified via the running queue @running to use. | |
f30d5b30 CH |
240 | * Note: This function may be called from atomic or non-atomic contexts. |
241 | */ | |
766ccb9e CH |
242 | async_cookie_t async_schedule_domain(async_func_ptr *ptr, void *data, |
243 | struct list_head *running) | |
22a9d645 AV |
244 | { |
245 | return __async_schedule(ptr, data, running); | |
246 | } | |
766ccb9e | 247 | EXPORT_SYMBOL_GPL(async_schedule_domain); |
22a9d645 | 248 | |
f30d5b30 CH |
249 | /** |
250 | * async_synchronize_full - synchronize all asynchronous function calls | |
251 | * | |
252 | * This function waits until all asynchronous function calls have been done. | |
253 | */ | |
22a9d645 AV |
254 | void async_synchronize_full(void) |
255 | { | |
33b04b93 AV |
256 | do { |
257 | async_synchronize_cookie(next_cookie); | |
258 | } while (!list_empty(&async_running) || !list_empty(&async_pending)); | |
22a9d645 AV |
259 | } |
260 | EXPORT_SYMBOL_GPL(async_synchronize_full); | |
261 | ||
f30d5b30 | 262 | /** |
766ccb9e | 263 | * async_synchronize_full_domain - synchronize all asynchronous function within a certain domain |
f30d5b30 CH |
264 | * @list: running list to synchronize on |
265 | * | |
766ccb9e CH |
266 | * This function waits until all asynchronous function calls for the |
267 | * synchronization domain specified by the running list @list have been done. | |
f30d5b30 | 268 | */ |
766ccb9e | 269 | void async_synchronize_full_domain(struct list_head *list) |
22a9d645 | 270 | { |
766ccb9e | 271 | async_synchronize_cookie_domain(next_cookie, list); |
22a9d645 | 272 | } |
766ccb9e | 273 | EXPORT_SYMBOL_GPL(async_synchronize_full_domain); |
22a9d645 | 274 | |
f30d5b30 | 275 | /** |
766ccb9e | 276 | * async_synchronize_cookie_domain - synchronize asynchronous function calls within a certain domain with cookie checkpointing |
f30d5b30 CH |
277 | * @cookie: async_cookie_t to use as checkpoint |
278 | * @running: running list to synchronize on | |
279 | * | |
766ccb9e CH |
280 | * This function waits until all asynchronous function calls for the |
281 | * synchronization domain specified by the running list @list submitted | |
282 | * prior to @cookie have been done. | |
f30d5b30 | 283 | */ |
766ccb9e CH |
284 | void async_synchronize_cookie_domain(async_cookie_t cookie, |
285 | struct list_head *running) | |
22a9d645 AV |
286 | { |
287 | ktime_t starttime, delta, endtime; | |
288 | ||
ad160d23 | 289 | if (initcall_debug && system_state == SYSTEM_BOOTING) { |
22a9d645 AV |
290 | printk("async_waiting @ %i\n", task_pid_nr(current)); |
291 | starttime = ktime_get(); | |
292 | } | |
293 | ||
37a76bd4 | 294 | wait_event(async_done, lowest_in_progress(running) >= cookie); |
22a9d645 | 295 | |
ad160d23 | 296 | if (initcall_debug && system_state == SYSTEM_BOOTING) { |
22a9d645 AV |
297 | endtime = ktime_get(); |
298 | delta = ktime_sub(endtime, starttime); | |
299 | ||
300 | printk("async_continuing @ %i after %lli usec\n", | |
58763a29 AM |
301 | task_pid_nr(current), |
302 | (long long)ktime_to_ns(delta) >> 10); | |
22a9d645 AV |
303 | } |
304 | } | |
766ccb9e | 305 | EXPORT_SYMBOL_GPL(async_synchronize_cookie_domain); |
22a9d645 | 306 | |
f30d5b30 CH |
307 | /** |
308 | * async_synchronize_cookie - synchronize asynchronous function calls with cookie checkpointing | |
309 | * @cookie: async_cookie_t to use as checkpoint | |
310 | * | |
311 | * This function waits until all asynchronous function calls prior to @cookie | |
312 | * have been done. | |
313 | */ | |
22a9d645 AV |
314 | void async_synchronize_cookie(async_cookie_t cookie) |
315 | { | |
766ccb9e | 316 | async_synchronize_cookie_domain(cookie, &async_running); |
22a9d645 AV |
317 | } |
318 | EXPORT_SYMBOL_GPL(async_synchronize_cookie); | |
319 | ||
320 | ||
321 | static int async_thread(void *unused) | |
322 | { | |
323 | DECLARE_WAITQUEUE(wq, current); | |
324 | add_wait_queue(&async_new, &wq); | |
325 | ||
326 | while (!kthread_should_stop()) { | |
327 | int ret = HZ; | |
328 | set_current_state(TASK_INTERRUPTIBLE); | |
329 | /* | |
330 | * check the list head without lock.. false positives | |
331 | * are dealt with inside run_one_entry() while holding | |
332 | * the lock. | |
333 | */ | |
334 | rmb(); | |
335 | if (!list_empty(&async_pending)) | |
336 | run_one_entry(); | |
337 | else | |
338 | ret = schedule_timeout(HZ); | |
339 | ||
340 | if (ret == 0) { | |
341 | /* | |
342 | * we timed out, this means we as thread are redundant. | |
343 | * we sign off and die, but we to avoid any races there | |
344 | * is a last-straw check to see if work snuck in. | |
345 | */ | |
346 | atomic_dec(&thread_count); | |
347 | wmb(); /* manager must see our departure first */ | |
348 | if (list_empty(&async_pending)) | |
349 | break; | |
350 | /* | |
351 | * woops work came in between us timing out and us | |
352 | * signing off; we need to stay alive and keep working. | |
353 | */ | |
354 | atomic_inc(&thread_count); | |
355 | } | |
356 | } | |
357 | remove_wait_queue(&async_new, &wq); | |
358 | ||
359 | return 0; | |
360 | } | |
361 | ||
362 | static int async_manager_thread(void *unused) | |
363 | { | |
364 | DECLARE_WAITQUEUE(wq, current); | |
365 | add_wait_queue(&async_new, &wq); | |
366 | ||
367 | while (!kthread_should_stop()) { | |
368 | int tc, ec; | |
369 | ||
370 | set_current_state(TASK_INTERRUPTIBLE); | |
371 | ||
372 | tc = atomic_read(&thread_count); | |
373 | rmb(); | |
374 | ec = atomic_read(&entry_count); | |
375 | ||
376 | while (tc < ec && tc < MAX_THREADS) { | |
86532d8b CH |
377 | if (IS_ERR(kthread_run(async_thread, NULL, "async/%i", |
378 | tc))) { | |
379 | msleep(100); | |
380 | continue; | |
381 | } | |
22a9d645 AV |
382 | atomic_inc(&thread_count); |
383 | tc++; | |
384 | } | |
385 | ||
386 | schedule(); | |
387 | } | |
388 | remove_wait_queue(&async_new, &wq); | |
389 | ||
390 | return 0; | |
391 | } | |
392 | ||
393 | static int __init async_init(void) | |
394 | { | |
97107943 AV |
395 | async_enabled = |
396 | !IS_ERR(kthread_run(async_manager_thread, NULL, "async/mgr")); | |
22a9d645 | 397 | |
97107943 AV |
398 | WARN_ON(!async_enabled); |
399 | return 0; | |
cdb80f63 AV |
400 | } |
401 | ||
22a9d645 | 402 | core_initcall(async_init); |