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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/bug.h> |
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> |
58 | #include <linux/delay.h> |
59 | #include <linux/slab.h> |
60 | #include <asm/atomic.h> |
61 | |
62 | static async_cookie_t next_cookie = 1; |
63 | |
64 | #define MAX_THREADS 256 |
65 | #define MAX_WORK 32768 |
66 | |
67 | static LIST_HEAD(async_pending); |
68 | static LIST_HEAD(async_running); |
69 | static DEFINE_SPINLOCK(async_lock); |
70 | |
71 | static int async_enabled = 0; |
72 | |
73 | struct async_entry { |
74 | struct list_head list; |
75 | async_cookie_t cookie; |
76 | async_func_ptr *func; |
77 | void *data; |
78 | struct list_head *running; |
79 | }; |
80 | |
81 | static DECLARE_WAIT_QUEUE_HEAD(async_done); |
82 | static DECLARE_WAIT_QUEUE_HEAD(async_new); |
83 | |
84 | static atomic_t entry_count; |
85 | static atomic_t thread_count; |
86 | |
87 | extern int initcall_debug; |
88 | |
89 | |
90 | /* |
91 | * MUST be called with the lock held! |
92 | */ |
93 | static async_cookie_t __lowest_in_progress(struct list_head *running) |
94 | { |
95 | struct async_entry *entry; |
96 | |
97 | if (!list_empty(running)) { |
98 | entry = list_first_entry(running, |
99 | struct async_entry, list); |
100 | return entry->cookie; |
101 | } |
102 | |
103 | list_for_each_entry(entry, &async_pending, list) |
104 | if (entry->running == running) |
105 | return entry->cookie; |
106 | |
107 | return next_cookie; /* "infinity" value */ |
108 | } |
109 | |
110 | static async_cookie_t lowest_in_progress(struct list_head *running) |
111 | { |
112 | unsigned long flags; |
113 | async_cookie_t ret; |
114 | |
115 | spin_lock_irqsave(&async_lock, flags); |
116 | ret = __lowest_in_progress(running); |
117 | spin_unlock_irqrestore(&async_lock, flags); |
118 | return ret; |
119 | } |
120 | /* |
121 | * pick the first pending entry and run it |
122 | */ |
123 | static void run_one_entry(void) |
124 | { |
125 | unsigned long flags; |
126 | struct async_entry *entry; |
127 | ktime_t calltime, delta, rettime; |
128 | |
129 | /* 1) pick one task from the pending queue */ |
130 | |
131 | spin_lock_irqsave(&async_lock, flags); |
132 | if (list_empty(&async_pending)) |
133 | goto out; |
134 | entry = list_first_entry(&async_pending, struct async_entry, list); |
135 | |
136 | /* 2) move it to the running queue */ |
137 | list_move_tail(&entry->list, entry->running); |
138 | spin_unlock_irqrestore(&async_lock, flags); |
139 | |
140 | /* 3) run it (and print duration)*/ |
141 | if (initcall_debug && system_state == SYSTEM_BOOTING) { |
142 | printk("calling %lli_%pF @ %i\n", (long long)entry->cookie, |
143 | entry->func, task_pid_nr(current)); |
144 | calltime = ktime_get(); |
145 | } |
146 | entry->func(entry->data, entry->cookie); |
147 | if (initcall_debug && system_state == SYSTEM_BOOTING) { |
148 | rettime = ktime_get(); |
149 | delta = ktime_sub(rettime, calltime); |
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); |
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 | */ |
189 | if (!async_enabled || !entry || atomic_read(&entry_count) > MAX_WORK) { |
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 | |
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 | */ |
220 | async_cookie_t async_schedule(async_func_ptr *ptr, void *data) |
221 | { |
222 | return __async_schedule(ptr, data, &async_running); |
223 | } |
224 | EXPORT_SYMBOL_GPL(async_schedule); |
225 | |
226 | /** |
227 | * async_schedule_domain - schedule a function for asynchronous execution within a certain domain |
228 | * @ptr: function to execute asynchronously |
229 | * @data: data pointer to pass to the function |
230 | * @running: running list for the domain |
231 | * |
232 | * Returns an async_cookie_t that may be used for checkpointing later. |
233 | * @running may be used in the async_synchronize_*_domain() functions |
234 | * to wait within a certain synchronization domain rather than globally. |
235 | * A synchronization domain is specified via the running queue @running to use. |
236 | * Note: This function may be called from atomic or non-atomic contexts. |
237 | */ |
238 | async_cookie_t async_schedule_domain(async_func_ptr *ptr, void *data, |
239 | struct list_head *running) |
240 | { |
241 | return __async_schedule(ptr, data, running); |
242 | } |
243 | EXPORT_SYMBOL_GPL(async_schedule_domain); |
244 | |
245 | /** |
246 | * async_synchronize_full - synchronize all asynchronous function calls |
247 | * |
248 | * This function waits until all asynchronous function calls have been done. |
249 | */ |
250 | void async_synchronize_full(void) |
251 | { |
252 | do { |
253 | async_synchronize_cookie(next_cookie); |
254 | } while (!list_empty(&async_running) || !list_empty(&async_pending)); |
255 | } |
256 | EXPORT_SYMBOL_GPL(async_synchronize_full); |
257 | |
258 | /** |
259 | * async_synchronize_full_domain - synchronize all asynchronous function within a certain domain |
260 | * @list: running list to synchronize on |
261 | * |
262 | * This function waits until all asynchronous function calls for the |
263 | * synchronization domain specified by the running list @list have been done. |
264 | */ |
265 | void async_synchronize_full_domain(struct list_head *list) |
266 | { |
267 | async_synchronize_cookie_domain(next_cookie, list); |
268 | } |
269 | EXPORT_SYMBOL_GPL(async_synchronize_full_domain); |
270 | |
271 | /** |
272 | * async_synchronize_cookie_domain - synchronize asynchronous function calls within a certain domain with cookie checkpointing |
273 | * @cookie: async_cookie_t to use as checkpoint |
274 | * @running: running list to synchronize on |
275 | * |
276 | * This function waits until all asynchronous function calls for the |
277 | * synchronization domain specified by the running list @list submitted |
278 | * prior to @cookie have been done. |
279 | */ |
280 | void async_synchronize_cookie_domain(async_cookie_t cookie, |
281 | struct list_head *running) |
282 | { |
283 | ktime_t starttime, delta, endtime; |
284 | |
285 | if (initcall_debug && system_state == SYSTEM_BOOTING) { |
286 | printk("async_waiting @ %i\n", task_pid_nr(current)); |
287 | starttime = ktime_get(); |
288 | } |
289 | |
290 | wait_event(async_done, lowest_in_progress(running) >= cookie); |
291 | |
292 | if (initcall_debug && system_state == SYSTEM_BOOTING) { |
293 | endtime = ktime_get(); |
294 | delta = ktime_sub(endtime, starttime); |
295 | |
296 | printk("async_continuing @ %i after %lli usec\n", |
297 | task_pid_nr(current), |
298 | (long long)ktime_to_ns(delta) >> 10); |
299 | } |
300 | } |
301 | EXPORT_SYMBOL_GPL(async_synchronize_cookie_domain); |
302 | |
303 | /** |
304 | * async_synchronize_cookie - synchronize asynchronous function calls with cookie checkpointing |
305 | * @cookie: async_cookie_t to use as checkpoint |
306 | * |
307 | * This function waits until all asynchronous function calls prior to @cookie |
308 | * have been done. |
309 | */ |
310 | void async_synchronize_cookie(async_cookie_t cookie) |
311 | { |
312 | async_synchronize_cookie_domain(cookie, &async_running); |
313 | } |
314 | EXPORT_SYMBOL_GPL(async_synchronize_cookie); |
315 | |
316 | |
317 | static int async_thread(void *unused) |
318 | { |
319 | DECLARE_WAITQUEUE(wq, current); |
320 | add_wait_queue(&async_new, &wq); |
321 | |
322 | while (!kthread_should_stop()) { |
323 | int ret = HZ; |
324 | set_current_state(TASK_INTERRUPTIBLE); |
325 | /* |
326 | * check the list head without lock.. false positives |
327 | * are dealt with inside run_one_entry() while holding |
328 | * the lock. |
329 | */ |
330 | rmb(); |
331 | if (!list_empty(&async_pending)) |
332 | run_one_entry(); |
333 | else |
334 | ret = schedule_timeout(HZ); |
335 | |
336 | if (ret == 0) { |
337 | /* |
338 | * we timed out, this means we as thread are redundant. |
339 | * we sign off and die, but we to avoid any races there |
340 | * is a last-straw check to see if work snuck in. |
341 | */ |
342 | atomic_dec(&thread_count); |
343 | wmb(); /* manager must see our departure first */ |
344 | if (list_empty(&async_pending)) |
345 | break; |
346 | /* |
347 | * woops work came in between us timing out and us |
348 | * signing off; we need to stay alive and keep working. |
349 | */ |
350 | atomic_inc(&thread_count); |
351 | } |
352 | } |
353 | remove_wait_queue(&async_new, &wq); |
354 | |
355 | return 0; |
356 | } |
357 | |
358 | static int async_manager_thread(void *unused) |
359 | { |
360 | DECLARE_WAITQUEUE(wq, current); |
361 | add_wait_queue(&async_new, &wq); |
362 | |
363 | while (!kthread_should_stop()) { |
364 | int tc, ec; |
365 | |
366 | set_current_state(TASK_INTERRUPTIBLE); |
367 | |
368 | tc = atomic_read(&thread_count); |
369 | rmb(); |
370 | ec = atomic_read(&entry_count); |
371 | |
372 | while (tc < ec && tc < MAX_THREADS) { |
373 | if (IS_ERR(kthread_run(async_thread, NULL, "async/%i", |
374 | tc))) { |
375 | msleep(100); |
376 | continue; |
377 | } |
378 | atomic_inc(&thread_count); |
379 | tc++; |
380 | } |
381 | |
382 | schedule(); |
383 | } |
384 | remove_wait_queue(&async_new, &wq); |
385 | |
386 | return 0; |
387 | } |
388 | |
389 | static int __init async_init(void) |
390 | { |
391 | async_enabled = |
392 | !IS_ERR(kthread_run(async_manager_thread, NULL, "async/mgr")); |
393 | |
394 | WARN_ON(!async_enabled); |
395 | return 0; |
396 | } |
397 | |
398 | core_initcall(async_init); |
399 |
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