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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> | |
57 | #include <asm/atomic.h> | |
58 | ||
59 | static async_cookie_t next_cookie = 1; | |
60 | ||
61 | #define MAX_THREADS 256 | |
62 | #define MAX_WORK 32768 | |
63 | ||
64 | static LIST_HEAD(async_pending); | |
65 | static LIST_HEAD(async_running); | |
66 | static DEFINE_SPINLOCK(async_lock); | |
67 | ||
cdb80f63 AV |
68 | static int async_enabled = 0; |
69 | ||
22a9d645 AV |
70 | struct async_entry { |
71 | struct list_head list; | |
72 | async_cookie_t cookie; | |
73 | async_func_ptr *func; | |
74 | void *data; | |
75 | struct list_head *running; | |
76 | }; | |
77 | ||
78 | static DECLARE_WAIT_QUEUE_HEAD(async_done); | |
79 | static DECLARE_WAIT_QUEUE_HEAD(async_new); | |
80 | ||
81 | static atomic_t entry_count; | |
82 | static atomic_t thread_count; | |
83 | ||
84 | extern int initcall_debug; | |
85 | ||
86 | ||
87 | /* | |
88 | * MUST be called with the lock held! | |
89 | */ | |
90 | static async_cookie_t __lowest_in_progress(struct list_head *running) | |
91 | { | |
92 | struct async_entry *entry; | |
37a76bd4 AV |
93 | if (!list_empty(running)) { |
94 | entry = list_first_entry(running, | |
22a9d645 AV |
95 | struct async_entry, list); |
96 | return entry->cookie; | |
37a76bd4 AV |
97 | } else if (!list_empty(&async_pending)) { |
98 | entry = list_first_entry(&async_pending, | |
22a9d645 AV |
99 | struct async_entry, list); |
100 | return entry->cookie; | |
101 | } else { | |
102 | /* nothing in progress... next_cookie is "infinity" */ | |
103 | return next_cookie; | |
104 | } | |
105 | ||
106 | } | |
37a76bd4 AV |
107 | |
108 | static async_cookie_t lowest_in_progress(struct list_head *running) | |
109 | { | |
110 | unsigned long flags; | |
111 | async_cookie_t ret; | |
112 | ||
113 | spin_lock_irqsave(&async_lock, flags); | |
114 | ret = __lowest_in_progress(running); | |
115 | spin_unlock_irqrestore(&async_lock, flags); | |
116 | return ret; | |
117 | } | |
22a9d645 AV |
118 | /* |
119 | * pick the first pending entry and run it | |
120 | */ | |
121 | static void run_one_entry(void) | |
122 | { | |
123 | unsigned long flags; | |
124 | struct async_entry *entry; | |
125 | ktime_t calltime, delta, rettime; | |
126 | ||
127 | /* 1) pick one task from the pending queue */ | |
128 | ||
129 | spin_lock_irqsave(&async_lock, flags); | |
130 | if (list_empty(&async_pending)) | |
131 | goto out; | |
132 | entry = list_first_entry(&async_pending, struct async_entry, list); | |
133 | ||
134 | /* 2) move it to the running queue */ | |
135 | list_del(&entry->list); | |
136 | list_add_tail(&entry->list, &async_running); | |
137 | spin_unlock_irqrestore(&async_lock, flags); | |
138 | ||
139 | /* 3) run it (and print duration)*/ | |
ad160d23 | 140 | if (initcall_debug && system_state == SYSTEM_BOOTING) { |
22a9d645 AV |
141 | printk("calling %lli_%pF @ %i\n", entry->cookie, entry->func, task_pid_nr(current)); |
142 | calltime = ktime_get(); | |
143 | } | |
144 | entry->func(entry->data, entry->cookie); | |
ad160d23 | 145 | if (initcall_debug && system_state == SYSTEM_BOOTING) { |
22a9d645 AV |
146 | rettime = ktime_get(); |
147 | delta = ktime_sub(rettime, calltime); | |
148 | printk("initcall %lli_%pF returned 0 after %lld usecs\n", entry->cookie, | |
149 | entry->func, ktime_to_ns(delta) >> 10); | |
150 | } | |
151 | ||
152 | /* 4) remove it from the running queue */ | |
153 | spin_lock_irqsave(&async_lock, flags); | |
154 | list_del(&entry->list); | |
155 | ||
156 | /* 5) free the entry */ | |
157 | kfree(entry); | |
158 | atomic_dec(&entry_count); | |
159 | ||
160 | spin_unlock_irqrestore(&async_lock, flags); | |
161 | ||
162 | /* 6) wake up any waiters. */ | |
163 | wake_up(&async_done); | |
164 | return; | |
165 | ||
166 | out: | |
167 | spin_unlock_irqrestore(&async_lock, flags); | |
168 | } | |
169 | ||
170 | ||
171 | static async_cookie_t __async_schedule(async_func_ptr *ptr, void *data, struct list_head *running) | |
172 | { | |
173 | struct async_entry *entry; | |
174 | unsigned long flags; | |
175 | async_cookie_t newcookie; | |
176 | ||
177 | ||
178 | /* allow irq-off callers */ | |
179 | entry = kzalloc(sizeof(struct async_entry), GFP_ATOMIC); | |
180 | ||
181 | /* | |
182 | * If we're out of memory or if there's too much work | |
183 | * pending already, we execute synchronously. | |
184 | */ | |
cdb80f63 | 185 | if (!async_enabled || !entry || atomic_read(&entry_count) > MAX_WORK) { |
22a9d645 AV |
186 | kfree(entry); |
187 | spin_lock_irqsave(&async_lock, flags); | |
188 | newcookie = next_cookie++; | |
189 | spin_unlock_irqrestore(&async_lock, flags); | |
190 | ||
191 | /* low on memory.. run synchronously */ | |
192 | ptr(data, newcookie); | |
193 | return newcookie; | |
194 | } | |
195 | entry->func = ptr; | |
196 | entry->data = data; | |
197 | entry->running = running; | |
198 | ||
199 | spin_lock_irqsave(&async_lock, flags); | |
200 | newcookie = entry->cookie = next_cookie++; | |
201 | list_add_tail(&entry->list, &async_pending); | |
202 | atomic_inc(&entry_count); | |
203 | spin_unlock_irqrestore(&async_lock, flags); | |
204 | wake_up(&async_new); | |
205 | return newcookie; | |
206 | } | |
207 | ||
208 | async_cookie_t async_schedule(async_func_ptr *ptr, void *data) | |
209 | { | |
210 | return __async_schedule(ptr, data, &async_pending); | |
211 | } | |
212 | EXPORT_SYMBOL_GPL(async_schedule); | |
213 | ||
214 | async_cookie_t async_schedule_special(async_func_ptr *ptr, void *data, struct list_head *running) | |
215 | { | |
216 | return __async_schedule(ptr, data, running); | |
217 | } | |
218 | EXPORT_SYMBOL_GPL(async_schedule_special); | |
219 | ||
220 | void async_synchronize_full(void) | |
221 | { | |
33b04b93 AV |
222 | do { |
223 | async_synchronize_cookie(next_cookie); | |
224 | } while (!list_empty(&async_running) || !list_empty(&async_pending)); | |
22a9d645 AV |
225 | } |
226 | EXPORT_SYMBOL_GPL(async_synchronize_full); | |
227 | ||
228 | void async_synchronize_full_special(struct list_head *list) | |
229 | { | |
230 | async_synchronize_cookie_special(next_cookie, list); | |
231 | } | |
232 | EXPORT_SYMBOL_GPL(async_synchronize_full_special); | |
233 | ||
234 | void async_synchronize_cookie_special(async_cookie_t cookie, struct list_head *running) | |
235 | { | |
236 | ktime_t starttime, delta, endtime; | |
237 | ||
ad160d23 | 238 | if (initcall_debug && system_state == SYSTEM_BOOTING) { |
22a9d645 AV |
239 | printk("async_waiting @ %i\n", task_pid_nr(current)); |
240 | starttime = ktime_get(); | |
241 | } | |
242 | ||
37a76bd4 | 243 | wait_event(async_done, lowest_in_progress(running) >= cookie); |
22a9d645 | 244 | |
ad160d23 | 245 | if (initcall_debug && system_state == SYSTEM_BOOTING) { |
22a9d645 AV |
246 | endtime = ktime_get(); |
247 | delta = ktime_sub(endtime, starttime); | |
248 | ||
249 | printk("async_continuing @ %i after %lli usec\n", | |
250 | task_pid_nr(current), ktime_to_ns(delta) >> 10); | |
251 | } | |
252 | } | |
253 | EXPORT_SYMBOL_GPL(async_synchronize_cookie_special); | |
254 | ||
255 | void async_synchronize_cookie(async_cookie_t cookie) | |
256 | { | |
257 | async_synchronize_cookie_special(cookie, &async_running); | |
258 | } | |
259 | EXPORT_SYMBOL_GPL(async_synchronize_cookie); | |
260 | ||
261 | ||
262 | static int async_thread(void *unused) | |
263 | { | |
264 | DECLARE_WAITQUEUE(wq, current); | |
265 | add_wait_queue(&async_new, &wq); | |
266 | ||
267 | while (!kthread_should_stop()) { | |
268 | int ret = HZ; | |
269 | set_current_state(TASK_INTERRUPTIBLE); | |
270 | /* | |
271 | * check the list head without lock.. false positives | |
272 | * are dealt with inside run_one_entry() while holding | |
273 | * the lock. | |
274 | */ | |
275 | rmb(); | |
276 | if (!list_empty(&async_pending)) | |
277 | run_one_entry(); | |
278 | else | |
279 | ret = schedule_timeout(HZ); | |
280 | ||
281 | if (ret == 0) { | |
282 | /* | |
283 | * we timed out, this means we as thread are redundant. | |
284 | * we sign off and die, but we to avoid any races there | |
285 | * is a last-straw check to see if work snuck in. | |
286 | */ | |
287 | atomic_dec(&thread_count); | |
288 | wmb(); /* manager must see our departure first */ | |
289 | if (list_empty(&async_pending)) | |
290 | break; | |
291 | /* | |
292 | * woops work came in between us timing out and us | |
293 | * signing off; we need to stay alive and keep working. | |
294 | */ | |
295 | atomic_inc(&thread_count); | |
296 | } | |
297 | } | |
298 | remove_wait_queue(&async_new, &wq); | |
299 | ||
300 | return 0; | |
301 | } | |
302 | ||
303 | static int async_manager_thread(void *unused) | |
304 | { | |
305 | DECLARE_WAITQUEUE(wq, current); | |
306 | add_wait_queue(&async_new, &wq); | |
307 | ||
308 | while (!kthread_should_stop()) { | |
309 | int tc, ec; | |
310 | ||
311 | set_current_state(TASK_INTERRUPTIBLE); | |
312 | ||
313 | tc = atomic_read(&thread_count); | |
314 | rmb(); | |
315 | ec = atomic_read(&entry_count); | |
316 | ||
317 | while (tc < ec && tc < MAX_THREADS) { | |
318 | kthread_run(async_thread, NULL, "async/%i", tc); | |
319 | atomic_inc(&thread_count); | |
320 | tc++; | |
321 | } | |
322 | ||
323 | schedule(); | |
324 | } | |
325 | remove_wait_queue(&async_new, &wq); | |
326 | ||
327 | return 0; | |
328 | } | |
329 | ||
330 | static int __init async_init(void) | |
331 | { | |
cdb80f63 AV |
332 | if (async_enabled) |
333 | kthread_run(async_manager_thread, NULL, "async/mgr"); | |
22a9d645 AV |
334 | return 0; |
335 | } | |
336 | ||
cdb80f63 AV |
337 | static int __init setup_async(char *str) |
338 | { | |
339 | async_enabled = 1; | |
340 | return 1; | |
341 | } | |
342 | ||
343 | __setup("fastboot", setup_async); | |
344 | ||
345 | ||
22a9d645 | 346 | core_initcall(async_init); |