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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; | |
93 | if (!list_empty(&async_pending)) { | |
94 | entry = list_first_entry(&async_pending, | |
95 | struct async_entry, list); | |
96 | return entry->cookie; | |
97 | } else if (!list_empty(running)) { | |
98 | entry = list_first_entry(running, | |
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 | } | |
107 | /* | |
108 | * pick the first pending entry and run it | |
109 | */ | |
110 | static void run_one_entry(void) | |
111 | { | |
112 | unsigned long flags; | |
113 | struct async_entry *entry; | |
114 | ktime_t calltime, delta, rettime; | |
115 | ||
116 | /* 1) pick one task from the pending queue */ | |
117 | ||
118 | spin_lock_irqsave(&async_lock, flags); | |
119 | if (list_empty(&async_pending)) | |
120 | goto out; | |
121 | entry = list_first_entry(&async_pending, struct async_entry, list); | |
122 | ||
123 | /* 2) move it to the running queue */ | |
124 | list_del(&entry->list); | |
125 | list_add_tail(&entry->list, &async_running); | |
126 | spin_unlock_irqrestore(&async_lock, flags); | |
127 | ||
128 | /* 3) run it (and print duration)*/ | |
ad160d23 | 129 | if (initcall_debug && system_state == SYSTEM_BOOTING) { |
22a9d645 AV |
130 | printk("calling %lli_%pF @ %i\n", entry->cookie, entry->func, task_pid_nr(current)); |
131 | calltime = ktime_get(); | |
132 | } | |
133 | entry->func(entry->data, entry->cookie); | |
ad160d23 | 134 | if (initcall_debug && system_state == SYSTEM_BOOTING) { |
22a9d645 AV |
135 | rettime = ktime_get(); |
136 | delta = ktime_sub(rettime, calltime); | |
137 | printk("initcall %lli_%pF returned 0 after %lld usecs\n", entry->cookie, | |
138 | entry->func, ktime_to_ns(delta) >> 10); | |
139 | } | |
140 | ||
141 | /* 4) remove it from the running queue */ | |
142 | spin_lock_irqsave(&async_lock, flags); | |
143 | list_del(&entry->list); | |
144 | ||
145 | /* 5) free the entry */ | |
146 | kfree(entry); | |
147 | atomic_dec(&entry_count); | |
148 | ||
149 | spin_unlock_irqrestore(&async_lock, flags); | |
150 | ||
151 | /* 6) wake up any waiters. */ | |
152 | wake_up(&async_done); | |
153 | return; | |
154 | ||
155 | out: | |
156 | spin_unlock_irqrestore(&async_lock, flags); | |
157 | } | |
158 | ||
159 | ||
160 | static async_cookie_t __async_schedule(async_func_ptr *ptr, void *data, struct list_head *running) | |
161 | { | |
162 | struct async_entry *entry; | |
163 | unsigned long flags; | |
164 | async_cookie_t newcookie; | |
165 | ||
166 | ||
167 | /* allow irq-off callers */ | |
168 | entry = kzalloc(sizeof(struct async_entry), GFP_ATOMIC); | |
169 | ||
170 | /* | |
171 | * If we're out of memory or if there's too much work | |
172 | * pending already, we execute synchronously. | |
173 | */ | |
cdb80f63 | 174 | if (!async_enabled || !entry || atomic_read(&entry_count) > MAX_WORK) { |
22a9d645 AV |
175 | kfree(entry); |
176 | spin_lock_irqsave(&async_lock, flags); | |
177 | newcookie = next_cookie++; | |
178 | spin_unlock_irqrestore(&async_lock, flags); | |
179 | ||
180 | /* low on memory.. run synchronously */ | |
181 | ptr(data, newcookie); | |
182 | return newcookie; | |
183 | } | |
184 | entry->func = ptr; | |
185 | entry->data = data; | |
186 | entry->running = running; | |
187 | ||
188 | spin_lock_irqsave(&async_lock, flags); | |
189 | newcookie = entry->cookie = next_cookie++; | |
190 | list_add_tail(&entry->list, &async_pending); | |
191 | atomic_inc(&entry_count); | |
192 | spin_unlock_irqrestore(&async_lock, flags); | |
193 | wake_up(&async_new); | |
194 | return newcookie; | |
195 | } | |
196 | ||
197 | async_cookie_t async_schedule(async_func_ptr *ptr, void *data) | |
198 | { | |
199 | return __async_schedule(ptr, data, &async_pending); | |
200 | } | |
201 | EXPORT_SYMBOL_GPL(async_schedule); | |
202 | ||
203 | async_cookie_t async_schedule_special(async_func_ptr *ptr, void *data, struct list_head *running) | |
204 | { | |
205 | return __async_schedule(ptr, data, running); | |
206 | } | |
207 | EXPORT_SYMBOL_GPL(async_schedule_special); | |
208 | ||
209 | void async_synchronize_full(void) | |
210 | { | |
33b04b93 AV |
211 | do { |
212 | async_synchronize_cookie(next_cookie); | |
213 | } while (!list_empty(&async_running) || !list_empty(&async_pending)); | |
22a9d645 AV |
214 | } |
215 | EXPORT_SYMBOL_GPL(async_synchronize_full); | |
216 | ||
217 | void async_synchronize_full_special(struct list_head *list) | |
218 | { | |
219 | async_synchronize_cookie_special(next_cookie, list); | |
220 | } | |
221 | EXPORT_SYMBOL_GPL(async_synchronize_full_special); | |
222 | ||
223 | void async_synchronize_cookie_special(async_cookie_t cookie, struct list_head *running) | |
224 | { | |
225 | ktime_t starttime, delta, endtime; | |
226 | ||
ad160d23 | 227 | if (initcall_debug && system_state == SYSTEM_BOOTING) { |
22a9d645 AV |
228 | printk("async_waiting @ %i\n", task_pid_nr(current)); |
229 | starttime = ktime_get(); | |
230 | } | |
231 | ||
232 | wait_event(async_done, __lowest_in_progress(running) >= cookie); | |
233 | ||
ad160d23 | 234 | if (initcall_debug && system_state == SYSTEM_BOOTING) { |
22a9d645 AV |
235 | endtime = ktime_get(); |
236 | delta = ktime_sub(endtime, starttime); | |
237 | ||
238 | printk("async_continuing @ %i after %lli usec\n", | |
239 | task_pid_nr(current), ktime_to_ns(delta) >> 10); | |
240 | } | |
241 | } | |
242 | EXPORT_SYMBOL_GPL(async_synchronize_cookie_special); | |
243 | ||
244 | void async_synchronize_cookie(async_cookie_t cookie) | |
245 | { | |
246 | async_synchronize_cookie_special(cookie, &async_running); | |
247 | } | |
248 | EXPORT_SYMBOL_GPL(async_synchronize_cookie); | |
249 | ||
250 | ||
251 | static int async_thread(void *unused) | |
252 | { | |
253 | DECLARE_WAITQUEUE(wq, current); | |
254 | add_wait_queue(&async_new, &wq); | |
255 | ||
256 | while (!kthread_should_stop()) { | |
257 | int ret = HZ; | |
258 | set_current_state(TASK_INTERRUPTIBLE); | |
259 | /* | |
260 | * check the list head without lock.. false positives | |
261 | * are dealt with inside run_one_entry() while holding | |
262 | * the lock. | |
263 | */ | |
264 | rmb(); | |
265 | if (!list_empty(&async_pending)) | |
266 | run_one_entry(); | |
267 | else | |
268 | ret = schedule_timeout(HZ); | |
269 | ||
270 | if (ret == 0) { | |
271 | /* | |
272 | * we timed out, this means we as thread are redundant. | |
273 | * we sign off and die, but we to avoid any races there | |
274 | * is a last-straw check to see if work snuck in. | |
275 | */ | |
276 | atomic_dec(&thread_count); | |
277 | wmb(); /* manager must see our departure first */ | |
278 | if (list_empty(&async_pending)) | |
279 | break; | |
280 | /* | |
281 | * woops work came in between us timing out and us | |
282 | * signing off; we need to stay alive and keep working. | |
283 | */ | |
284 | atomic_inc(&thread_count); | |
285 | } | |
286 | } | |
287 | remove_wait_queue(&async_new, &wq); | |
288 | ||
289 | return 0; | |
290 | } | |
291 | ||
292 | static int async_manager_thread(void *unused) | |
293 | { | |
294 | DECLARE_WAITQUEUE(wq, current); | |
295 | add_wait_queue(&async_new, &wq); | |
296 | ||
297 | while (!kthread_should_stop()) { | |
298 | int tc, ec; | |
299 | ||
300 | set_current_state(TASK_INTERRUPTIBLE); | |
301 | ||
302 | tc = atomic_read(&thread_count); | |
303 | rmb(); | |
304 | ec = atomic_read(&entry_count); | |
305 | ||
306 | while (tc < ec && tc < MAX_THREADS) { | |
307 | kthread_run(async_thread, NULL, "async/%i", tc); | |
308 | atomic_inc(&thread_count); | |
309 | tc++; | |
310 | } | |
311 | ||
312 | schedule(); | |
313 | } | |
314 | remove_wait_queue(&async_new, &wq); | |
315 | ||
316 | return 0; | |
317 | } | |
318 | ||
319 | static int __init async_init(void) | |
320 | { | |
cdb80f63 AV |
321 | if (async_enabled) |
322 | kthread_run(async_manager_thread, NULL, "async/mgr"); | |
22a9d645 AV |
323 | return 0; |
324 | } | |
325 | ||
cdb80f63 AV |
326 | static int __init setup_async(char *str) |
327 | { | |
328 | async_enabled = 1; | |
329 | return 1; | |
330 | } | |
331 | ||
332 | __setup("fastboot", setup_async); | |
333 | ||
334 | ||
22a9d645 | 335 | core_initcall(async_init); |