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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/atomic.h> | |
53 | #include <linux/ktime.h> | |
54 | #include <linux/export.h> | |
55 | #include <linux/wait.h> | |
56 | #include <linux/sched.h> | |
57 | #include <linux/slab.h> | |
58 | #include <linux/workqueue.h> | |
59 | ||
60 | #include "workqueue_internal.h" | |
61 | ||
62 | static async_cookie_t next_cookie = 1; | |
63 | ||
64 | #define MAX_WORK 32768 | |
65 | #define ASYNC_COOKIE_MAX ULLONG_MAX /* infinity cookie */ | |
66 | ||
67 | static LIST_HEAD(async_global_pending); /* pending from all registered doms */ | |
68 | static ASYNC_DOMAIN(async_dfl_domain); | |
69 | static DEFINE_SPINLOCK(async_lock); | |
70 | ||
71 | struct async_entry { | |
72 | struct list_head domain_list; | |
73 | struct list_head global_list; | |
74 | struct work_struct work; | |
75 | async_cookie_t cookie; | |
76 | async_func_t func; | |
77 | void *data; | |
78 | struct async_domain *domain; | |
79 | }; | |
80 | ||
81 | static DECLARE_WAIT_QUEUE_HEAD(async_done); | |
82 | ||
83 | static atomic_t entry_count; | |
84 | ||
85 | static async_cookie_t lowest_in_progress(struct async_domain *domain) | |
86 | { | |
87 | struct list_head *pending; | |
88 | async_cookie_t ret = ASYNC_COOKIE_MAX; | |
89 | unsigned long flags; | |
90 | ||
91 | spin_lock_irqsave(&async_lock, flags); | |
92 | ||
93 | if (domain) | |
94 | pending = &domain->pending; | |
95 | else | |
96 | pending = &async_global_pending; | |
97 | ||
98 | if (!list_empty(pending)) | |
99 | ret = list_first_entry(pending, struct async_entry, | |
100 | domain_list)->cookie; | |
101 | ||
102 | spin_unlock_irqrestore(&async_lock, flags); | |
103 | return ret; | |
104 | } | |
105 | ||
106 | /* | |
107 | * pick the first pending entry and run it | |
108 | */ | |
109 | static void async_run_entry_fn(struct work_struct *work) | |
110 | { | |
111 | struct async_entry *entry = | |
112 | container_of(work, struct async_entry, work); | |
113 | unsigned long flags; | |
114 | ktime_t uninitialized_var(calltime), delta, rettime; | |
115 | ||
116 | /* 1) run (and print duration) */ | |
117 | if (initcall_debug && system_state == SYSTEM_BOOTING) { | |
118 | pr_debug("calling %lli_%pF @ %i\n", | |
119 | (long long)entry->cookie, | |
120 | entry->func, task_pid_nr(current)); | |
121 | calltime = ktime_get(); | |
122 | } | |
123 | entry->func(entry->data, entry->cookie); | |
124 | if (initcall_debug && system_state == SYSTEM_BOOTING) { | |
125 | rettime = ktime_get(); | |
126 | delta = ktime_sub(rettime, calltime); | |
127 | pr_debug("initcall %lli_%pF returned 0 after %lld usecs\n", | |
128 | (long long)entry->cookie, | |
129 | entry->func, | |
130 | (long long)ktime_to_ns(delta) >> 10); | |
131 | } | |
132 | ||
133 | /* 2) remove self from the pending queues */ | |
134 | spin_lock_irqsave(&async_lock, flags); | |
135 | list_del_init(&entry->domain_list); | |
136 | list_del_init(&entry->global_list); | |
137 | ||
138 | /* 3) free the entry */ | |
139 | kfree(entry); | |
140 | atomic_dec(&entry_count); | |
141 | ||
142 | spin_unlock_irqrestore(&async_lock, flags); | |
143 | ||
144 | /* 4) wake up any waiters */ | |
145 | wake_up(&async_done); | |
146 | } | |
147 | ||
148 | static async_cookie_t __async_schedule(async_func_t func, void *data, struct async_domain *domain) | |
149 | { | |
150 | struct async_entry *entry; | |
151 | unsigned long flags; | |
152 | async_cookie_t newcookie; | |
153 | ||
154 | /* allow irq-off callers */ | |
155 | entry = kzalloc(sizeof(struct async_entry), GFP_ATOMIC); | |
156 | ||
157 | /* | |
158 | * If we're out of memory or if there's too much work | |
159 | * pending already, we execute synchronously. | |
160 | */ | |
161 | if (!entry || atomic_read(&entry_count) > MAX_WORK) { | |
162 | kfree(entry); | |
163 | spin_lock_irqsave(&async_lock, flags); | |
164 | newcookie = next_cookie++; | |
165 | spin_unlock_irqrestore(&async_lock, flags); | |
166 | ||
167 | /* low on memory.. run synchronously */ | |
168 | func(data, newcookie); | |
169 | return newcookie; | |
170 | } | |
171 | INIT_LIST_HEAD(&entry->domain_list); | |
172 | INIT_LIST_HEAD(&entry->global_list); | |
173 | INIT_WORK(&entry->work, async_run_entry_fn); | |
174 | entry->func = func; | |
175 | entry->data = data; | |
176 | entry->domain = domain; | |
177 | ||
178 | spin_lock_irqsave(&async_lock, flags); | |
179 | ||
180 | /* allocate cookie and queue */ | |
181 | newcookie = entry->cookie = next_cookie++; | |
182 | ||
183 | list_add_tail(&entry->domain_list, &domain->pending); | |
184 | if (domain->registered) | |
185 | list_add_tail(&entry->global_list, &async_global_pending); | |
186 | ||
187 | atomic_inc(&entry_count); | |
188 | spin_unlock_irqrestore(&async_lock, flags); | |
189 | ||
190 | /* mark that this task has queued an async job, used by module init */ | |
191 | current->flags |= PF_USED_ASYNC; | |
192 | ||
193 | /* schedule for execution */ | |
194 | queue_work(system_unbound_wq, &entry->work); | |
195 | ||
196 | return newcookie; | |
197 | } | |
198 | ||
199 | /** | |
200 | * async_schedule - schedule a function for asynchronous execution | |
201 | * @func: function to execute asynchronously | |
202 | * @data: data pointer to pass to the function | |
203 | * | |
204 | * Returns an async_cookie_t that may be used for checkpointing later. | |
205 | * Note: This function may be called from atomic or non-atomic contexts. | |
206 | */ | |
207 | async_cookie_t async_schedule(async_func_t func, void *data) | |
208 | { | |
209 | return __async_schedule(func, data, &async_dfl_domain); | |
210 | } | |
211 | EXPORT_SYMBOL_GPL(async_schedule); | |
212 | ||
213 | /** | |
214 | * async_schedule_domain - schedule a function for asynchronous execution within a certain domain | |
215 | * @func: function to execute asynchronously | |
216 | * @data: data pointer to pass to the function | |
217 | * @domain: the domain | |
218 | * | |
219 | * Returns an async_cookie_t that may be used for checkpointing later. | |
220 | * @domain may be used in the async_synchronize_*_domain() functions to | |
221 | * wait within a certain synchronization domain rather than globally. A | |
222 | * synchronization domain is specified via @domain. Note: This function | |
223 | * may be called from atomic or non-atomic contexts. | |
224 | */ | |
225 | async_cookie_t async_schedule_domain(async_func_t func, void *data, | |
226 | struct async_domain *domain) | |
227 | { | |
228 | return __async_schedule(func, data, domain); | |
229 | } | |
230 | EXPORT_SYMBOL_GPL(async_schedule_domain); | |
231 | ||
232 | /** | |
233 | * async_synchronize_full - synchronize all asynchronous function calls | |
234 | * | |
235 | * This function waits until all asynchronous function calls have been done. | |
236 | */ | |
237 | void async_synchronize_full(void) | |
238 | { | |
239 | async_synchronize_full_domain(NULL); | |
240 | } | |
241 | EXPORT_SYMBOL_GPL(async_synchronize_full); | |
242 | ||
243 | /** | |
244 | * async_unregister_domain - ensure no more anonymous waiters on this domain | |
245 | * @domain: idle domain to flush out of any async_synchronize_full instances | |
246 | * | |
247 | * async_synchronize_{cookie|full}_domain() are not flushed since callers | |
248 | * of these routines should know the lifetime of @domain | |
249 | * | |
250 | * Prefer ASYNC_DOMAIN_EXCLUSIVE() declarations over flushing | |
251 | */ | |
252 | void async_unregister_domain(struct async_domain *domain) | |
253 | { | |
254 | spin_lock_irq(&async_lock); | |
255 | WARN_ON(!domain->registered || !list_empty(&domain->pending)); | |
256 | domain->registered = 0; | |
257 | spin_unlock_irq(&async_lock); | |
258 | } | |
259 | EXPORT_SYMBOL_GPL(async_unregister_domain); | |
260 | ||
261 | /** | |
262 | * async_synchronize_full_domain - synchronize all asynchronous function within a certain domain | |
263 | * @domain: the domain to synchronize | |
264 | * | |
265 | * This function waits until all asynchronous function calls for the | |
266 | * synchronization domain specified by @domain have been done. | |
267 | */ | |
268 | void async_synchronize_full_domain(struct async_domain *domain) | |
269 | { | |
270 | async_synchronize_cookie_domain(ASYNC_COOKIE_MAX, domain); | |
271 | } | |
272 | EXPORT_SYMBOL_GPL(async_synchronize_full_domain); | |
273 | ||
274 | /** | |
275 | * async_synchronize_cookie_domain - synchronize asynchronous function calls within a certain domain with cookie checkpointing | |
276 | * @cookie: async_cookie_t to use as checkpoint | |
277 | * @domain: the domain to synchronize (%NULL for all registered domains) | |
278 | * | |
279 | * This function waits until all asynchronous function calls for the | |
280 | * synchronization domain specified by @domain submitted prior to @cookie | |
281 | * have been done. | |
282 | */ | |
283 | void async_synchronize_cookie_domain(async_cookie_t cookie, struct async_domain *domain) | |
284 | { | |
285 | ktime_t uninitialized_var(starttime), delta, endtime; | |
286 | ||
287 | if (initcall_debug && system_state == SYSTEM_BOOTING) { | |
288 | pr_debug("async_waiting @ %i\n", task_pid_nr(current)); | |
289 | starttime = ktime_get(); | |
290 | } | |
291 | ||
292 | wait_event(async_done, lowest_in_progress(domain) >= cookie); | |
293 | ||
294 | if (initcall_debug && system_state == SYSTEM_BOOTING) { | |
295 | endtime = ktime_get(); | |
296 | delta = ktime_sub(endtime, starttime); | |
297 | ||
298 | pr_debug("async_continuing @ %i after %lli usec\n", | |
299 | task_pid_nr(current), | |
300 | (long long)ktime_to_ns(delta) >> 10); | |
301 | } | |
302 | } | |
303 | EXPORT_SYMBOL_GPL(async_synchronize_cookie_domain); | |
304 | ||
305 | /** | |
306 | * async_synchronize_cookie - synchronize asynchronous function calls with cookie checkpointing | |
307 | * @cookie: async_cookie_t to use as checkpoint | |
308 | * | |
309 | * This function waits until all asynchronous function calls prior to @cookie | |
310 | * have been done. | |
311 | */ | |
312 | void async_synchronize_cookie(async_cookie_t cookie) | |
313 | { | |
314 | async_synchronize_cookie_domain(cookie, &async_dfl_domain); | |
315 | } | |
316 | EXPORT_SYMBOL_GPL(async_synchronize_cookie); | |
317 | ||
318 | /** | |
319 | * current_is_async - is %current an async worker task? | |
320 | * | |
321 | * Returns %true if %current is an async worker task. | |
322 | */ | |
323 | bool current_is_async(void) | |
324 | { | |
325 | struct worker *worker = current_wq_worker(); | |
326 | ||
327 | return worker && worker->current_func == async_run_entry_fn; | |
328 | } | |
329 | EXPORT_SYMBOL_GPL(current_is_async); |