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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_ptr *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 async_entry *first = NULL; |
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 | if (!list_empty(&domain->pending)) |
95 | first = list_first_entry(&domain->pending, |
96 | struct async_entry, domain_list); |
97 | } else { |
98 | if (!list_empty(&async_global_pending)) |
99 | first = list_first_entry(&async_global_pending, |
100 | struct async_entry, global_list); |
101 | } |
102 | |
103 | if (first) |
104 | ret = first->cookie; |
105 | |
106 | spin_unlock_irqrestore(&async_lock, flags); |
107 | return ret; |
108 | } |
109 | |
110 | /* |
111 | * pick the first pending entry and run it |
112 | */ |
113 | static void async_run_entry_fn(struct work_struct *work) |
114 | { |
115 | struct async_entry *entry = |
116 | container_of(work, struct async_entry, work); |
117 | unsigned long flags; |
118 | ktime_t uninitialized_var(calltime), delta, rettime; |
119 | |
120 | /* 1) run (and print duration) */ |
121 | if (initcall_debug && system_state == SYSTEM_BOOTING) { |
122 | printk(KERN_DEBUG "calling %lli_%pF @ %i\n", |
123 | (long long)entry->cookie, |
124 | entry->func, task_pid_nr(current)); |
125 | calltime = ktime_get(); |
126 | } |
127 | entry->func(entry->data, entry->cookie); |
128 | if (initcall_debug && system_state == SYSTEM_BOOTING) { |
129 | rettime = ktime_get(); |
130 | delta = ktime_sub(rettime, calltime); |
131 | printk(KERN_DEBUG "initcall %lli_%pF returned 0 after %lld usecs\n", |
132 | (long long)entry->cookie, |
133 | entry->func, |
134 | (long long)ktime_to_ns(delta) >> 10); |
135 | } |
136 | |
137 | /* 2) remove self from the pending queues */ |
138 | spin_lock_irqsave(&async_lock, flags); |
139 | list_del_init(&entry->domain_list); |
140 | list_del_init(&entry->global_list); |
141 | |
142 | /* 3) free the entry */ |
143 | kfree(entry); |
144 | atomic_dec(&entry_count); |
145 | |
146 | spin_unlock_irqrestore(&async_lock, flags); |
147 | |
148 | /* 4) wake up any waiters */ |
149 | wake_up(&async_done); |
150 | } |
151 | |
152 | static async_cookie_t __async_schedule(async_func_ptr *ptr, void *data, struct async_domain *domain) |
153 | { |
154 | struct async_entry *entry; |
155 | unsigned long flags; |
156 | async_cookie_t newcookie; |
157 | |
158 | /* allow irq-off callers */ |
159 | entry = kzalloc(sizeof(struct async_entry), GFP_ATOMIC); |
160 | |
161 | /* |
162 | * If we're out of memory or if there's too much work |
163 | * pending already, we execute synchronously. |
164 | */ |
165 | if (!entry || atomic_read(&entry_count) > MAX_WORK) { |
166 | kfree(entry); |
167 | spin_lock_irqsave(&async_lock, flags); |
168 | newcookie = next_cookie++; |
169 | spin_unlock_irqrestore(&async_lock, flags); |
170 | |
171 | /* low on memory.. run synchronously */ |
172 | ptr(data, newcookie); |
173 | return newcookie; |
174 | } |
175 | INIT_LIST_HEAD(&entry->domain_list); |
176 | INIT_LIST_HEAD(&entry->global_list); |
177 | INIT_WORK(&entry->work, async_run_entry_fn); |
178 | entry->func = ptr; |
179 | entry->data = data; |
180 | entry->domain = domain; |
181 | |
182 | spin_lock_irqsave(&async_lock, flags); |
183 | |
184 | /* allocate cookie and queue */ |
185 | newcookie = entry->cookie = next_cookie++; |
186 | |
187 | list_add_tail(&entry->domain_list, &domain->pending); |
188 | if (domain->registered) |
189 | list_add_tail(&entry->global_list, &async_global_pending); |
190 | |
191 | atomic_inc(&entry_count); |
192 | spin_unlock_irqrestore(&async_lock, flags); |
193 | |
194 | /* mark that this task has queued an async job, used by module init */ |
195 | current->flags |= PF_USED_ASYNC; |
196 | |
197 | /* schedule for execution */ |
198 | queue_work(system_unbound_wq, &entry->work); |
199 | |
200 | return newcookie; |
201 | } |
202 | |
203 | /** |
204 | * async_schedule - schedule a function for asynchronous execution |
205 | * @ptr: function to execute asynchronously |
206 | * @data: data pointer to pass to the function |
207 | * |
208 | * Returns an async_cookie_t that may be used for checkpointing later. |
209 | * Note: This function may be called from atomic or non-atomic contexts. |
210 | */ |
211 | async_cookie_t async_schedule(async_func_ptr *ptr, void *data) |
212 | { |
213 | return __async_schedule(ptr, data, &async_dfl_domain); |
214 | } |
215 | EXPORT_SYMBOL_GPL(async_schedule); |
216 | |
217 | /** |
218 | * async_schedule_domain - schedule a function for asynchronous execution within a certain domain |
219 | * @ptr: function to execute asynchronously |
220 | * @data: data pointer to pass to the function |
221 | * @domain: the domain |
222 | * |
223 | * Returns an async_cookie_t that may be used for checkpointing later. |
224 | * @domain may be used in the async_synchronize_*_domain() functions to |
225 | * wait within a certain synchronization domain rather than globally. A |
226 | * synchronization domain is specified via @domain. Note: This function |
227 | * may be called from atomic or non-atomic contexts. |
228 | */ |
229 | async_cookie_t async_schedule_domain(async_func_ptr *ptr, void *data, |
230 | struct async_domain *domain) |
231 | { |
232 | return __async_schedule(ptr, data, domain); |
233 | } |
234 | EXPORT_SYMBOL_GPL(async_schedule_domain); |
235 | |
236 | /** |
237 | * async_synchronize_full - synchronize all asynchronous function calls |
238 | * |
239 | * This function waits until all asynchronous function calls have been done. |
240 | */ |
241 | void async_synchronize_full(void) |
242 | { |
243 | async_synchronize_full_domain(NULL); |
244 | } |
245 | EXPORT_SYMBOL_GPL(async_synchronize_full); |
246 | |
247 | /** |
248 | * async_unregister_domain - ensure no more anonymous waiters on this domain |
249 | * @domain: idle domain to flush out of any async_synchronize_full instances |
250 | * |
251 | * async_synchronize_{cookie|full}_domain() are not flushed since callers |
252 | * of these routines should know the lifetime of @domain |
253 | * |
254 | * Prefer ASYNC_DOMAIN_EXCLUSIVE() declarations over flushing |
255 | */ |
256 | void async_unregister_domain(struct async_domain *domain) |
257 | { |
258 | spin_lock_irq(&async_lock); |
259 | WARN_ON(!domain->registered || !list_empty(&domain->pending)); |
260 | domain->registered = 0; |
261 | spin_unlock_irq(&async_lock); |
262 | } |
263 | EXPORT_SYMBOL_GPL(async_unregister_domain); |
264 | |
265 | /** |
266 | * async_synchronize_full_domain - synchronize all asynchronous function within a certain domain |
267 | * @domain: the domain to synchronize |
268 | * |
269 | * This function waits until all asynchronous function calls for the |
270 | * synchronization domain specified by @domain have been done. |
271 | */ |
272 | void async_synchronize_full_domain(struct async_domain *domain) |
273 | { |
274 | async_synchronize_cookie_domain(ASYNC_COOKIE_MAX, domain); |
275 | } |
276 | EXPORT_SYMBOL_GPL(async_synchronize_full_domain); |
277 | |
278 | /** |
279 | * async_synchronize_cookie_domain - synchronize asynchronous function calls within a certain domain with cookie checkpointing |
280 | * @cookie: async_cookie_t to use as checkpoint |
281 | * @domain: the domain to synchronize (%NULL for all registered domains) |
282 | * |
283 | * This function waits until all asynchronous function calls for the |
284 | * synchronization domain specified by @domain submitted prior to @cookie |
285 | * have been done. |
286 | */ |
287 | void async_synchronize_cookie_domain(async_cookie_t cookie, struct async_domain *domain) |
288 | { |
289 | ktime_t uninitialized_var(starttime), delta, endtime; |
290 | |
291 | if (initcall_debug && system_state == SYSTEM_BOOTING) { |
292 | printk(KERN_DEBUG "async_waiting @ %i\n", task_pid_nr(current)); |
293 | starttime = ktime_get(); |
294 | } |
295 | |
296 | wait_event(async_done, lowest_in_progress(domain) >= cookie); |
297 | |
298 | if (initcall_debug && system_state == SYSTEM_BOOTING) { |
299 | endtime = ktime_get(); |
300 | delta = ktime_sub(endtime, starttime); |
301 | |
302 | printk(KERN_DEBUG "async_continuing @ %i after %lli usec\n", |
303 | task_pid_nr(current), |
304 | (long long)ktime_to_ns(delta) >> 10); |
305 | } |
306 | } |
307 | EXPORT_SYMBOL_GPL(async_synchronize_cookie_domain); |
308 | |
309 | /** |
310 | * async_synchronize_cookie - synchronize asynchronous function calls with cookie checkpointing |
311 | * @cookie: async_cookie_t to use as checkpoint |
312 | * |
313 | * This function waits until all asynchronous function calls prior to @cookie |
314 | * have been done. |
315 | */ |
316 | void async_synchronize_cookie(async_cookie_t cookie) |
317 | { |
318 | async_synchronize_cookie_domain(cookie, &async_dfl_domain); |
319 | } |
320 | EXPORT_SYMBOL_GPL(async_synchronize_cookie); |
321 | |
322 | /** |
323 | * current_is_async - is %current an async worker task? |
324 | * |
325 | * Returns %true if %current is an async worker task. |
326 | */ |
327 | bool current_is_async(void) |
328 | { |
329 | struct worker *worker = current_wq_worker(); |
330 | |
331 | return worker && worker->current_func == async_run_entry_fn; |
332 | } |
333 |
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