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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/module.h> | |
53 | #include <linux/wait.h> | |
54 | #include <linux/sched.h> | |
55 | #include <linux/slab.h> | |
56 | #include <linux/workqueue.h> | |
57 | #include <asm/atomic.h> | |
58 | ||
59 | static async_cookie_t next_cookie = 1; | |
60 | ||
61 | #define MAX_WORK 32768 | |
62 | ||
63 | static LIST_HEAD(async_pending); | |
64 | static LIST_HEAD(async_running); | |
65 | static DEFINE_SPINLOCK(async_lock); | |
66 | ||
67 | struct async_entry { | |
68 | struct list_head list; | |
69 | struct work_struct work; | |
70 | async_cookie_t cookie; | |
71 | async_func_ptr *func; | |
72 | void *data; | |
73 | struct list_head *running; | |
74 | }; | |
75 | ||
76 | static DECLARE_WAIT_QUEUE_HEAD(async_done); | |
77 | ||
78 | static atomic_t entry_count; | |
79 | ||
80 | extern int initcall_debug; | |
81 | ||
82 | ||
83 | /* | |
84 | * MUST be called with the lock held! | |
85 | */ | |
86 | static async_cookie_t __lowest_in_progress(struct list_head *running) | |
87 | { | |
88 | struct async_entry *entry; | |
89 | ||
90 | if (!list_empty(running)) { | |
91 | entry = list_first_entry(running, | |
92 | struct async_entry, list); | |
93 | return entry->cookie; | |
94 | } | |
95 | ||
96 | list_for_each_entry(entry, &async_pending, list) | |
97 | if (entry->running == running) | |
98 | return entry->cookie; | |
99 | ||
100 | return next_cookie; /* "infinity" value */ | |
101 | } | |
102 | ||
103 | static async_cookie_t lowest_in_progress(struct list_head *running) | |
104 | { | |
105 | unsigned long flags; | |
106 | async_cookie_t ret; | |
107 | ||
108 | spin_lock_irqsave(&async_lock, flags); | |
109 | ret = __lowest_in_progress(running); | |
110 | spin_unlock_irqrestore(&async_lock, flags); | |
111 | return ret; | |
112 | } | |
113 | ||
114 | /* | |
115 | * pick the first pending entry and run it | |
116 | */ | |
117 | static void async_run_entry_fn(struct work_struct *work) | |
118 | { | |
119 | struct async_entry *entry = | |
120 | container_of(work, struct async_entry, work); | |
121 | unsigned long flags; | |
122 | ktime_t calltime, delta, rettime; | |
123 | ||
124 | /* 1) move self to the running queue */ | |
125 | spin_lock_irqsave(&async_lock, flags); | |
126 | list_move_tail(&entry->list, entry->running); | |
127 | spin_unlock_irqrestore(&async_lock, flags); | |
128 | ||
129 | /* 2) run (and print duration) */ | |
130 | if (initcall_debug && system_state == SYSTEM_BOOTING) { | |
131 | printk("calling %lli_%pF @ %i\n", (long long)entry->cookie, | |
132 | entry->func, task_pid_nr(current)); | |
133 | calltime = ktime_get(); | |
134 | } | |
135 | entry->func(entry->data, entry->cookie); | |
136 | if (initcall_debug && system_state == SYSTEM_BOOTING) { | |
137 | rettime = ktime_get(); | |
138 | delta = ktime_sub(rettime, calltime); | |
139 | printk("initcall %lli_%pF returned 0 after %lld usecs\n", | |
140 | (long long)entry->cookie, | |
141 | entry->func, | |
142 | (long long)ktime_to_ns(delta) >> 10); | |
143 | } | |
144 | ||
145 | /* 3) remove self from the running queue */ | |
146 | spin_lock_irqsave(&async_lock, flags); | |
147 | list_del(&entry->list); | |
148 | ||
149 | /* 4) free the entry */ | |
150 | kfree(entry); | |
151 | atomic_dec(&entry_count); | |
152 | ||
153 | spin_unlock_irqrestore(&async_lock, flags); | |
154 | ||
155 | /* 5) wake up any waiters */ | |
156 | wake_up(&async_done); | |
157 | } | |
158 | ||
159 | static async_cookie_t __async_schedule(async_func_ptr *ptr, void *data, struct list_head *running) | |
160 | { | |
161 | struct async_entry *entry; | |
162 | unsigned long flags; | |
163 | async_cookie_t newcookie; | |
164 | ||
165 | /* allow irq-off callers */ | |
166 | entry = kzalloc(sizeof(struct async_entry), GFP_ATOMIC); | |
167 | ||
168 | /* | |
169 | * If we're out of memory or if there's too much work | |
170 | * pending already, we execute synchronously. | |
171 | */ | |
172 | if (!entry || atomic_read(&entry_count) > MAX_WORK) { | |
173 | kfree(entry); | |
174 | spin_lock_irqsave(&async_lock, flags); | |
175 | newcookie = next_cookie++; | |
176 | spin_unlock_irqrestore(&async_lock, flags); | |
177 | ||
178 | /* low on memory.. run synchronously */ | |
179 | ptr(data, newcookie); | |
180 | return newcookie; | |
181 | } | |
182 | INIT_WORK(&entry->work, async_run_entry_fn); | |
183 | entry->func = ptr; | |
184 | entry->data = data; | |
185 | entry->running = running; | |
186 | ||
187 | spin_lock_irqsave(&async_lock, flags); | |
188 | newcookie = entry->cookie = next_cookie++; | |
189 | list_add_tail(&entry->list, &async_pending); | |
190 | atomic_inc(&entry_count); | |
191 | spin_unlock_irqrestore(&async_lock, flags); | |
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 | * @ptr: 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_ptr *ptr, void *data) | |
208 | { | |
209 | return __async_schedule(ptr, data, &async_running); | |
210 | } | |
211 | EXPORT_SYMBOL_GPL(async_schedule); | |
212 | ||
213 | /** | |
214 | * async_schedule_domain - schedule a function for asynchronous execution within a certain domain | |
215 | * @ptr: function to execute asynchronously | |
216 | * @data: data pointer to pass to the function | |
217 | * @running: running list for the domain | |
218 | * | |
219 | * Returns an async_cookie_t that may be used for checkpointing later. | |
220 | * @running may be used in the async_synchronize_*_domain() functions | |
221 | * to wait within a certain synchronization domain rather than globally. | |
222 | * A synchronization domain is specified via the running queue @running to use. | |
223 | * Note: This function may be called from atomic or non-atomic contexts. | |
224 | */ | |
225 | async_cookie_t async_schedule_domain(async_func_ptr *ptr, void *data, | |
226 | struct list_head *running) | |
227 | { | |
228 | return __async_schedule(ptr, data, running); | |
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 | do { | |
240 | async_synchronize_cookie(next_cookie); | |
241 | } while (!list_empty(&async_running) || !list_empty(&async_pending)); | |
242 | } | |
243 | EXPORT_SYMBOL_GPL(async_synchronize_full); | |
244 | ||
245 | /** | |
246 | * async_synchronize_full_domain - synchronize all asynchronous function within a certain domain | |
247 | * @list: running list to synchronize on | |
248 | * | |
249 | * This function waits until all asynchronous function calls for the | |
250 | * synchronization domain specified by the running list @list have been done. | |
251 | */ | |
252 | void async_synchronize_full_domain(struct list_head *list) | |
253 | { | |
254 | async_synchronize_cookie_domain(next_cookie, list); | |
255 | } | |
256 | EXPORT_SYMBOL_GPL(async_synchronize_full_domain); | |
257 | ||
258 | /** | |
259 | * async_synchronize_cookie_domain - synchronize asynchronous function calls within a certain domain with cookie checkpointing | |
260 | * @cookie: async_cookie_t to use as checkpoint | |
261 | * @running: running list to synchronize on | |
262 | * | |
263 | * This function waits until all asynchronous function calls for the | |
264 | * synchronization domain specified by the running list @list submitted | |
265 | * prior to @cookie have been done. | |
266 | */ | |
267 | void async_synchronize_cookie_domain(async_cookie_t cookie, | |
268 | struct list_head *running) | |
269 | { | |
270 | ktime_t starttime, delta, endtime; | |
271 | ||
272 | if (initcall_debug && system_state == SYSTEM_BOOTING) { | |
273 | printk("async_waiting @ %i\n", task_pid_nr(current)); | |
274 | starttime = ktime_get(); | |
275 | } | |
276 | ||
277 | wait_event(async_done, lowest_in_progress(running) >= cookie); | |
278 | ||
279 | if (initcall_debug && system_state == SYSTEM_BOOTING) { | |
280 | endtime = ktime_get(); | |
281 | delta = ktime_sub(endtime, starttime); | |
282 | ||
283 | printk("async_continuing @ %i after %lli usec\n", | |
284 | task_pid_nr(current), | |
285 | (long long)ktime_to_ns(delta) >> 10); | |
286 | } | |
287 | } | |
288 | EXPORT_SYMBOL_GPL(async_synchronize_cookie_domain); | |
289 | ||
290 | /** | |
291 | * async_synchronize_cookie - synchronize asynchronous function calls with cookie checkpointing | |
292 | * @cookie: async_cookie_t to use as checkpoint | |
293 | * | |
294 | * This function waits until all asynchronous function calls prior to @cookie | |
295 | * have been done. | |
296 | */ | |
297 | void async_synchronize_cookie(async_cookie_t cookie) | |
298 | { | |
299 | async_synchronize_cookie_domain(cookie, &async_running); | |
300 | } | |
301 | EXPORT_SYMBOL_GPL(async_synchronize_cookie); |