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
lowest_in_progress(struct async_domain * domain)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 */
async_run_entry_fn(struct work_struct * work)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_RUNNING) {
122 pr_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_RUNNING) {
129 rettime = ktime_get();
130 delta = ktime_sub(rettime, calltime);
131 pr_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
__async_schedule(async_func_t func,void * data,struct async_domain * domain)152 static async_cookie_t __async_schedule(async_func_t func, 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 func(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 = func;
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 * @func: 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 */
async_schedule(async_func_t func,void * data)211 async_cookie_t async_schedule(async_func_t func, void *data)
212 {
213 return __async_schedule(func, 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 * @func: 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 */
async_schedule_domain(async_func_t func,void * data,struct async_domain * domain)229 async_cookie_t async_schedule_domain(async_func_t func, void *data,
230 struct async_domain *domain)
231 {
232 return __async_schedule(func, 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 */
async_synchronize_full(void)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 */
async_unregister_domain(struct async_domain * domain)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 */
async_synchronize_full_domain(struct async_domain * domain)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 */
async_synchronize_cookie_domain(async_cookie_t cookie,struct async_domain * domain)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_RUNNING) {
292 pr_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_RUNNING) {
299 endtime = ktime_get();
300 delta = ktime_sub(endtime, starttime);
301
302 pr_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 */
async_synchronize_cookie(async_cookie_t cookie)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 */
current_is_async(void)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 EXPORT_SYMBOL_GPL(current_is_async);
334
