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Linux/kernel/async.c

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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 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_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 
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  */
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  */
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  */
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_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  */
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 EXPORT_SYMBOL_GPL(current_is_async);
334 

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