2 * async.c: Asynchronous function calls for boot performance
4 * (C) Copyright 2009 Intel Corporation
5 * Author: Arjan van de Ven <arjan@linux.intel.com>
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
16 Goals and Theory of Operation
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.
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)
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).
32 The async core will assign each scheduled event such a sequence cookie and
33 pass this to the called functions.
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.
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.
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>
60 #include "workqueue_internal.h"
62 static async_cookie_t next_cookie = 1;
64 #define MAX_WORK 32768
66 static LIST_HEAD(async_pending);
67 static ASYNC_DOMAIN(async_running);
68 static LIST_HEAD(async_domains);
69 static DEFINE_SPINLOCK(async_lock);
70 static DEFINE_MUTEX(async_register_mutex);
73 struct list_head list;
74 struct work_struct work;
75 async_cookie_t cookie;
78 struct async_domain *running;
81 static DECLARE_WAIT_QUEUE_HEAD(async_done);
83 static atomic_t entry_count;
87 * MUST be called with the lock held!
89 static async_cookie_t __lowest_in_progress(struct async_domain *running)
91 struct async_entry *entry;
93 if (!list_empty(&running->domain)) {
94 entry = list_first_entry(&running->domain, typeof(*entry), list);
98 list_for_each_entry(entry, &async_pending, list)
99 if (entry->running == running)
100 return entry->cookie;
102 return next_cookie; /* "infinity" value */
105 static async_cookie_t lowest_in_progress(struct async_domain *running)
110 spin_lock_irqsave(&async_lock, flags);
111 ret = __lowest_in_progress(running);
112 spin_unlock_irqrestore(&async_lock, flags);
117 * pick the first pending entry and run it
119 static void async_run_entry_fn(struct work_struct *work)
121 struct async_entry *entry =
122 container_of(work, struct async_entry, work);
124 ktime_t uninitialized_var(calltime), delta, rettime;
125 struct async_domain *running = entry->running;
127 /* 1) move self to the running queue */
128 spin_lock_irqsave(&async_lock, flags);
129 list_move_tail(&entry->list, &running->domain);
130 spin_unlock_irqrestore(&async_lock, flags);
132 /* 2) run (and print duration) */
133 if (initcall_debug && system_state == SYSTEM_BOOTING) {
134 printk(KERN_DEBUG "calling %lli_%pF @ %i\n",
135 (long long)entry->cookie,
136 entry->func, task_pid_nr(current));
137 calltime = ktime_get();
139 entry->func(entry->data, entry->cookie);
140 if (initcall_debug && system_state == SYSTEM_BOOTING) {
141 rettime = ktime_get();
142 delta = ktime_sub(rettime, calltime);
143 printk(KERN_DEBUG "initcall %lli_%pF returned 0 after %lld usecs\n",
144 (long long)entry->cookie,
146 (long long)ktime_to_ns(delta) >> 10);
149 /* 3) remove self from the running queue */
150 spin_lock_irqsave(&async_lock, flags);
151 list_del(&entry->list);
152 if (running->registered && --running->count == 0)
153 list_del_init(&running->node);
155 /* 4) free the entry */
157 atomic_dec(&entry_count);
159 spin_unlock_irqrestore(&async_lock, flags);
161 /* 5) wake up any waiters */
162 wake_up(&async_done);
165 static async_cookie_t __async_schedule(async_func_ptr *ptr, void *data, struct async_domain *running)
167 struct async_entry *entry;
169 async_cookie_t newcookie;
171 /* allow irq-off callers */
172 entry = kzalloc(sizeof(struct async_entry), GFP_ATOMIC);
175 * If we're out of memory or if there's too much work
176 * pending already, we execute synchronously.
178 if (!entry || atomic_read(&entry_count) > MAX_WORK) {
180 spin_lock_irqsave(&async_lock, flags);
181 newcookie = next_cookie++;
182 spin_unlock_irqrestore(&async_lock, flags);
184 /* low on memory.. run synchronously */
185 ptr(data, newcookie);
188 INIT_WORK(&entry->work, async_run_entry_fn);
191 entry->running = running;
193 spin_lock_irqsave(&async_lock, flags);
194 newcookie = entry->cookie = next_cookie++;
195 list_add_tail(&entry->list, &async_pending);
196 if (running->registered && running->count++ == 0)
197 list_add_tail(&running->node, &async_domains);
198 atomic_inc(&entry_count);
199 spin_unlock_irqrestore(&async_lock, flags);
201 /* schedule for execution */
202 queue_work(system_unbound_wq, &entry->work);
208 * async_schedule - schedule a function for asynchronous execution
209 * @ptr: function to execute asynchronously
210 * @data: data pointer to pass to the function
212 * Returns an async_cookie_t that may be used for checkpointing later.
213 * Note: This function may be called from atomic or non-atomic contexts.
215 async_cookie_t async_schedule(async_func_ptr *ptr, void *data)
217 return __async_schedule(ptr, data, &async_running);
219 EXPORT_SYMBOL_GPL(async_schedule);
222 * async_schedule_domain - schedule a function for asynchronous execution within a certain domain
223 * @ptr: function to execute asynchronously
224 * @data: data pointer to pass to the function
225 * @running: running list for the domain
227 * Returns an async_cookie_t that may be used for checkpointing later.
228 * @running may be used in the async_synchronize_*_domain() functions
229 * to wait within a certain synchronization domain rather than globally.
230 * A synchronization domain is specified via the running queue @running to use.
231 * Note: This function may be called from atomic or non-atomic contexts.
233 async_cookie_t async_schedule_domain(async_func_ptr *ptr, void *data,
234 struct async_domain *running)
236 return __async_schedule(ptr, data, running);
238 EXPORT_SYMBOL_GPL(async_schedule_domain);
241 * async_synchronize_full - synchronize all asynchronous function calls
243 * This function waits until all asynchronous function calls have been done.
245 void async_synchronize_full(void)
247 mutex_lock(&async_register_mutex);
249 struct async_domain *domain = NULL;
251 spin_lock_irq(&async_lock);
252 if (!list_empty(&async_domains))
253 domain = list_first_entry(&async_domains, typeof(*domain), node);
254 spin_unlock_irq(&async_lock);
256 async_synchronize_cookie_domain(next_cookie, domain);
257 } while (!list_empty(&async_domains));
258 mutex_unlock(&async_register_mutex);
260 EXPORT_SYMBOL_GPL(async_synchronize_full);
263 * async_unregister_domain - ensure no more anonymous waiters on this domain
264 * @domain: idle domain to flush out of any async_synchronize_full instances
266 * async_synchronize_{cookie|full}_domain() are not flushed since callers
267 * of these routines should know the lifetime of @domain
269 * Prefer ASYNC_DOMAIN_EXCLUSIVE() declarations over flushing
271 void async_unregister_domain(struct async_domain *domain)
273 mutex_lock(&async_register_mutex);
274 spin_lock_irq(&async_lock);
275 WARN_ON(!domain->registered || !list_empty(&domain->node) ||
276 !list_empty(&domain->domain));
277 domain->registered = 0;
278 spin_unlock_irq(&async_lock);
279 mutex_unlock(&async_register_mutex);
281 EXPORT_SYMBOL_GPL(async_unregister_domain);
284 * async_synchronize_full_domain - synchronize all asynchronous function within a certain domain
285 * @domain: running list to synchronize on
287 * This function waits until all asynchronous function calls for the
288 * synchronization domain specified by the running list @domain have been done.
290 void async_synchronize_full_domain(struct async_domain *domain)
292 async_synchronize_cookie_domain(next_cookie, domain);
294 EXPORT_SYMBOL_GPL(async_synchronize_full_domain);
297 * async_synchronize_cookie_domain - synchronize asynchronous function calls within a certain domain with cookie checkpointing
298 * @cookie: async_cookie_t to use as checkpoint
299 * @running: running list to synchronize on
301 * This function waits until all asynchronous function calls for the
302 * synchronization domain specified by running list @running submitted
303 * prior to @cookie have been done.
305 void async_synchronize_cookie_domain(async_cookie_t cookie, struct async_domain *running)
307 ktime_t uninitialized_var(starttime), delta, endtime;
312 if (initcall_debug && system_state == SYSTEM_BOOTING) {
313 printk(KERN_DEBUG "async_waiting @ %i\n", task_pid_nr(current));
314 starttime = ktime_get();
317 wait_event(async_done, lowest_in_progress(running) >= cookie);
319 if (initcall_debug && system_state == SYSTEM_BOOTING) {
320 endtime = ktime_get();
321 delta = ktime_sub(endtime, starttime);
323 printk(KERN_DEBUG "async_continuing @ %i after %lli usec\n",
324 task_pid_nr(current),
325 (long long)ktime_to_ns(delta) >> 10);
328 EXPORT_SYMBOL_GPL(async_synchronize_cookie_domain);
331 * async_synchronize_cookie - synchronize asynchronous function calls with cookie checkpointing
332 * @cookie: async_cookie_t to use as checkpoint
334 * This function waits until all asynchronous function calls prior to @cookie
337 void async_synchronize_cookie(async_cookie_t cookie)
339 async_synchronize_cookie_domain(cookie, &async_running);
341 EXPORT_SYMBOL_GPL(async_synchronize_cookie);
344 * current_is_async - is %current an async worker task?
346 * Returns %true if %current is an async worker task.
348 bool current_is_async(void)
350 struct worker *worker = current_wq_worker();
352 return worker && worker->current_func == async_run_entry_fn;