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
65 #define ASYNC_COOKIE_MAX ULLONG_MAX /* infinity cookie */
67 static ASYNC_DOMAIN(async_dfl_domain);
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 *domain;
81 static DECLARE_WAIT_QUEUE_HEAD(async_done);
83 static atomic_t entry_count;
85 static async_cookie_t lowest_in_progress(struct async_domain *domain)
87 async_cookie_t ret = ASYNC_COOKIE_MAX;
90 spin_lock_irqsave(&async_lock, flags);
91 if (!list_empty(&domain->pending)) {
92 struct async_entry *first = list_first_entry(&domain->pending,
93 struct async_entry, list);
96 spin_unlock_irqrestore(&async_lock, flags);
101 * pick the first pending entry and run it
103 static void async_run_entry_fn(struct work_struct *work)
105 struct async_entry *entry =
106 container_of(work, struct async_entry, work);
108 ktime_t uninitialized_var(calltime), delta, rettime;
109 struct async_domain *domain = entry->domain;
111 /* 1) run (and print duration) */
112 if (initcall_debug && system_state == SYSTEM_BOOTING) {
113 printk(KERN_DEBUG "calling %lli_%pF @ %i\n",
114 (long long)entry->cookie,
115 entry->func, task_pid_nr(current));
116 calltime = ktime_get();
118 entry->func(entry->data, entry->cookie);
119 if (initcall_debug && system_state == SYSTEM_BOOTING) {
120 rettime = ktime_get();
121 delta = ktime_sub(rettime, calltime);
122 printk(KERN_DEBUG "initcall %lli_%pF returned 0 after %lld usecs\n",
123 (long long)entry->cookie,
125 (long long)ktime_to_ns(delta) >> 10);
128 /* 2) remove self from the pending queues */
129 spin_lock_irqsave(&async_lock, flags);
130 list_del(&entry->list);
131 if (domain->registered && list_empty(&domain->pending))
132 list_del_init(&domain->node);
134 /* 3) free the entry */
136 atomic_dec(&entry_count);
138 spin_unlock_irqrestore(&async_lock, flags);
140 /* 4) wake up any waiters */
141 wake_up(&async_done);
144 static async_cookie_t __async_schedule(async_func_ptr *ptr, void *data, struct async_domain *domain)
146 struct async_entry *entry;
148 async_cookie_t newcookie;
150 /* allow irq-off callers */
151 entry = kzalloc(sizeof(struct async_entry), GFP_ATOMIC);
154 * If we're out of memory or if there's too much work
155 * pending already, we execute synchronously.
157 if (!entry || atomic_read(&entry_count) > MAX_WORK) {
159 spin_lock_irqsave(&async_lock, flags);
160 newcookie = next_cookie++;
161 spin_unlock_irqrestore(&async_lock, flags);
163 /* low on memory.. run synchronously */
164 ptr(data, newcookie);
167 INIT_WORK(&entry->work, async_run_entry_fn);
170 entry->domain = domain;
172 spin_lock_irqsave(&async_lock, flags);
173 newcookie = entry->cookie = next_cookie++;
174 if (domain->registered && list_empty(&domain->pending))
175 list_add_tail(&domain->node, &async_domains);
176 list_add_tail(&entry->list, &domain->pending);
177 atomic_inc(&entry_count);
178 spin_unlock_irqrestore(&async_lock, flags);
180 /* mark that this task has queued an async job, used by module init */
181 current->flags |= PF_USED_ASYNC;
183 /* schedule for execution */
184 queue_work(system_unbound_wq, &entry->work);
190 * async_schedule - schedule a function for asynchronous execution
191 * @ptr: function to execute asynchronously
192 * @data: data pointer to pass to the function
194 * Returns an async_cookie_t that may be used for checkpointing later.
195 * Note: This function may be called from atomic or non-atomic contexts.
197 async_cookie_t async_schedule(async_func_ptr *ptr, void *data)
199 return __async_schedule(ptr, data, &async_dfl_domain);
201 EXPORT_SYMBOL_GPL(async_schedule);
204 * async_schedule_domain - schedule a function for asynchronous execution within a certain domain
205 * @ptr: function to execute asynchronously
206 * @data: data pointer to pass to the function
207 * @domain: the domain
209 * Returns an async_cookie_t that may be used for checkpointing later.
210 * @domain may be used in the async_synchronize_*_domain() functions to
211 * wait within a certain synchronization domain rather than globally. A
212 * synchronization domain is specified via @domain. Note: This function
213 * may be called from atomic or non-atomic contexts.
215 async_cookie_t async_schedule_domain(async_func_ptr *ptr, void *data,
216 struct async_domain *domain)
218 return __async_schedule(ptr, data, domain);
220 EXPORT_SYMBOL_GPL(async_schedule_domain);
223 * async_synchronize_full - synchronize all asynchronous function calls
225 * This function waits until all asynchronous function calls have been done.
227 void async_synchronize_full(void)
229 mutex_lock(&async_register_mutex);
231 struct async_domain *domain = NULL;
233 spin_lock_irq(&async_lock);
234 if (!list_empty(&async_domains))
235 domain = list_first_entry(&async_domains, typeof(*domain), node);
236 spin_unlock_irq(&async_lock);
238 async_synchronize_cookie_domain(ASYNC_COOKIE_MAX, domain);
239 } while (!list_empty(&async_domains));
240 mutex_unlock(&async_register_mutex);
242 EXPORT_SYMBOL_GPL(async_synchronize_full);
245 * async_unregister_domain - ensure no more anonymous waiters on this domain
246 * @domain: idle domain to flush out of any async_synchronize_full instances
248 * async_synchronize_{cookie|full}_domain() are not flushed since callers
249 * of these routines should know the lifetime of @domain
251 * Prefer ASYNC_DOMAIN_EXCLUSIVE() declarations over flushing
253 void async_unregister_domain(struct async_domain *domain)
255 mutex_lock(&async_register_mutex);
256 spin_lock_irq(&async_lock);
257 WARN_ON(!domain->registered || !list_empty(&domain->node) ||
258 !list_empty(&domain->pending));
259 domain->registered = 0;
260 spin_unlock_irq(&async_lock);
261 mutex_unlock(&async_register_mutex);
263 EXPORT_SYMBOL_GPL(async_unregister_domain);
266 * async_synchronize_full_domain - synchronize all asynchronous function within a certain domain
267 * @domain: the domain to synchronize
269 * This function waits until all asynchronous function calls for the
270 * synchronization domain specified by @domain have been done.
272 void async_synchronize_full_domain(struct async_domain *domain)
274 async_synchronize_cookie_domain(ASYNC_COOKIE_MAX, domain);
276 EXPORT_SYMBOL_GPL(async_synchronize_full_domain);
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
283 * This function waits until all asynchronous function calls for the
284 * synchronization domain specified by @domain submitted prior to @cookie
287 void async_synchronize_cookie_domain(async_cookie_t cookie, struct async_domain *domain)
289 ktime_t uninitialized_var(starttime), delta, endtime;
294 if (initcall_debug && system_state == SYSTEM_BOOTING) {
295 printk(KERN_DEBUG "async_waiting @ %i\n", task_pid_nr(current));
296 starttime = ktime_get();
299 wait_event(async_done, lowest_in_progress(domain) >= cookie);
301 if (initcall_debug && system_state == SYSTEM_BOOTING) {
302 endtime = ktime_get();
303 delta = ktime_sub(endtime, starttime);
305 printk(KERN_DEBUG "async_continuing @ %i after %lli usec\n",
306 task_pid_nr(current),
307 (long long)ktime_to_ns(delta) >> 10);
310 EXPORT_SYMBOL_GPL(async_synchronize_cookie_domain);
313 * async_synchronize_cookie - synchronize asynchronous function calls with cookie checkpointing
314 * @cookie: async_cookie_t to use as checkpoint
316 * This function waits until all asynchronous function calls prior to @cookie
319 void async_synchronize_cookie(async_cookie_t cookie)
321 async_synchronize_cookie_domain(cookie, &async_dfl_domain);
323 EXPORT_SYMBOL_GPL(async_synchronize_cookie);
326 * current_is_async - is %current an async worker task?
328 * Returns %true if %current is an async worker task.
330 bool current_is_async(void)
332 struct worker *worker = current_wq_worker();
334 return worker && worker->current_func == async_run_entry_fn;