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/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>
59 static async_cookie_t next_cookie = 1;
61 #define MAX_WORK 32768
63 static LIST_HEAD(async_pending);
64 static LIST_HEAD(async_running);
65 static DEFINE_SPINLOCK(async_lock);
68 struct list_head list;
69 struct work_struct work;
70 async_cookie_t cookie;
73 struct list_head *running;
76 static DECLARE_WAIT_QUEUE_HEAD(async_done);
78 static atomic_t entry_count;
80 extern int initcall_debug;
84 * MUST be called with the lock held!
86 static async_cookie_t __lowest_in_progress(struct list_head *running)
88 struct async_entry *entry;
90 if (!running) { /* just check the entry count */
91 if (atomic_read(&entry_count))
92 return 0; /* smaller than any cookie */
97 if (!list_empty(running)) {
98 entry = list_first_entry(running,
99 struct async_entry, list);
100 return entry->cookie;
103 list_for_each_entry(entry, &async_pending, list)
104 if (entry->running == running)
105 return entry->cookie;
107 return next_cookie; /* "infinity" value */
110 static async_cookie_t lowest_in_progress(struct list_head *running)
115 spin_lock_irqsave(&async_lock, flags);
116 ret = __lowest_in_progress(running);
117 spin_unlock_irqrestore(&async_lock, flags);
122 * pick the first pending entry and run it
124 static void async_run_entry_fn(struct work_struct *work)
126 struct async_entry *entry =
127 container_of(work, struct async_entry, work);
129 ktime_t calltime, delta, rettime;
131 /* 1) move self to the running queue */
132 spin_lock_irqsave(&async_lock, flags);
133 list_move_tail(&entry->list, entry->running);
134 spin_unlock_irqrestore(&async_lock, flags);
136 /* 2) run (and print duration) */
137 if (initcall_debug && system_state == SYSTEM_BOOTING) {
138 printk("calling %lli_%pF @ %i\n", (long long)entry->cookie,
139 entry->func, task_pid_nr(current));
140 calltime = ktime_get();
142 entry->func(entry->data, entry->cookie);
143 if (initcall_debug && system_state == SYSTEM_BOOTING) {
144 rettime = ktime_get();
145 delta = ktime_sub(rettime, calltime);
146 printk("initcall %lli_%pF returned 0 after %lld usecs\n",
147 (long long)entry->cookie,
149 (long long)ktime_to_ns(delta) >> 10);
152 /* 3) remove self from the running queue */
153 spin_lock_irqsave(&async_lock, flags);
154 list_del(&entry->list);
156 /* 4) free the entry */
158 atomic_dec(&entry_count);
160 spin_unlock_irqrestore(&async_lock, flags);
162 /* 5) wake up any waiters */
163 wake_up(&async_done);
166 static async_cookie_t __async_schedule(async_func_ptr *ptr, void *data, struct list_head *running)
168 struct async_entry *entry;
170 async_cookie_t newcookie;
172 /* allow irq-off callers */
173 entry = kzalloc(sizeof(struct async_entry), GFP_ATOMIC);
176 * If we're out of memory or if there's too much work
177 * pending already, we execute synchronously.
179 if (!entry || atomic_read(&entry_count) > MAX_WORK) {
181 spin_lock_irqsave(&async_lock, flags);
182 newcookie = next_cookie++;
183 spin_unlock_irqrestore(&async_lock, flags);
185 /* low on memory.. run synchronously */
186 ptr(data, newcookie);
189 INIT_WORK(&entry->work, async_run_entry_fn);
192 entry->running = running;
194 spin_lock_irqsave(&async_lock, flags);
195 newcookie = entry->cookie = next_cookie++;
196 list_add_tail(&entry->list, &async_pending);
197 atomic_inc(&entry_count);
198 spin_unlock_irqrestore(&async_lock, flags);
200 /* schedule for execution */
201 queue_work(system_unbound_wq, &entry->work);
207 * async_schedule - schedule a function for asynchronous execution
208 * @ptr: function to execute asynchronously
209 * @data: data pointer to pass to the function
211 * Returns an async_cookie_t that may be used for checkpointing later.
212 * Note: This function may be called from atomic or non-atomic contexts.
214 async_cookie_t async_schedule(async_func_ptr *ptr, void *data)
216 return __async_schedule(ptr, data, &async_running);
218 EXPORT_SYMBOL_GPL(async_schedule);
221 * async_schedule_domain - schedule a function for asynchronous execution within a certain domain
222 * @ptr: function to execute asynchronously
223 * @data: data pointer to pass to the function
224 * @running: running list for the domain
226 * Returns an async_cookie_t that may be used for checkpointing later.
227 * @running may be used in the async_synchronize_*_domain() functions
228 * to wait within a certain synchronization domain rather than globally.
229 * A synchronization domain is specified via the running queue @running to use.
230 * Note: This function may be called from atomic or non-atomic contexts.
232 async_cookie_t async_schedule_domain(async_func_ptr *ptr, void *data,
233 struct list_head *running)
235 return __async_schedule(ptr, data, running);
237 EXPORT_SYMBOL_GPL(async_schedule_domain);
240 * async_synchronize_full - synchronize all asynchronous function calls
242 * This function waits until all asynchronous function calls have been done.
244 void async_synchronize_full(void)
246 async_synchronize_cookie_domain(next_cookie, NULL);
248 EXPORT_SYMBOL_GPL(async_synchronize_full);
251 * async_synchronize_full_domain - synchronize all asynchronous function within a certain domain
252 * @list: running list to synchronize on
254 * This function waits until all asynchronous function calls for the
255 * synchronization domain specified by the running list @list have been done.
257 void async_synchronize_full_domain(struct list_head *list)
259 async_synchronize_cookie_domain(next_cookie, list);
261 EXPORT_SYMBOL_GPL(async_synchronize_full_domain);
264 * async_synchronize_cookie_domain - synchronize asynchronous function calls within a certain domain with cookie checkpointing
265 * @cookie: async_cookie_t to use as checkpoint
266 * @running: running list to synchronize on, NULL indicates all lists
268 * This function waits until all asynchronous function calls for the
269 * synchronization domain specified by the running list @list submitted
270 * prior to @cookie have been done.
272 void async_synchronize_cookie_domain(async_cookie_t cookie,
273 struct list_head *running)
275 ktime_t starttime, delta, endtime;
277 if (initcall_debug && system_state == SYSTEM_BOOTING) {
278 printk("async_waiting @ %i\n", task_pid_nr(current));
279 starttime = ktime_get();
282 wait_event(async_done, lowest_in_progress(running) >= cookie);
284 if (initcall_debug && system_state == SYSTEM_BOOTING) {
285 endtime = ktime_get();
286 delta = ktime_sub(endtime, starttime);
288 printk("async_continuing @ %i after %lli usec\n",
289 task_pid_nr(current),
290 (long long)ktime_to_ns(delta) >> 10);
293 EXPORT_SYMBOL_GPL(async_synchronize_cookie_domain);
296 * async_synchronize_cookie - synchronize asynchronous function calls with cookie checkpointing
297 * @cookie: async_cookie_t to use as checkpoint
299 * This function waits until all asynchronous function calls prior to @cookie
302 void async_synchronize_cookie(async_cookie_t cookie)
304 async_synchronize_cookie_domain(cookie, &async_running);
306 EXPORT_SYMBOL_GPL(async_synchronize_cookie);