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 static async_cookie_t next_cookie = 1;
61
62 #define MAX_WORK 32768
63
64 static LIST_HEAD(async_pending);
65 static LIST_HEAD(async_running);
66 static DEFINE_SPINLOCK(async_lock);
67
68 struct async_entry {
69 struct list_head list;
70 struct work_struct work;
71 async_cookie_t cookie;
72 async_func_ptr *func;
73 void *data;
74 struct list_head *running;
75 };
76
77 static DECLARE_WAIT_QUEUE_HEAD(async_done);
78
79 static atomic_t entry_count;
80
81
82 /*
83 * MUST be called with the lock held!
84 */
__lowest_in_progress(struct list_head * running)85 static async_cookie_t __lowest_in_progress(struct list_head *running)
86 {
87 struct async_entry *entry;
88
89 if (!running) { /* just check the entry count */
90 if (atomic_read(&entry_count))
91 return 0; /* smaller than any cookie */
92 else
93 return next_cookie;
94 }
95
96 if (!list_empty(running)) {
97 entry = list_first_entry(running,
98 struct async_entry, list);
99 return entry->cookie;
100 }
101
102 list_for_each_entry(entry, &async_pending, list)
103 if (entry->running == running)
104 return entry->cookie;
105
106 return next_cookie; /* "infinity" value */
107 }
108
lowest_in_progress(struct list_head * running)109 static async_cookie_t lowest_in_progress(struct list_head *running)
110 {
111 unsigned long flags;
112 async_cookie_t ret;
113
114 spin_lock_irqsave(&async_lock, flags);
115 ret = __lowest_in_progress(running);
116 spin_unlock_irqrestore(&async_lock, flags);
117 return ret;
118 }
119
120 /*
121 * pick the first pending entry and run it
122 */
async_run_entry_fn(struct work_struct * work)123 static void async_run_entry_fn(struct work_struct *work)
124 {
125 struct async_entry *entry =
126 container_of(work, struct async_entry, work);
127 unsigned long flags;
128 ktime_t uninitialized_var(calltime), delta, rettime;
129
130 /* 1) move self to the running queue */
131 spin_lock_irqsave(&async_lock, flags);
132 list_move_tail(&entry->list, entry->running);
133 spin_unlock_irqrestore(&async_lock, flags);
134
135 /* 2) run (and print duration) */
136 if (initcall_debug && system_state == SYSTEM_BOOTING) {
137 printk(KERN_DEBUG "calling %lli_%pF @ %i\n",
138 (long long)entry->cookie,
139 entry->func, task_pid_nr(current));
140 calltime = ktime_get();
141 }
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(KERN_DEBUG "initcall %lli_%pF returned 0 after %lld usecs\n",
147 (long long)entry->cookie,
148 entry->func,
149 (long long)ktime_to_ns(delta) >> 10);
150 }
151
152 /* 3) remove self from the running queue */
153 spin_lock_irqsave(&async_lock, flags);
154 list_del(&entry->list);
155
156 /* 4) free the entry */
157 kfree(entry);
158 atomic_dec(&entry_count);
159
160 spin_unlock_irqrestore(&async_lock, flags);
161
162 /* 5) wake up any waiters */
163 wake_up(&async_done);
164 }
165
__async_schedule(async_func_ptr * ptr,void * data,struct list_head * running)166 static async_cookie_t __async_schedule(async_func_ptr *ptr, void *data, struct list_head *running)
167 {
168 struct async_entry *entry;
169 unsigned long flags;
170 async_cookie_t newcookie;
171
172 /* allow irq-off callers */
173 entry = kzalloc(sizeof(struct async_entry), GFP_ATOMIC);
174
175 /*
176 * If we're out of memory or if there's too much work
177 * pending already, we execute synchronously.
178 */
179 if (!entry || atomic_read(&entry_count) > MAX_WORK) {
180 kfree(entry);
181 spin_lock_irqsave(&async_lock, flags);
182 newcookie = next_cookie++;
183 spin_unlock_irqrestore(&async_lock, flags);
184
185 /* low on memory.. run synchronously */
186 ptr(data, newcookie);
187 return newcookie;
188 }
189 INIT_WORK(&entry->work, async_run_entry_fn);
190 entry->func = ptr;
191 entry->data = data;
192 entry->running = running;
193
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);
199
200 /* schedule for execution */
201 queue_work(system_unbound_wq, &entry->work);
202
203 return newcookie;
204 }
205
206 /**
207 * async_schedule - schedule a function for asynchronous execution
208 * @ptr: function to execute asynchronously
209 * @data: data pointer to pass to the function
210 *
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.
213 */
async_schedule(async_func_ptr * ptr,void * data)214 async_cookie_t async_schedule(async_func_ptr *ptr, void *data)
215 {
216 return __async_schedule(ptr, data, &async_running);
217 }
218 EXPORT_SYMBOL_GPL(async_schedule);
219
220 /**
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
225 *
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.
231 */
async_schedule_domain(async_func_ptr * ptr,void * data,struct list_head * running)232 async_cookie_t async_schedule_domain(async_func_ptr *ptr, void *data,
233 struct list_head *running)
234 {
235 return __async_schedule(ptr, data, running);
236 }
237 EXPORT_SYMBOL_GPL(async_schedule_domain);
238
239 /**
240 * async_synchronize_full - synchronize all asynchronous function calls
241 *
242 * This function waits until all asynchronous function calls have been done.
243 */
async_synchronize_full(void)244 void async_synchronize_full(void)
245 {
246 async_synchronize_cookie_domain(next_cookie, NULL);
247 }
248 EXPORT_SYMBOL_GPL(async_synchronize_full);
249
250 /**
251 * async_synchronize_full_domain - synchronize all asynchronous function within a certain domain
252 * @list: running list to synchronize on
253 *
254 * This function waits until all asynchronous function calls for the
255 * synchronization domain specified by the running list @list have been done.
256 */
async_synchronize_full_domain(struct list_head * list)257 void async_synchronize_full_domain(struct list_head *list)
258 {
259 async_synchronize_cookie_domain(next_cookie, list);
260 }
261 EXPORT_SYMBOL_GPL(async_synchronize_full_domain);
262
263 /**
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
267 *
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.
271 */
async_synchronize_cookie_domain(async_cookie_t cookie,struct list_head * running)272 void async_synchronize_cookie_domain(async_cookie_t cookie,
273 struct list_head *running)
274 {
275 ktime_t uninitialized_var(starttime), delta, endtime;
276
277 if (initcall_debug && system_state == SYSTEM_BOOTING) {
278 printk(KERN_DEBUG "async_waiting @ %i\n", task_pid_nr(current));
279 starttime = ktime_get();
280 }
281
282 wait_event(async_done, lowest_in_progress(running) >= cookie);
283
284 if (initcall_debug && system_state == SYSTEM_BOOTING) {
285 endtime = ktime_get();
286 delta = ktime_sub(endtime, starttime);
287
288 printk(KERN_DEBUG "async_continuing @ %i after %lli usec\n",
289 task_pid_nr(current),
290 (long long)ktime_to_ns(delta) >> 10);
291 }
292 }
293 EXPORT_SYMBOL_GPL(async_synchronize_cookie_domain);
294
295 /**
296 * async_synchronize_cookie - synchronize asynchronous function calls with cookie checkpointing
297 * @cookie: async_cookie_t to use as checkpoint
298 *
299 * This function waits until all asynchronous function calls prior to @cookie
300 * have been done.
301 */
async_synchronize_cookie(async_cookie_t cookie)302 void async_synchronize_cookie(async_cookie_t cookie)
303 {
304 async_synchronize_cookie_domain(cookie, &async_running);
305 }
306 EXPORT_SYMBOL_GPL(async_synchronize_cookie);
307