async: Fix running list handling.
[linux-3.10.git] / kernel / async.c
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/module.h>
53 #include <linux/wait.h>
54 #include <linux/sched.h>
55 #include <linux/init.h>
56 #include <linux/kthread.h>
57 #include <asm/atomic.h>
58
59 static async_cookie_t next_cookie = 1;
60
61 #define MAX_THREADS     256
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 static int async_enabled = 0;
69
70 struct async_entry {
71         struct list_head list;
72         async_cookie_t   cookie;
73         async_func_ptr   *func;
74         void             *data;
75         struct list_head *running;
76 };
77
78 static DECLARE_WAIT_QUEUE_HEAD(async_done);
79 static DECLARE_WAIT_QUEUE_HEAD(async_new);
80
81 static atomic_t entry_count;
82 static atomic_t thread_count;
83
84 extern int initcall_debug;
85
86
87 /*
88  * MUST be called with the lock held!
89  */
90 static async_cookie_t  __lowest_in_progress(struct list_head *running)
91 {
92         struct async_entry *entry;
93         if (!list_empty(running)) {
94                 entry = list_first_entry(running,
95                         struct async_entry, list);
96                 return entry->cookie;
97         } else if (!list_empty(&async_pending)) {
98                 entry = list_first_entry(&async_pending,
99                         struct async_entry, list);
100                 return entry->cookie;
101         } else {
102                 /* nothing in progress... next_cookie is "infinity" */
103                 return next_cookie;
104         }
105
106 }
107
108 static async_cookie_t  lowest_in_progress(struct list_head *running)
109 {
110         unsigned long flags;
111         async_cookie_t ret;
112
113         spin_lock_irqsave(&async_lock, flags);
114         ret = __lowest_in_progress(running);
115         spin_unlock_irqrestore(&async_lock, flags);
116         return ret;
117 }
118 /*
119  * pick the first pending entry and run it
120  */
121 static void run_one_entry(void)
122 {
123         unsigned long flags;
124         struct async_entry *entry;
125         ktime_t calltime, delta, rettime;
126
127         /* 1) pick one task from the pending queue */
128
129         spin_lock_irqsave(&async_lock, flags);
130         if (list_empty(&async_pending))
131                 goto out;
132         entry = list_first_entry(&async_pending, struct async_entry, list);
133
134         /* 2) move it to the running queue */
135         list_del(&entry->list);
136         list_add_tail(&entry->list, entry->running);
137         spin_unlock_irqrestore(&async_lock, flags);
138
139         /* 3) run it (and print duration)*/
140         if (initcall_debug && system_state == SYSTEM_BOOTING) {
141                 printk("calling  %lli_%pF @ %i\n", (long long)entry->cookie,
142                         entry->func, task_pid_nr(current));
143                 calltime = ktime_get();
144         }
145         entry->func(entry->data, entry->cookie);
146         if (initcall_debug && system_state == SYSTEM_BOOTING) {
147                 rettime = ktime_get();
148                 delta = ktime_sub(rettime, calltime);
149                 printk("initcall %lli_%pF returned 0 after %lld usecs\n",
150                         (long long)entry->cookie,
151                         entry->func,
152                         (long long)ktime_to_ns(delta) >> 10);
153         }
154
155         /* 4) remove it from the running queue */
156         spin_lock_irqsave(&async_lock, flags);
157         list_del(&entry->list);
158
159         /* 5) free the entry  */
160         kfree(entry);
161         atomic_dec(&entry_count);
162
163         spin_unlock_irqrestore(&async_lock, flags);
164
165         /* 6) wake up any waiters. */
166         wake_up(&async_done);
167         return;
168
169 out:
170         spin_unlock_irqrestore(&async_lock, flags);
171 }
172
173
174 static async_cookie_t __async_schedule(async_func_ptr *ptr, void *data, struct list_head *running)
175 {
176         struct async_entry *entry;
177         unsigned long flags;
178         async_cookie_t newcookie;
179         
180
181         /* allow irq-off callers */
182         entry = kzalloc(sizeof(struct async_entry), GFP_ATOMIC);
183
184         /*
185          * If we're out of memory or if there's too much work
186          * pending already, we execute synchronously.
187          */
188         if (!async_enabled || !entry || atomic_read(&entry_count) > MAX_WORK) {
189                 kfree(entry);
190                 spin_lock_irqsave(&async_lock, flags);
191                 newcookie = next_cookie++;
192                 spin_unlock_irqrestore(&async_lock, flags);
193
194                 /* low on memory.. run synchronously */
195                 ptr(data, newcookie);
196                 return newcookie;
197         }
198         entry->func = ptr;
199         entry->data = data;
200         entry->running = running;
201
202         spin_lock_irqsave(&async_lock, flags);
203         newcookie = entry->cookie = next_cookie++;
204         list_add_tail(&entry->list, &async_pending);
205         atomic_inc(&entry_count);
206         spin_unlock_irqrestore(&async_lock, flags);
207         wake_up(&async_new);
208         return newcookie;
209 }
210
211 async_cookie_t async_schedule(async_func_ptr *ptr, void *data)
212 {
213         return __async_schedule(ptr, data, &async_running);
214 }
215 EXPORT_SYMBOL_GPL(async_schedule);
216
217 async_cookie_t async_schedule_special(async_func_ptr *ptr, void *data, struct list_head *running)
218 {
219         return __async_schedule(ptr, data, running);
220 }
221 EXPORT_SYMBOL_GPL(async_schedule_special);
222
223 void async_synchronize_full(void)
224 {
225         do {
226                 async_synchronize_cookie(next_cookie);
227         } while (!list_empty(&async_running) || !list_empty(&async_pending));
228 }
229 EXPORT_SYMBOL_GPL(async_synchronize_full);
230
231 void async_synchronize_full_special(struct list_head *list)
232 {
233         async_synchronize_cookie_special(next_cookie, list);
234 }
235 EXPORT_SYMBOL_GPL(async_synchronize_full_special);
236
237 void async_synchronize_cookie_special(async_cookie_t cookie, struct list_head *running)
238 {
239         ktime_t starttime, delta, endtime;
240
241         if (initcall_debug && system_state == SYSTEM_BOOTING) {
242                 printk("async_waiting @ %i\n", task_pid_nr(current));
243                 starttime = ktime_get();
244         }
245
246         wait_event(async_done, lowest_in_progress(running) >= cookie);
247
248         if (initcall_debug && system_state == SYSTEM_BOOTING) {
249                 endtime = ktime_get();
250                 delta = ktime_sub(endtime, starttime);
251
252                 printk("async_continuing @ %i after %lli usec\n",
253                         task_pid_nr(current),
254                         (long long)ktime_to_ns(delta) >> 10);
255         }
256 }
257 EXPORT_SYMBOL_GPL(async_synchronize_cookie_special);
258
259 void async_synchronize_cookie(async_cookie_t cookie)
260 {
261         async_synchronize_cookie_special(cookie, &async_running);
262 }
263 EXPORT_SYMBOL_GPL(async_synchronize_cookie);
264
265
266 static int async_thread(void *unused)
267 {
268         DECLARE_WAITQUEUE(wq, current);
269         add_wait_queue(&async_new, &wq);
270
271         while (!kthread_should_stop()) {
272                 int ret = HZ;
273                 set_current_state(TASK_INTERRUPTIBLE);
274                 /*
275                  * check the list head without lock.. false positives
276                  * are dealt with inside run_one_entry() while holding
277                  * the lock.
278                  */
279                 rmb();
280                 if (!list_empty(&async_pending))
281                         run_one_entry();
282                 else
283                         ret = schedule_timeout(HZ);
284
285                 if (ret == 0) {
286                         /*
287                          * we timed out, this means we as thread are redundant.
288                          * we sign off and die, but we to avoid any races there
289                          * is a last-straw check to see if work snuck in.
290                          */
291                         atomic_dec(&thread_count);
292                         wmb(); /* manager must see our departure first */
293                         if (list_empty(&async_pending))
294                                 break;
295                         /*
296                          * woops work came in between us timing out and us
297                          * signing off; we need to stay alive and keep working.
298                          */
299                         atomic_inc(&thread_count);
300                 }
301         }
302         remove_wait_queue(&async_new, &wq);
303
304         return 0;
305 }
306
307 static int async_manager_thread(void *unused)
308 {
309         DECLARE_WAITQUEUE(wq, current);
310         add_wait_queue(&async_new, &wq);
311
312         while (!kthread_should_stop()) {
313                 int tc, ec;
314
315                 set_current_state(TASK_INTERRUPTIBLE);
316
317                 tc = atomic_read(&thread_count);
318                 rmb();
319                 ec = atomic_read(&entry_count);
320
321                 while (tc < ec && tc < MAX_THREADS) {
322                         kthread_run(async_thread, NULL, "async/%i", tc);
323                         atomic_inc(&thread_count);
324                         tc++;
325                 }
326
327                 schedule();
328         }
329         remove_wait_queue(&async_new, &wq);
330
331         return 0;
332 }
333
334 static int __init async_init(void)
335 {
336         if (async_enabled)
337                 kthread_run(async_manager_thread, NULL, "async/mgr");
338         return 0;
339 }
340
341 static int __init setup_async(char *str)
342 {
343         async_enabled = 1;
344         return 1;
345 }
346
347 __setup("fastboot", setup_async);
348
349
350 core_initcall(async_init);