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Arjan van de Ven22a9d642009-01-07 08:45:46 -08001/*
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
16Goals and Theory of Operation
17
18The primary goal of this feature is to reduce the kernel boot time,
19by doing various independent hardware delays and discovery operations
20decoupled and not strictly serialized.
21
22More specifically, the asynchronous function call concept allows
23certain operations (primarily during system boot) to happen
24asynchronously, out of order, while these operations still
25have their externally visible parts happen sequentially and in-order.
26(not unlike how out-of-order CPUs retire their instructions in order)
27
28Key to the asynchronous function call implementation is the concept of
29a "sequence cookie" (which, although it has an abstracted type, can be
30thought of as a monotonically incrementing number).
31
32The async core will assign each scheduled event such a sequence cookie and
33pass this to the called functions.
34
35The asynchronously called function should before doing a globally visible
36operation, such as registering device numbers, call the
37async_synchronize_cookie() function and pass in its own cookie. The
38async_synchronize_cookie() function will make sure that all asynchronous
39operations that were scheduled prior to the operation corresponding with the
40cookie have completed.
41
42Subsystem/driver initialization code that scheduled asynchronous probe
43functions, but which shares global resources with other drivers/subsystems
44that do not use the asynchronous call feature, need to do a full
45synchronization with the async_synchronize_full() function, before returning
46from their init function. This is to maintain strict ordering between the
47asynchronous and synchronous parts of the kernel.
48
49*/
50
51#include <linux/async.h>
Arjan van de Ven97107942009-03-15 11:11:44 -070052#include <linux/bug.h>
Arjan van de Ven22a9d642009-01-07 08:45:46 -080053#include <linux/module.h>
54#include <linux/wait.h>
55#include <linux/sched.h>
56#include <linux/init.h>
57#include <linux/kthread.h>
Cornelia Huck86532d82009-01-19 13:45:31 +010058#include <linux/delay.h>
Arjan van de Ven22a9d642009-01-07 08:45:46 -080059#include <asm/atomic.h>
60
61static async_cookie_t next_cookie = 1;
62
63#define MAX_THREADS 256
64#define MAX_WORK 32768
65
66static LIST_HEAD(async_pending);
67static LIST_HEAD(async_running);
68static DEFINE_SPINLOCK(async_lock);
69
Arjan van de Vencdb80f62009-01-09 13:23:45 -080070static int async_enabled = 0;
71
Arjan van de Ven22a9d642009-01-07 08:45:46 -080072struct async_entry {
73 struct list_head list;
74 async_cookie_t cookie;
75 async_func_ptr *func;
76 void *data;
77 struct list_head *running;
78};
79
80static DECLARE_WAIT_QUEUE_HEAD(async_done);
81static DECLARE_WAIT_QUEUE_HEAD(async_new);
82
83static atomic_t entry_count;
84static atomic_t thread_count;
85
86extern int initcall_debug;
87
88
89/*
90 * MUST be called with the lock held!
91 */
92static async_cookie_t __lowest_in_progress(struct list_head *running)
93{
94 struct async_entry *entry;
James Bottomleyd5a877e2009-05-24 13:03:43 -070095
Arjan van de Ven37a76bd2009-01-11 15:35:01 +000096 if (!list_empty(running)) {
97 entry = list_first_entry(running,
Arjan van de Ven22a9d642009-01-07 08:45:46 -080098 struct async_entry, list);
Linus Torvalds3af968e2009-06-08 12:31:53 -070099 return entry->cookie;
Arjan van de Ven22a9d642009-01-07 08:45:46 -0800100 }
101
Linus Torvalds3af968e2009-06-08 12:31:53 -0700102 list_for_each_entry(entry, &async_pending, list)
103 if (entry->running == running)
104 return entry->cookie;
James Bottomleyd5a877e2009-05-24 13:03:43 -0700105
Linus Torvalds3af968e2009-06-08 12:31:53 -0700106 return next_cookie; /* "infinity" value */
Arjan van de Ven22a9d642009-01-07 08:45:46 -0800107}
Arjan van de Ven37a76bd2009-01-11 15:35:01 +0000108
109static 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}
Arjan van de Ven22a9d642009-01-07 08:45:46 -0800119/*
120 * pick the first pending entry and run it
121 */
122static void run_one_entry(void)
123{
124 unsigned long flags;
125 struct async_entry *entry;
126 ktime_t calltime, delta, rettime;
127
128 /* 1) pick one task from the pending queue */
129
130 spin_lock_irqsave(&async_lock, flags);
131 if (list_empty(&async_pending))
132 goto out;
133 entry = list_first_entry(&async_pending, struct async_entry, list);
134
135 /* 2) move it to the running queue */
Stefan Richterf7de7621f2009-02-02 13:24:34 +0100136 list_move_tail(&entry->list, entry->running);
Arjan van de Ven22a9d642009-01-07 08:45:46 -0800137 spin_unlock_irqrestore(&async_lock, flags);
138
139 /* 3) run it (and print duration)*/
Arjan van de Venad160d22009-01-07 09:28:53 -0800140 if (initcall_debug && system_state == SYSTEM_BOOTING) {
Andrew Morton58763a22009-02-04 15:11:58 -0800141 printk("calling %lli_%pF @ %i\n", (long long)entry->cookie,
142 entry->func, task_pid_nr(current));
Arjan van de Ven22a9d642009-01-07 08:45:46 -0800143 calltime = ktime_get();
144 }
145 entry->func(entry->data, entry->cookie);
Arjan van de Venad160d22009-01-07 09:28:53 -0800146 if (initcall_debug && system_state == SYSTEM_BOOTING) {
Arjan van de Ven22a9d642009-01-07 08:45:46 -0800147 rettime = ktime_get();
148 delta = ktime_sub(rettime, calltime);
Andrew Morton58763a22009-02-04 15:11:58 -0800149 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);
Arjan van de Ven22a9d642009-01-07 08:45:46 -0800153 }
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
169out:
170 spin_unlock_irqrestore(&async_lock, flags);
171}
172
173
174static 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 */
Arjan van de Vencdb80f62009-01-09 13:23:45 -0800188 if (!async_enabled || !entry || atomic_read(&entry_count) > MAX_WORK) {
Arjan van de Ven22a9d642009-01-07 08:45:46 -0800189 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
Cornelia Huckf30d5b32009-01-19 13:45:33 +0100211/**
212 * async_schedule - schedule a function for asynchronous execution
213 * @ptr: function to execute asynchronously
214 * @data: data pointer to pass to the function
215 *
216 * Returns an async_cookie_t that may be used for checkpointing later.
217 * Note: This function may be called from atomic or non-atomic contexts.
218 */
Arjan van de Ven22a9d642009-01-07 08:45:46 -0800219async_cookie_t async_schedule(async_func_ptr *ptr, void *data)
220{
Cornelia Huck7a89bbc2009-01-19 13:45:28 +0100221 return __async_schedule(ptr, data, &async_running);
Arjan van de Ven22a9d642009-01-07 08:45:46 -0800222}
223EXPORT_SYMBOL_GPL(async_schedule);
224
Cornelia Huckf30d5b32009-01-19 13:45:33 +0100225/**
Cornelia Huck766ccb92009-01-20 15:31:31 +0100226 * async_schedule_domain - schedule a function for asynchronous execution within a certain domain
Cornelia Huckf30d5b32009-01-19 13:45:33 +0100227 * @ptr: function to execute asynchronously
228 * @data: data pointer to pass to the function
Cornelia Huck766ccb92009-01-20 15:31:31 +0100229 * @running: running list for the domain
Cornelia Huckf30d5b32009-01-19 13:45:33 +0100230 *
231 * Returns an async_cookie_t that may be used for checkpointing later.
Cornelia Huck766ccb92009-01-20 15:31:31 +0100232 * @running may be used in the async_synchronize_*_domain() functions
233 * to wait within a certain synchronization domain rather than globally.
234 * A synchronization domain is specified via the running queue @running to use.
Cornelia Huckf30d5b32009-01-19 13:45:33 +0100235 * Note: This function may be called from atomic or non-atomic contexts.
236 */
Cornelia Huck766ccb92009-01-20 15:31:31 +0100237async_cookie_t async_schedule_domain(async_func_ptr *ptr, void *data,
238 struct list_head *running)
Arjan van de Ven22a9d642009-01-07 08:45:46 -0800239{
240 return __async_schedule(ptr, data, running);
241}
Cornelia Huck766ccb92009-01-20 15:31:31 +0100242EXPORT_SYMBOL_GPL(async_schedule_domain);
Arjan van de Ven22a9d642009-01-07 08:45:46 -0800243
Cornelia Huckf30d5b32009-01-19 13:45:33 +0100244/**
245 * async_synchronize_full - synchronize all asynchronous function calls
246 *
247 * This function waits until all asynchronous function calls have been done.
248 */
Arjan van de Ven22a9d642009-01-07 08:45:46 -0800249void async_synchronize_full(void)
250{
Arjan van de Ven33b04b92009-01-08 12:35:11 -0800251 do {
252 async_synchronize_cookie(next_cookie);
253 } while (!list_empty(&async_running) || !list_empty(&async_pending));
Arjan van de Ven22a9d642009-01-07 08:45:46 -0800254}
255EXPORT_SYMBOL_GPL(async_synchronize_full);
256
Cornelia Huckf30d5b32009-01-19 13:45:33 +0100257/**
Cornelia Huck766ccb92009-01-20 15:31:31 +0100258 * async_synchronize_full_domain - synchronize all asynchronous function within a certain domain
Cornelia Huckf30d5b32009-01-19 13:45:33 +0100259 * @list: running list to synchronize on
260 *
Cornelia Huck766ccb92009-01-20 15:31:31 +0100261 * This function waits until all asynchronous function calls for the
262 * synchronization domain specified by the running list @list have been done.
Cornelia Huckf30d5b32009-01-19 13:45:33 +0100263 */
Cornelia Huck766ccb92009-01-20 15:31:31 +0100264void async_synchronize_full_domain(struct list_head *list)
Arjan van de Ven22a9d642009-01-07 08:45:46 -0800265{
Cornelia Huck766ccb92009-01-20 15:31:31 +0100266 async_synchronize_cookie_domain(next_cookie, list);
Arjan van de Ven22a9d642009-01-07 08:45:46 -0800267}
Cornelia Huck766ccb92009-01-20 15:31:31 +0100268EXPORT_SYMBOL_GPL(async_synchronize_full_domain);
Arjan van de Ven22a9d642009-01-07 08:45:46 -0800269
Cornelia Huckf30d5b32009-01-19 13:45:33 +0100270/**
Cornelia Huck766ccb92009-01-20 15:31:31 +0100271 * async_synchronize_cookie_domain - synchronize asynchronous function calls within a certain domain with cookie checkpointing
Cornelia Huckf30d5b32009-01-19 13:45:33 +0100272 * @cookie: async_cookie_t to use as checkpoint
273 * @running: running list to synchronize on
274 *
Cornelia Huck766ccb92009-01-20 15:31:31 +0100275 * This function waits until all asynchronous function calls for the
276 * synchronization domain specified by the running list @list submitted
277 * prior to @cookie have been done.
Cornelia Huckf30d5b32009-01-19 13:45:33 +0100278 */
Cornelia Huck766ccb92009-01-20 15:31:31 +0100279void async_synchronize_cookie_domain(async_cookie_t cookie,
280 struct list_head *running)
Arjan van de Ven22a9d642009-01-07 08:45:46 -0800281{
282 ktime_t starttime, delta, endtime;
283
Arjan van de Venad160d22009-01-07 09:28:53 -0800284 if (initcall_debug && system_state == SYSTEM_BOOTING) {
Arjan van de Ven22a9d642009-01-07 08:45:46 -0800285 printk("async_waiting @ %i\n", task_pid_nr(current));
286 starttime = ktime_get();
287 }
288
Arjan van de Ven37a76bd2009-01-11 15:35:01 +0000289 wait_event(async_done, lowest_in_progress(running) >= cookie);
Arjan van de Ven22a9d642009-01-07 08:45:46 -0800290
Arjan van de Venad160d22009-01-07 09:28:53 -0800291 if (initcall_debug && system_state == SYSTEM_BOOTING) {
Arjan van de Ven22a9d642009-01-07 08:45:46 -0800292 endtime = ktime_get();
293 delta = ktime_sub(endtime, starttime);
294
295 printk("async_continuing @ %i after %lli usec\n",
Andrew Morton58763a22009-02-04 15:11:58 -0800296 task_pid_nr(current),
297 (long long)ktime_to_ns(delta) >> 10);
Arjan van de Ven22a9d642009-01-07 08:45:46 -0800298 }
299}
Cornelia Huck766ccb92009-01-20 15:31:31 +0100300EXPORT_SYMBOL_GPL(async_synchronize_cookie_domain);
Arjan van de Ven22a9d642009-01-07 08:45:46 -0800301
Cornelia Huckf30d5b32009-01-19 13:45:33 +0100302/**
303 * async_synchronize_cookie - synchronize asynchronous function calls with cookie checkpointing
304 * @cookie: async_cookie_t to use as checkpoint
305 *
306 * This function waits until all asynchronous function calls prior to @cookie
307 * have been done.
308 */
Arjan van de Ven22a9d642009-01-07 08:45:46 -0800309void async_synchronize_cookie(async_cookie_t cookie)
310{
Cornelia Huck766ccb92009-01-20 15:31:31 +0100311 async_synchronize_cookie_domain(cookie, &async_running);
Arjan van de Ven22a9d642009-01-07 08:45:46 -0800312}
313EXPORT_SYMBOL_GPL(async_synchronize_cookie);
314
315
316static int async_thread(void *unused)
317{
318 DECLARE_WAITQUEUE(wq, current);
319 add_wait_queue(&async_new, &wq);
320
321 while (!kthread_should_stop()) {
322 int ret = HZ;
323 set_current_state(TASK_INTERRUPTIBLE);
324 /*
325 * check the list head without lock.. false positives
326 * are dealt with inside run_one_entry() while holding
327 * the lock.
328 */
329 rmb();
330 if (!list_empty(&async_pending))
331 run_one_entry();
332 else
333 ret = schedule_timeout(HZ);
334
335 if (ret == 0) {
336 /*
337 * we timed out, this means we as thread are redundant.
338 * we sign off and die, but we to avoid any races there
339 * is a last-straw check to see if work snuck in.
340 */
341 atomic_dec(&thread_count);
342 wmb(); /* manager must see our departure first */
343 if (list_empty(&async_pending))
344 break;
345 /*
346 * woops work came in between us timing out and us
347 * signing off; we need to stay alive and keep working.
348 */
349 atomic_inc(&thread_count);
350 }
351 }
352 remove_wait_queue(&async_new, &wq);
353
354 return 0;
355}
356
357static int async_manager_thread(void *unused)
358{
359 DECLARE_WAITQUEUE(wq, current);
360 add_wait_queue(&async_new, &wq);
361
362 while (!kthread_should_stop()) {
363 int tc, ec;
364
365 set_current_state(TASK_INTERRUPTIBLE);
366
367 tc = atomic_read(&thread_count);
368 rmb();
369 ec = atomic_read(&entry_count);
370
371 while (tc < ec && tc < MAX_THREADS) {
Cornelia Huck86532d82009-01-19 13:45:31 +0100372 if (IS_ERR(kthread_run(async_thread, NULL, "async/%i",
373 tc))) {
374 msleep(100);
375 continue;
376 }
Arjan van de Ven22a9d642009-01-07 08:45:46 -0800377 atomic_inc(&thread_count);
378 tc++;
379 }
380
381 schedule();
382 }
383 remove_wait_queue(&async_new, &wq);
384
385 return 0;
386}
387
388static int __init async_init(void)
389{
Arjan van de Ven97107942009-03-15 11:11:44 -0700390 async_enabled =
391 !IS_ERR(kthread_run(async_manager_thread, NULL, "async/mgr"));
392
393 WARN_ON(!async_enabled);
Arjan van de Ven22a9d642009-01-07 08:45:46 -0800394 return 0;
395}
396
Arjan van de Ven22a9d642009-01-07 08:45:46 -0800397core_initcall(async_init);