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 LIST_HEAD(async_global_pending); /* pending from all registered doms */
68 static ASYNC_DOMAIN(async_dfl_domain);
69 static DEFINE_SPINLOCK(async_lock);
72 struct list_head domain_list;
73 struct list_head global_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 struct async_entry *first = NULL;
88 async_cookie_t ret = ASYNC_COOKIE_MAX;
91 spin_lock_irqsave(&async_lock, flags);
94 if (!list_empty(&domain->pending))
95 first = list_first_entry(&domain->pending,
96 struct async_entry, domain_list);
98 if (!list_empty(&async_global_pending))
99 first = list_first_entry(&async_global_pending,
100 struct async_entry, global_list);
106 spin_unlock_irqrestore(&async_lock, flags);
111 * pick the first pending entry and run it
113 static void async_run_entry_fn(struct work_struct *work)
115 struct async_entry *entry =
116 container_of(work, struct async_entry, work);
118 ktime_t uninitialized_var(calltime), delta, rettime;
120 /* 1) run (and print duration) */
121 if (initcall_debug && system_state < SYSTEM_RUNNING) {
122 pr_debug("calling %lli_%pF @ %i\n",
123 (long long)entry->cookie,
124 entry->func, task_pid_nr(current));
125 calltime = ktime_get();
127 entry->func(entry->data, entry->cookie);
128 if (initcall_debug && system_state < SYSTEM_RUNNING) {
129 rettime = ktime_get();
130 delta = ktime_sub(rettime, calltime);
131 pr_debug("initcall %lli_%pF returned 0 after %lld usecs\n",
132 (long long)entry->cookie,
134 (long long)ktime_to_ns(delta) >> 10);
137 /* 2) remove self from the pending queues */
138 spin_lock_irqsave(&async_lock, flags);
139 list_del_init(&entry->domain_list);
140 list_del_init(&entry->global_list);
142 /* 3) free the entry */
144 atomic_dec(&entry_count);
146 spin_unlock_irqrestore(&async_lock, flags);
148 /* 4) wake up any waiters */
149 wake_up(&async_done);
152 static async_cookie_t __async_schedule(async_func_t func, void *data, struct async_domain *domain)
154 struct async_entry *entry;
156 async_cookie_t newcookie;
158 /* allow irq-off callers */
159 entry = kzalloc(sizeof(struct async_entry), GFP_ATOMIC);
162 * If we're out of memory or if there's too much work
163 * pending already, we execute synchronously.
165 if (!entry || atomic_read(&entry_count) > MAX_WORK) {
167 spin_lock_irqsave(&async_lock, flags);
168 newcookie = next_cookie++;
169 spin_unlock_irqrestore(&async_lock, flags);
171 /* low on memory.. run synchronously */
172 func(data, newcookie);
175 INIT_LIST_HEAD(&entry->domain_list);
176 INIT_LIST_HEAD(&entry->global_list);
177 INIT_WORK(&entry->work, async_run_entry_fn);
180 entry->domain = domain;
182 spin_lock_irqsave(&async_lock, flags);
184 /* allocate cookie and queue */
185 newcookie = entry->cookie = next_cookie++;
187 list_add_tail(&entry->domain_list, &domain->pending);
188 if (domain->registered)
189 list_add_tail(&entry->global_list, &async_global_pending);
191 atomic_inc(&entry_count);
192 spin_unlock_irqrestore(&async_lock, flags);
194 /* schedule for execution */
195 queue_work(system_unbound_wq, &entry->work);
201 * async_schedule - schedule a function for asynchronous execution
202 * @func: function to execute asynchronously
203 * @data: data pointer to pass to the function
205 * Returns an async_cookie_t that may be used for checkpointing later.
206 * Note: This function may be called from atomic or non-atomic contexts.
208 async_cookie_t async_schedule(async_func_t func, void *data)
210 return __async_schedule(func, data, &async_dfl_domain);
212 EXPORT_SYMBOL_GPL(async_schedule);
215 * async_schedule_domain - schedule a function for asynchronous execution within a certain domain
216 * @func: function to execute asynchronously
217 * @data: data pointer to pass to the function
218 * @domain: the domain
220 * Returns an async_cookie_t that may be used for checkpointing later.
221 * @domain may be used in the async_synchronize_*_domain() functions to
222 * wait within a certain synchronization domain rather than globally. A
223 * synchronization domain is specified via @domain. Note: This function
224 * may be called from atomic or non-atomic contexts.
226 async_cookie_t async_schedule_domain(async_func_t func, void *data,
227 struct async_domain *domain)
229 return __async_schedule(func, data, domain);
231 EXPORT_SYMBOL_GPL(async_schedule_domain);
234 * async_synchronize_full - synchronize all asynchronous function calls
236 * This function waits until all asynchronous function calls have been done.
238 void async_synchronize_full(void)
240 async_synchronize_full_domain(NULL);
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 spin_lock_irq(&async_lock);
256 WARN_ON(!domain->registered || !list_empty(&domain->pending));
257 domain->registered = 0;
258 spin_unlock_irq(&async_lock);
260 EXPORT_SYMBOL_GPL(async_unregister_domain);
263 * async_synchronize_full_domain - synchronize all asynchronous function within a certain domain
264 * @domain: the domain to synchronize
266 * This function waits until all asynchronous function calls for the
267 * synchronization domain specified by @domain have been done.
269 void async_synchronize_full_domain(struct async_domain *domain)
271 async_synchronize_cookie_domain(ASYNC_COOKIE_MAX, domain);
273 EXPORT_SYMBOL_GPL(async_synchronize_full_domain);
276 * async_synchronize_cookie_domain - synchronize asynchronous function calls within a certain domain with cookie checkpointing
277 * @cookie: async_cookie_t to use as checkpoint
278 * @domain: the domain to synchronize (%NULL for all registered domains)
280 * This function waits until all asynchronous function calls for the
281 * synchronization domain specified by @domain submitted prior to @cookie
284 void async_synchronize_cookie_domain(async_cookie_t cookie, struct async_domain *domain)
286 ktime_t uninitialized_var(starttime), delta, endtime;
288 if (initcall_debug && system_state < SYSTEM_RUNNING) {
289 pr_debug("async_waiting @ %i\n", task_pid_nr(current));
290 starttime = ktime_get();
293 wait_event(async_done, lowest_in_progress(domain) >= cookie);
295 if (initcall_debug && system_state < SYSTEM_RUNNING) {
296 endtime = ktime_get();
297 delta = ktime_sub(endtime, starttime);
299 pr_debug("async_continuing @ %i after %lli usec\n",
300 task_pid_nr(current),
301 (long long)ktime_to_ns(delta) >> 10);
304 EXPORT_SYMBOL_GPL(async_synchronize_cookie_domain);
307 * async_synchronize_cookie - synchronize asynchronous function calls with cookie checkpointing
308 * @cookie: async_cookie_t to use as checkpoint
310 * This function waits until all asynchronous function calls prior to @cookie
313 void async_synchronize_cookie(async_cookie_t cookie)
315 async_synchronize_cookie_domain(cookie, &async_dfl_domain);
317 EXPORT_SYMBOL_GPL(async_synchronize_cookie);
320 * current_is_async - is %current an async worker task?
322 * Returns %true if %current is an async worker task.
324 bool current_is_async(void)
326 struct worker *worker = current_wq_worker();
328 return worker && worker->current_func == async_run_entry_fn;
330 EXPORT_SYMBOL_GPL(current_is_async);