1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * async.c: Asynchronous function calls for boot performance
4 *
5 * (C) Copyright 2009 Intel Corporation
6 * Author: Arjan van de Ven <arjan@linux.intel.com>
7 */
8
9
10 /*
11
12 Goals and Theory of Operation
13
14 The primary goal of this feature is to reduce the kernel boot time,
15 by doing various independent hardware delays and discovery operations
16 decoupled and not strictly serialized.
17
18 More specifically, the asynchronous function call concept allows
19 certain operations (primarily during system boot) to happen
20 asynchronously, out of order, while these operations still
21 have their externally visible parts happen sequentially and in-order.
22 (not unlike how out-of-order CPUs retire their instructions in order)
23
24 Key to the asynchronous function call implementation is the concept of
25 a "sequence cookie" (which, although it has an abstracted type, can be
26 thought of as a monotonically incrementing number).
27
28 The async core will assign each scheduled event such a sequence cookie and
29 pass this to the called functions.
30
31 The asynchronously called function should before doing a globally visible
32 operation, such as registering device numbers, call the
33 async_synchronize_cookie() function and pass in its own cookie. The
34 async_synchronize_cookie() function will make sure that all asynchronous
35 operations that were scheduled prior to the operation corresponding with the
36 cookie have completed.
37
38 Subsystem/driver initialization code that scheduled asynchronous probe
39 functions, but which shares global resources with other drivers/subsystems
40 that do not use the asynchronous call feature, need to do a full
41 synchronization with the async_synchronize_full() function, before returning
42 from their init function. This is to maintain strict ordering between the
43 asynchronous and synchronous parts of the kernel.
44
45 */
46
47 #include <linux/async.h>
48 #include <linux/atomic.h>
49 #include <linux/ktime.h>
50 #include <linux/export.h>
51 #include <linux/wait.h>
52 #include <linux/sched.h>
53 #include <linux/slab.h>
54 #include <linux/workqueue.h>
55
56 #include "workqueue_internal.h"
57
58 static async_cookie_t next_cookie = 1;
59
60 #define MAX_WORK 32768
61 #define ASYNC_COOKIE_MAX ULLONG_MAX /* infinity cookie */
62
63 static LIST_HEAD(async_global_pending); /* pending from all registered doms */
64 static ASYNC_DOMAIN(async_dfl_domain);
65 static DEFINE_SPINLOCK(async_lock);
66
67 struct async_entry {
68 struct list_head domain_list;
69 struct list_head global_list;
70 struct work_struct work;
71 async_cookie_t cookie;
72 async_func_t func;
73 void *data;
74 struct async_domain *domain;
75 };
76
77 static DECLARE_WAIT_QUEUE_HEAD(async_done);
78
79 static atomic_t entry_count;
80
microseconds_since(ktime_t start)81 static long long microseconds_since(ktime_t start)
82 {
83 ktime_t now = ktime_get();
84 return ktime_to_ns(ktime_sub(now, start)) >> 10;
85 }
86
lowest_in_progress(struct async_domain * domain)87 static async_cookie_t lowest_in_progress(struct async_domain *domain)
88 {
89 struct async_entry *first = NULL;
90 async_cookie_t ret = ASYNC_COOKIE_MAX;
91 unsigned long flags;
92
93 spin_lock_irqsave(&async_lock, flags);
94
95 if (domain) {
96 if (!list_empty(&domain->pending))
97 first = list_first_entry(&domain->pending,
98 struct async_entry, domain_list);
99 } else {
100 if (!list_empty(&async_global_pending))
101 first = list_first_entry(&async_global_pending,
102 struct async_entry, global_list);
103 }
104
105 if (first)
106 ret = first->cookie;
107
108 spin_unlock_irqrestore(&async_lock, flags);
109 return ret;
110 }
111
112 /*
113 * pick the first pending entry and run it
114 */
async_run_entry_fn(struct work_struct * work)115 static void async_run_entry_fn(struct work_struct *work)
116 {
117 struct async_entry *entry =
118 container_of(work, struct async_entry, work);
119 unsigned long flags;
120 ktime_t calltime;
121
122 /* 1) run (and print duration) */
123 pr_debug("calling %lli_%pS @ %i\n", (long long)entry->cookie,
124 entry->func, task_pid_nr(current));
125 calltime = ktime_get();
126
127 entry->func(entry->data, entry->cookie);
128
129 pr_debug("initcall %lli_%pS returned after %lld usecs\n",
130 (long long)entry->cookie, entry->func,
131 microseconds_since(calltime));
132
133 /* 2) remove self from the pending queues */
134 spin_lock_irqsave(&async_lock, flags);
135 list_del_init(&entry->domain_list);
136 list_del_init(&entry->global_list);
137
138 /* 3) free the entry */
139 kfree(entry);
140 atomic_dec(&entry_count);
141
142 spin_unlock_irqrestore(&async_lock, flags);
143
144 /* 4) wake up any waiters */
145 wake_up(&async_done);
146 }
147
148 /**
149 * async_schedule_node_domain - NUMA specific version of async_schedule_domain
150 * @func: function to execute asynchronously
151 * @data: data pointer to pass to the function
152 * @node: NUMA node that we want to schedule this on or close to
153 * @domain: the domain
154 *
155 * Returns an async_cookie_t that may be used for checkpointing later.
156 * @domain may be used in the async_synchronize_*_domain() functions to
157 * wait within a certain synchronization domain rather than globally.
158 *
159 * Note: This function may be called from atomic or non-atomic contexts.
160 *
161 * The node requested will be honored on a best effort basis. If the node
162 * has no CPUs associated with it then the work is distributed among all
163 * available CPUs.
164 */
async_schedule_node_domain(async_func_t func,void * data,int node,struct async_domain * domain)165 async_cookie_t async_schedule_node_domain(async_func_t func, void *data,
166 int node, struct async_domain *domain)
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 func(data, newcookie);
187 return newcookie;
188 }
189 INIT_LIST_HEAD(&entry->domain_list);
190 INIT_LIST_HEAD(&entry->global_list);
191 INIT_WORK(&entry->work, async_run_entry_fn);
192 entry->func = func;
193 entry->data = data;
194 entry->domain = domain;
195
196 spin_lock_irqsave(&async_lock, flags);
197
198 /* allocate cookie and queue */
199 newcookie = entry->cookie = next_cookie++;
200
201 list_add_tail(&entry->domain_list, &domain->pending);
202 if (domain->registered)
203 list_add_tail(&entry->global_list, &async_global_pending);
204
205 atomic_inc(&entry_count);
206 spin_unlock_irqrestore(&async_lock, flags);
207
208 /* schedule for execution */
209 queue_work_node(node, system_unbound_wq, &entry->work);
210
211 return newcookie;
212 }
213 EXPORT_SYMBOL_GPL(async_schedule_node_domain);
214
215 /**
216 * async_schedule_node - NUMA specific version of async_schedule
217 * @func: function to execute asynchronously
218 * @data: data pointer to pass to the function
219 * @node: NUMA node that we want to schedule this on or close to
220 *
221 * Returns an async_cookie_t that may be used for checkpointing later.
222 * Note: This function may be called from atomic or non-atomic contexts.
223 *
224 * The node requested will be honored on a best effort basis. If the node
225 * has no CPUs associated with it then the work is distributed among all
226 * available CPUs.
227 */
async_schedule_node(async_func_t func,void * data,int node)228 async_cookie_t async_schedule_node(async_func_t func, void *data, int node)
229 {
230 return async_schedule_node_domain(func, data, node, &async_dfl_domain);
231 }
232 EXPORT_SYMBOL_GPL(async_schedule_node);
233
234 /**
235 * async_synchronize_full - synchronize all asynchronous function calls
236 *
237 * This function waits until all asynchronous function calls have been done.
238 */
async_synchronize_full(void)239 void async_synchronize_full(void)
240 {
241 async_synchronize_full_domain(NULL);
242 }
243 EXPORT_SYMBOL_GPL(async_synchronize_full);
244
245 /**
246 * async_synchronize_full_domain - synchronize all asynchronous function within a certain domain
247 * @domain: the domain to synchronize
248 *
249 * This function waits until all asynchronous function calls for the
250 * synchronization domain specified by @domain have been done.
251 */
async_synchronize_full_domain(struct async_domain * domain)252 void async_synchronize_full_domain(struct async_domain *domain)
253 {
254 async_synchronize_cookie_domain(ASYNC_COOKIE_MAX, domain);
255 }
256 EXPORT_SYMBOL_GPL(async_synchronize_full_domain);
257
258 /**
259 * async_synchronize_cookie_domain - synchronize asynchronous function calls within a certain domain with cookie checkpointing
260 * @cookie: async_cookie_t to use as checkpoint
261 * @domain: the domain to synchronize (%NULL for all registered domains)
262 *
263 * This function waits until all asynchronous function calls for the
264 * synchronization domain specified by @domain submitted prior to @cookie
265 * have been done.
266 */
async_synchronize_cookie_domain(async_cookie_t cookie,struct async_domain * domain)267 void async_synchronize_cookie_domain(async_cookie_t cookie, struct async_domain *domain)
268 {
269 ktime_t starttime;
270
271 pr_debug("async_waiting @ %i\n", task_pid_nr(current));
272 starttime = ktime_get();
273
274 wait_event(async_done, lowest_in_progress(domain) >= cookie);
275
276 pr_debug("async_continuing @ %i after %lli usec\n", task_pid_nr(current),
277 microseconds_since(starttime));
278 }
279 EXPORT_SYMBOL_GPL(async_synchronize_cookie_domain);
280
281 /**
282 * async_synchronize_cookie - synchronize asynchronous function calls with cookie checkpointing
283 * @cookie: async_cookie_t to use as checkpoint
284 *
285 * This function waits until all asynchronous function calls prior to @cookie
286 * have been done.
287 */
async_synchronize_cookie(async_cookie_t cookie)288 void async_synchronize_cookie(async_cookie_t cookie)
289 {
290 async_synchronize_cookie_domain(cookie, &async_dfl_domain);
291 }
292 EXPORT_SYMBOL_GPL(async_synchronize_cookie);
293
294 /**
295 * current_is_async - is %current an async worker task?
296 *
297 * Returns %true if %current is an async worker task.
298 */
current_is_async(void)299 bool current_is_async(void)
300 {
301 struct worker *worker = current_wq_worker();
302
303 return worker && worker->current_func == async_run_entry_fn;
304 }
305 EXPORT_SYMBOL_GPL(current_is_async);
306
