Root/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
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>
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#include "workqueue_internal.h"
61
62static async_cookie_t next_cookie = 1;
63
64#define MAX_WORK 32768
65#define ASYNC_COOKIE_MAX ULLONG_MAX /* infinity cookie */
66
67static LIST_HEAD(async_global_pending); /* pending from all registered doms */
68static ASYNC_DOMAIN(async_dfl_domain);
69static DEFINE_SPINLOCK(async_lock);
70
71struct async_entry {
72    struct list_head domain_list;
73    struct list_head global_list;
74    struct work_struct work;
75    async_cookie_t cookie;
76    async_func_t func;
77    void *data;
78    struct async_domain *domain;
79};
80
81static DECLARE_WAIT_QUEUE_HEAD(async_done);
82
83static atomic_t entry_count;
84
85static async_cookie_t lowest_in_progress(struct async_domain *domain)
86{
87    struct list_head *pending;
88    async_cookie_t ret = ASYNC_COOKIE_MAX;
89    unsigned long flags;
90
91    spin_lock_irqsave(&async_lock, flags);
92
93    if (domain)
94        pending = &domain->pending;
95    else
96        pending = &async_global_pending;
97
98    if (!list_empty(pending))
99        ret = list_first_entry(pending, struct async_entry,
100                       domain_list)->cookie;
101
102    spin_unlock_irqrestore(&async_lock, flags);
103    return ret;
104}
105
106/*
107 * pick the first pending entry and run it
108 */
109static void async_run_entry_fn(struct work_struct *work)
110{
111    struct async_entry *entry =
112        container_of(work, struct async_entry, work);
113    unsigned long flags;
114    ktime_t uninitialized_var(calltime), delta, rettime;
115
116    /* 1) run (and print duration) */
117    if (initcall_debug && system_state == SYSTEM_BOOTING) {
118        printk(KERN_DEBUG "calling %lli_%pF @ %i\n",
119            (long long)entry->cookie,
120            entry->func, task_pid_nr(current));
121        calltime = ktime_get();
122    }
123    entry->func(entry->data, entry->cookie);
124    if (initcall_debug && system_state == SYSTEM_BOOTING) {
125        rettime = ktime_get();
126        delta = ktime_sub(rettime, calltime);
127        printk(KERN_DEBUG "initcall %lli_%pF returned 0 after %lld usecs\n",
128            (long long)entry->cookie,
129            entry->func,
130            (long long)ktime_to_ns(delta) >> 10);
131    }
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
148static async_cookie_t __async_schedule(async_func_t func, void *data, struct async_domain *domain)
149{
150    struct async_entry *entry;
151    unsigned long flags;
152    async_cookie_t newcookie;
153
154    /* allow irq-off callers */
155    entry = kzalloc(sizeof(struct async_entry), GFP_ATOMIC);
156
157    /*
158     * If we're out of memory or if there's too much work
159     * pending already, we execute synchronously.
160     */
161    if (!entry || atomic_read(&entry_count) > MAX_WORK) {
162        kfree(entry);
163        spin_lock_irqsave(&async_lock, flags);
164        newcookie = next_cookie++;
165        spin_unlock_irqrestore(&async_lock, flags);
166
167        /* low on memory.. run synchronously */
168        func(data, newcookie);
169        return newcookie;
170    }
171    INIT_LIST_HEAD(&entry->domain_list);
172    INIT_LIST_HEAD(&entry->global_list);
173    INIT_WORK(&entry->work, async_run_entry_fn);
174    entry->func = func;
175    entry->data = data;
176    entry->domain = domain;
177
178    spin_lock_irqsave(&async_lock, flags);
179
180    /* allocate cookie and queue */
181    newcookie = entry->cookie = next_cookie++;
182
183    list_add_tail(&entry->domain_list, &domain->pending);
184    if (domain->registered)
185        list_add_tail(&entry->global_list, &async_global_pending);
186
187    atomic_inc(&entry_count);
188    spin_unlock_irqrestore(&async_lock, flags);
189
190    /* mark that this task has queued an async job, used by module init */
191    current->flags |= PF_USED_ASYNC;
192
193    /* schedule for execution */
194    queue_work(system_unbound_wq, &entry->work);
195
196    return newcookie;
197}
198
199/**
200 * async_schedule - schedule a function for asynchronous execution
201 * @func: function to execute asynchronously
202 * @data: data pointer to pass to the function
203 *
204 * Returns an async_cookie_t that may be used for checkpointing later.
205 * Note: This function may be called from atomic or non-atomic contexts.
206 */
207async_cookie_t async_schedule(async_func_t func, void *data)
208{
209    return __async_schedule(func, data, &async_dfl_domain);
210}
211EXPORT_SYMBOL_GPL(async_schedule);
212
213/**
214 * async_schedule_domain - schedule a function for asynchronous execution within a certain domain
215 * @func: function to execute asynchronously
216 * @data: data pointer to pass to the function
217 * @domain: the domain
218 *
219 * Returns an async_cookie_t that may be used for checkpointing later.
220 * @domain may be used in the async_synchronize_*_domain() functions to
221 * wait within a certain synchronization domain rather than globally. A
222 * synchronization domain is specified via @domain. Note: This function
223 * may be called from atomic or non-atomic contexts.
224 */
225async_cookie_t async_schedule_domain(async_func_t func, void *data,
226                     struct async_domain *domain)
227{
228    return __async_schedule(func, data, domain);
229}
230EXPORT_SYMBOL_GPL(async_schedule_domain);
231
232/**
233 * async_synchronize_full - synchronize all asynchronous function calls
234 *
235 * This function waits until all asynchronous function calls have been done.
236 */
237void async_synchronize_full(void)
238{
239    async_synchronize_full_domain(NULL);
240}
241EXPORT_SYMBOL_GPL(async_synchronize_full);
242
243/**
244 * async_unregister_domain - ensure no more anonymous waiters on this domain
245 * @domain: idle domain to flush out of any async_synchronize_full instances
246 *
247 * async_synchronize_{cookie|full}_domain() are not flushed since callers
248 * of these routines should know the lifetime of @domain
249 *
250 * Prefer ASYNC_DOMAIN_EXCLUSIVE() declarations over flushing
251 */
252void async_unregister_domain(struct async_domain *domain)
253{
254    spin_lock_irq(&async_lock);
255    WARN_ON(!domain->registered || !list_empty(&domain->pending));
256    domain->registered = 0;
257    spin_unlock_irq(&async_lock);
258}
259EXPORT_SYMBOL_GPL(async_unregister_domain);
260
261/**
262 * async_synchronize_full_domain - synchronize all asynchronous function within a certain domain
263 * @domain: the domain to synchronize
264 *
265 * This function waits until all asynchronous function calls for the
266 * synchronization domain specified by @domain have been done.
267 */
268void async_synchronize_full_domain(struct async_domain *domain)
269{
270    async_synchronize_cookie_domain(ASYNC_COOKIE_MAX, domain);
271}
272EXPORT_SYMBOL_GPL(async_synchronize_full_domain);
273
274/**
275 * async_synchronize_cookie_domain - synchronize asynchronous function calls within a certain domain with cookie checkpointing
276 * @cookie: async_cookie_t to use as checkpoint
277 * @domain: the domain to synchronize (%NULL for all registered domains)
278 *
279 * This function waits until all asynchronous function calls for the
280 * synchronization domain specified by @domain submitted prior to @cookie
281 * have been done.
282 */
283void async_synchronize_cookie_domain(async_cookie_t cookie, struct async_domain *domain)
284{
285    ktime_t uninitialized_var(starttime), delta, endtime;
286
287    if (initcall_debug && system_state == SYSTEM_BOOTING) {
288        printk(KERN_DEBUG "async_waiting @ %i\n", task_pid_nr(current));
289        starttime = ktime_get();
290    }
291
292    wait_event(async_done, lowest_in_progress(domain) >= cookie);
293
294    if (initcall_debug && system_state == SYSTEM_BOOTING) {
295        endtime = ktime_get();
296        delta = ktime_sub(endtime, starttime);
297
298        printk(KERN_DEBUG "async_continuing @ %i after %lli usec\n",
299            task_pid_nr(current),
300            (long long)ktime_to_ns(delta) >> 10);
301    }
302}
303EXPORT_SYMBOL_GPL(async_synchronize_cookie_domain);
304
305/**
306 * async_synchronize_cookie - synchronize asynchronous function calls with cookie checkpointing
307 * @cookie: async_cookie_t to use as checkpoint
308 *
309 * This function waits until all asynchronous function calls prior to @cookie
310 * have been done.
311 */
312void async_synchronize_cookie(async_cookie_t cookie)
313{
314    async_synchronize_cookie_domain(cookie, &async_dfl_domain);
315}
316EXPORT_SYMBOL_GPL(async_synchronize_cookie);
317
318/**
319 * current_is_async - is %current an async worker task?
320 *
321 * Returns %true if %current is an async worker task.
322 */
323bool current_is_async(void)
324{
325    struct worker *worker = current_wq_worker();
326
327    return worker && worker->current_func == async_run_entry_fn;
328}
329

Archive Download this file



interactive