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
60static async_cookie_t next_cookie = 1;
61
62#define MAX_WORK 32768
63
64static LIST_HEAD(async_pending);
65static LIST_HEAD(async_running);
66static DEFINE_SPINLOCK(async_lock);
67
68struct async_entry {
69    struct list_head list;
70    struct work_struct work;
71    async_cookie_t cookie;
72    async_func_ptr *func;
73    void *data;
74    struct list_head *running;
75};
76
77static DECLARE_WAIT_QUEUE_HEAD(async_done);
78
79static atomic_t entry_count;
80
81
82/*
83 * MUST be called with the lock held!
84 */
85static async_cookie_t __lowest_in_progress(struct list_head *running)
86{
87    struct async_entry *entry;
88
89    if (!list_empty(running)) {
90        entry = list_first_entry(running,
91            struct async_entry, list);
92        return entry->cookie;
93    }
94
95    list_for_each_entry(entry, &async_pending, list)
96        if (entry->running == running)
97            return entry->cookie;
98
99    return next_cookie; /* "infinity" value */
100}
101
102static async_cookie_t lowest_in_progress(struct list_head *running)
103{
104    unsigned long flags;
105    async_cookie_t ret;
106
107    spin_lock_irqsave(&async_lock, flags);
108    ret = __lowest_in_progress(running);
109    spin_unlock_irqrestore(&async_lock, flags);
110    return ret;
111}
112
113/*
114 * pick the first pending entry and run it
115 */
116static void async_run_entry_fn(struct work_struct *work)
117{
118    struct async_entry *entry =
119        container_of(work, struct async_entry, work);
120    unsigned long flags;
121    ktime_t uninitialized_var(calltime), delta, rettime;
122
123    /* 1) move self to the running queue */
124    spin_lock_irqsave(&async_lock, flags);
125    list_move_tail(&entry->list, entry->running);
126    spin_unlock_irqrestore(&async_lock, flags);
127
128    /* 2) run (and print duration) */
129    if (initcall_debug && system_state == SYSTEM_BOOTING) {
130        printk(KERN_DEBUG "calling %lli_%pF @ %i\n",
131            (long long)entry->cookie,
132            entry->func, task_pid_nr(current));
133        calltime = ktime_get();
134    }
135    entry->func(entry->data, entry->cookie);
136    if (initcall_debug && system_state == SYSTEM_BOOTING) {
137        rettime = ktime_get();
138        delta = ktime_sub(rettime, calltime);
139        printk(KERN_DEBUG "initcall %lli_%pF returned 0 after %lld usecs\n",
140            (long long)entry->cookie,
141            entry->func,
142            (long long)ktime_to_ns(delta) >> 10);
143    }
144
145    /* 3) remove self from the running queue */
146    spin_lock_irqsave(&async_lock, flags);
147    list_del(&entry->list);
148
149    /* 4) free the entry */
150    kfree(entry);
151    atomic_dec(&entry_count);
152
153    spin_unlock_irqrestore(&async_lock, flags);
154
155    /* 5) wake up any waiters */
156    wake_up(&async_done);
157}
158
159static async_cookie_t __async_schedule(async_func_ptr *ptr, void *data, struct list_head *running)
160{
161    struct async_entry *entry;
162    unsigned long flags;
163    async_cookie_t newcookie;
164
165    /* allow irq-off callers */
166    entry = kzalloc(sizeof(struct async_entry), GFP_ATOMIC);
167
168    /*
169     * If we're out of memory or if there's too much work
170     * pending already, we execute synchronously.
171     */
172    if (!entry || atomic_read(&entry_count) > MAX_WORK) {
173        kfree(entry);
174        spin_lock_irqsave(&async_lock, flags);
175        newcookie = next_cookie++;
176        spin_unlock_irqrestore(&async_lock, flags);
177
178        /* low on memory.. run synchronously */
179        ptr(data, newcookie);
180        return newcookie;
181    }
182    INIT_WORK(&entry->work, async_run_entry_fn);
183    entry->func = ptr;
184    entry->data = data;
185    entry->running = running;
186
187    spin_lock_irqsave(&async_lock, flags);
188    newcookie = entry->cookie = next_cookie++;
189    list_add_tail(&entry->list, &async_pending);
190    atomic_inc(&entry_count);
191    spin_unlock_irqrestore(&async_lock, flags);
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 * @ptr: 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_ptr *ptr, void *data)
208{
209    return __async_schedule(ptr, data, &async_running);
210}
211EXPORT_SYMBOL_GPL(async_schedule);
212
213/**
214 * async_schedule_domain - schedule a function for asynchronous execution within a certain domain
215 * @ptr: function to execute asynchronously
216 * @data: data pointer to pass to the function
217 * @running: running list for the domain
218 *
219 * Returns an async_cookie_t that may be used for checkpointing later.
220 * @running may be used in the async_synchronize_*_domain() functions
221 * to wait within a certain synchronization domain rather than globally.
222 * A synchronization domain is specified via the running queue @running to use.
223 * Note: This function may be called from atomic or non-atomic contexts.
224 */
225async_cookie_t async_schedule_domain(async_func_ptr *ptr, void *data,
226                     struct list_head *running)
227{
228    return __async_schedule(ptr, data, running);
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    do {
240        async_synchronize_cookie(next_cookie);
241    } while (!list_empty(&async_running) || !list_empty(&async_pending));
242}
243EXPORT_SYMBOL_GPL(async_synchronize_full);
244
245/**
246 * async_synchronize_full_domain - synchronize all asynchronous function within a certain domain
247 * @list: running list to synchronize on
248 *
249 * This function waits until all asynchronous function calls for the
250 * synchronization domain specified by the running list @list have been done.
251 */
252void async_synchronize_full_domain(struct list_head *list)
253{
254    async_synchronize_cookie_domain(next_cookie, list);
255}
256EXPORT_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 * @running: running list to synchronize on
262 *
263 * This function waits until all asynchronous function calls for the
264 * synchronization domain specified by the running list @list submitted
265 * prior to @cookie have been done.
266 */
267void async_synchronize_cookie_domain(async_cookie_t cookie,
268                     struct list_head *running)
269{
270    ktime_t uninitialized_var(starttime), delta, endtime;
271
272    if (initcall_debug && system_state == SYSTEM_BOOTING) {
273        printk(KERN_DEBUG "async_waiting @ %i\n", task_pid_nr(current));
274        starttime = ktime_get();
275    }
276
277    wait_event(async_done, lowest_in_progress(running) >= cookie);
278
279    if (initcall_debug && system_state == SYSTEM_BOOTING) {
280        endtime = ktime_get();
281        delta = ktime_sub(endtime, starttime);
282
283        printk(KERN_DEBUG "async_continuing @ %i after %lli usec\n",
284            task_pid_nr(current),
285            (long long)ktime_to_ns(delta) >> 10);
286    }
287}
288EXPORT_SYMBOL_GPL(async_synchronize_cookie_domain);
289
290/**
291 * async_synchronize_cookie - synchronize asynchronous function calls with cookie checkpointing
292 * @cookie: async_cookie_t to use as checkpoint
293 *
294 * This function waits until all asynchronous function calls prior to @cookie
295 * have been done.
296 */
297void async_synchronize_cookie(async_cookie_t cookie)
298{
299    async_synchronize_cookie_domain(cookie, &async_running);
300}
301EXPORT_SYMBOL_GPL(async_synchronize_cookie);
302

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