Arjan van de Ven | 22a9d64 | 2009-01-07 08:45:46 -0800 | [diff] [blame] | 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 | |
| 16 | Goals and Theory of Operation |
| 17 | |
| 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. |
| 21 | |
| 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) |
| 27 | |
| 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). |
| 31 | |
| 32 | The async core will assign each scheduled event such a sequence cookie and |
| 33 | pass this to the called functions. |
| 34 | |
| 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. |
| 41 | |
| 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. |
| 48 | |
| 49 | */ |
| 50 | |
| 51 | #include <linux/async.h> |
| 52 | #include <linux/module.h> |
| 53 | #include <linux/wait.h> |
| 54 | #include <linux/sched.h> |
| 55 | #include <linux/init.h> |
| 56 | #include <linux/kthread.h> |
| 57 | #include <asm/atomic.h> |
| 58 | |
| 59 | static async_cookie_t next_cookie = 1; |
| 60 | |
| 61 | #define MAX_THREADS 256 |
| 62 | #define MAX_WORK 32768 |
| 63 | |
| 64 | static LIST_HEAD(async_pending); |
| 65 | static LIST_HEAD(async_running); |
| 66 | static DEFINE_SPINLOCK(async_lock); |
| 67 | |
Arjan van de Ven | cdb80f6 | 2009-01-09 13:23:45 -0800 | [diff] [blame^] | 68 | static int async_enabled = 0; |
| 69 | |
Arjan van de Ven | 22a9d64 | 2009-01-07 08:45:46 -0800 | [diff] [blame] | 70 | struct async_entry { |
| 71 | struct list_head list; |
| 72 | async_cookie_t cookie; |
| 73 | async_func_ptr *func; |
| 74 | void *data; |
| 75 | struct list_head *running; |
| 76 | }; |
| 77 | |
| 78 | static DECLARE_WAIT_QUEUE_HEAD(async_done); |
| 79 | static DECLARE_WAIT_QUEUE_HEAD(async_new); |
| 80 | |
| 81 | static atomic_t entry_count; |
| 82 | static atomic_t thread_count; |
| 83 | |
| 84 | extern int initcall_debug; |
| 85 | |
| 86 | |
| 87 | /* |
| 88 | * MUST be called with the lock held! |
| 89 | */ |
| 90 | static async_cookie_t __lowest_in_progress(struct list_head *running) |
| 91 | { |
| 92 | struct async_entry *entry; |
| 93 | if (!list_empty(&async_pending)) { |
| 94 | entry = list_first_entry(&async_pending, |
| 95 | struct async_entry, list); |
| 96 | return entry->cookie; |
| 97 | } else if (!list_empty(running)) { |
| 98 | entry = list_first_entry(running, |
| 99 | struct async_entry, list); |
| 100 | return entry->cookie; |
| 101 | } else { |
| 102 | /* nothing in progress... next_cookie is "infinity" */ |
| 103 | return next_cookie; |
| 104 | } |
| 105 | |
| 106 | } |
| 107 | /* |
| 108 | * pick the first pending entry and run it |
| 109 | */ |
| 110 | static void run_one_entry(void) |
| 111 | { |
| 112 | unsigned long flags; |
| 113 | struct async_entry *entry; |
| 114 | ktime_t calltime, delta, rettime; |
| 115 | |
| 116 | /* 1) pick one task from the pending queue */ |
| 117 | |
| 118 | spin_lock_irqsave(&async_lock, flags); |
| 119 | if (list_empty(&async_pending)) |
| 120 | goto out; |
| 121 | entry = list_first_entry(&async_pending, struct async_entry, list); |
| 122 | |
| 123 | /* 2) move it to the running queue */ |
| 124 | list_del(&entry->list); |
| 125 | list_add_tail(&entry->list, &async_running); |
| 126 | spin_unlock_irqrestore(&async_lock, flags); |
| 127 | |
| 128 | /* 3) run it (and print duration)*/ |
Arjan van de Ven | ad160d2 | 2009-01-07 09:28:53 -0800 | [diff] [blame] | 129 | if (initcall_debug && system_state == SYSTEM_BOOTING) { |
Arjan van de Ven | 22a9d64 | 2009-01-07 08:45:46 -0800 | [diff] [blame] | 130 | printk("calling %lli_%pF @ %i\n", entry->cookie, entry->func, task_pid_nr(current)); |
| 131 | calltime = ktime_get(); |
| 132 | } |
| 133 | entry->func(entry->data, entry->cookie); |
Arjan van de Ven | ad160d2 | 2009-01-07 09:28:53 -0800 | [diff] [blame] | 134 | if (initcall_debug && system_state == SYSTEM_BOOTING) { |
Arjan van de Ven | 22a9d64 | 2009-01-07 08:45:46 -0800 | [diff] [blame] | 135 | rettime = ktime_get(); |
| 136 | delta = ktime_sub(rettime, calltime); |
| 137 | printk("initcall %lli_%pF returned 0 after %lld usecs\n", entry->cookie, |
| 138 | entry->func, ktime_to_ns(delta) >> 10); |
| 139 | } |
| 140 | |
| 141 | /* 4) remove it from the running queue */ |
| 142 | spin_lock_irqsave(&async_lock, flags); |
| 143 | list_del(&entry->list); |
| 144 | |
| 145 | /* 5) free the entry */ |
| 146 | kfree(entry); |
| 147 | atomic_dec(&entry_count); |
| 148 | |
| 149 | spin_unlock_irqrestore(&async_lock, flags); |
| 150 | |
| 151 | /* 6) wake up any waiters. */ |
| 152 | wake_up(&async_done); |
| 153 | return; |
| 154 | |
| 155 | out: |
| 156 | spin_unlock_irqrestore(&async_lock, flags); |
| 157 | } |
| 158 | |
| 159 | |
| 160 | static async_cookie_t __async_schedule(async_func_ptr *ptr, void *data, struct list_head *running) |
| 161 | { |
| 162 | struct async_entry *entry; |
| 163 | unsigned long flags; |
| 164 | async_cookie_t newcookie; |
| 165 | |
| 166 | |
| 167 | /* allow irq-off callers */ |
| 168 | entry = kzalloc(sizeof(struct async_entry), GFP_ATOMIC); |
| 169 | |
| 170 | /* |
| 171 | * If we're out of memory or if there's too much work |
| 172 | * pending already, we execute synchronously. |
| 173 | */ |
Arjan van de Ven | cdb80f6 | 2009-01-09 13:23:45 -0800 | [diff] [blame^] | 174 | if (!async_enabled || !entry || atomic_read(&entry_count) > MAX_WORK) { |
Arjan van de Ven | 22a9d64 | 2009-01-07 08:45:46 -0800 | [diff] [blame] | 175 | kfree(entry); |
| 176 | spin_lock_irqsave(&async_lock, flags); |
| 177 | newcookie = next_cookie++; |
| 178 | spin_unlock_irqrestore(&async_lock, flags); |
| 179 | |
| 180 | /* low on memory.. run synchronously */ |
| 181 | ptr(data, newcookie); |
| 182 | return newcookie; |
| 183 | } |
| 184 | entry->func = ptr; |
| 185 | entry->data = data; |
| 186 | entry->running = running; |
| 187 | |
| 188 | spin_lock_irqsave(&async_lock, flags); |
| 189 | newcookie = entry->cookie = next_cookie++; |
| 190 | list_add_tail(&entry->list, &async_pending); |
| 191 | atomic_inc(&entry_count); |
| 192 | spin_unlock_irqrestore(&async_lock, flags); |
| 193 | wake_up(&async_new); |
| 194 | return newcookie; |
| 195 | } |
| 196 | |
| 197 | async_cookie_t async_schedule(async_func_ptr *ptr, void *data) |
| 198 | { |
| 199 | return __async_schedule(ptr, data, &async_pending); |
| 200 | } |
| 201 | EXPORT_SYMBOL_GPL(async_schedule); |
| 202 | |
| 203 | async_cookie_t async_schedule_special(async_func_ptr *ptr, void *data, struct list_head *running) |
| 204 | { |
| 205 | return __async_schedule(ptr, data, running); |
| 206 | } |
| 207 | EXPORT_SYMBOL_GPL(async_schedule_special); |
| 208 | |
| 209 | void async_synchronize_full(void) |
| 210 | { |
Arjan van de Ven | 33b04b9 | 2009-01-08 12:35:11 -0800 | [diff] [blame] | 211 | do { |
| 212 | async_synchronize_cookie(next_cookie); |
| 213 | } while (!list_empty(&async_running) || !list_empty(&async_pending)); |
Arjan van de Ven | 22a9d64 | 2009-01-07 08:45:46 -0800 | [diff] [blame] | 214 | } |
| 215 | EXPORT_SYMBOL_GPL(async_synchronize_full); |
| 216 | |
| 217 | void async_synchronize_full_special(struct list_head *list) |
| 218 | { |
| 219 | async_synchronize_cookie_special(next_cookie, list); |
| 220 | } |
| 221 | EXPORT_SYMBOL_GPL(async_synchronize_full_special); |
| 222 | |
| 223 | void async_synchronize_cookie_special(async_cookie_t cookie, struct list_head *running) |
| 224 | { |
| 225 | ktime_t starttime, delta, endtime; |
| 226 | |
Arjan van de Ven | ad160d2 | 2009-01-07 09:28:53 -0800 | [diff] [blame] | 227 | if (initcall_debug && system_state == SYSTEM_BOOTING) { |
Arjan van de Ven | 22a9d64 | 2009-01-07 08:45:46 -0800 | [diff] [blame] | 228 | printk("async_waiting @ %i\n", task_pid_nr(current)); |
| 229 | starttime = ktime_get(); |
| 230 | } |
| 231 | |
| 232 | wait_event(async_done, __lowest_in_progress(running) >= cookie); |
| 233 | |
Arjan van de Ven | ad160d2 | 2009-01-07 09:28:53 -0800 | [diff] [blame] | 234 | if (initcall_debug && system_state == SYSTEM_BOOTING) { |
Arjan van de Ven | 22a9d64 | 2009-01-07 08:45:46 -0800 | [diff] [blame] | 235 | endtime = ktime_get(); |
| 236 | delta = ktime_sub(endtime, starttime); |
| 237 | |
| 238 | printk("async_continuing @ %i after %lli usec\n", |
| 239 | task_pid_nr(current), ktime_to_ns(delta) >> 10); |
| 240 | } |
| 241 | } |
| 242 | EXPORT_SYMBOL_GPL(async_synchronize_cookie_special); |
| 243 | |
| 244 | void async_synchronize_cookie(async_cookie_t cookie) |
| 245 | { |
| 246 | async_synchronize_cookie_special(cookie, &async_running); |
| 247 | } |
| 248 | EXPORT_SYMBOL_GPL(async_synchronize_cookie); |
| 249 | |
| 250 | |
| 251 | static int async_thread(void *unused) |
| 252 | { |
| 253 | DECLARE_WAITQUEUE(wq, current); |
| 254 | add_wait_queue(&async_new, &wq); |
| 255 | |
| 256 | while (!kthread_should_stop()) { |
| 257 | int ret = HZ; |
| 258 | set_current_state(TASK_INTERRUPTIBLE); |
| 259 | /* |
| 260 | * check the list head without lock.. false positives |
| 261 | * are dealt with inside run_one_entry() while holding |
| 262 | * the lock. |
| 263 | */ |
| 264 | rmb(); |
| 265 | if (!list_empty(&async_pending)) |
| 266 | run_one_entry(); |
| 267 | else |
| 268 | ret = schedule_timeout(HZ); |
| 269 | |
| 270 | if (ret == 0) { |
| 271 | /* |
| 272 | * we timed out, this means we as thread are redundant. |
| 273 | * we sign off and die, but we to avoid any races there |
| 274 | * is a last-straw check to see if work snuck in. |
| 275 | */ |
| 276 | atomic_dec(&thread_count); |
| 277 | wmb(); /* manager must see our departure first */ |
| 278 | if (list_empty(&async_pending)) |
| 279 | break; |
| 280 | /* |
| 281 | * woops work came in between us timing out and us |
| 282 | * signing off; we need to stay alive and keep working. |
| 283 | */ |
| 284 | atomic_inc(&thread_count); |
| 285 | } |
| 286 | } |
| 287 | remove_wait_queue(&async_new, &wq); |
| 288 | |
| 289 | return 0; |
| 290 | } |
| 291 | |
| 292 | static int async_manager_thread(void *unused) |
| 293 | { |
| 294 | DECLARE_WAITQUEUE(wq, current); |
| 295 | add_wait_queue(&async_new, &wq); |
| 296 | |
| 297 | while (!kthread_should_stop()) { |
| 298 | int tc, ec; |
| 299 | |
| 300 | set_current_state(TASK_INTERRUPTIBLE); |
| 301 | |
| 302 | tc = atomic_read(&thread_count); |
| 303 | rmb(); |
| 304 | ec = atomic_read(&entry_count); |
| 305 | |
| 306 | while (tc < ec && tc < MAX_THREADS) { |
| 307 | kthread_run(async_thread, NULL, "async/%i", tc); |
| 308 | atomic_inc(&thread_count); |
| 309 | tc++; |
| 310 | } |
| 311 | |
| 312 | schedule(); |
| 313 | } |
| 314 | remove_wait_queue(&async_new, &wq); |
| 315 | |
| 316 | return 0; |
| 317 | } |
| 318 | |
| 319 | static int __init async_init(void) |
| 320 | { |
Arjan van de Ven | cdb80f6 | 2009-01-09 13:23:45 -0800 | [diff] [blame^] | 321 | if (async_enabled) |
| 322 | kthread_run(async_manager_thread, NULL, "async/mgr"); |
Arjan van de Ven | 22a9d64 | 2009-01-07 08:45:46 -0800 | [diff] [blame] | 323 | return 0; |
| 324 | } |
| 325 | |
Arjan van de Ven | cdb80f6 | 2009-01-09 13:23:45 -0800 | [diff] [blame^] | 326 | static int __init setup_async(char *str) |
| 327 | { |
| 328 | async_enabled = 1; |
| 329 | return 1; |
| 330 | } |
| 331 | |
| 332 | __setup("fastboot", setup_async); |
| 333 | |
| 334 | |
Arjan van de Ven | 22a9d64 | 2009-01-07 08:45:46 -0800 | [diff] [blame] | 335 | core_initcall(async_init); |