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/atomic.h> 53 #include <linux/ktime.h> 54 #include <linux/module.h> 55 #include <linux/wait.h> 56 #include <linux/sched.h> 57 #include <linux/slab.h> 58 #include <linux/workqueue.h> 59 60 static async_cookie_t next_cookie = 1; 61 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 68 struct 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 77 static DECLARE_WAIT_QUEUE_HEAD(async_done); 78 79 static atomic_t entry_count; 80 81 extern int initcall_debug; 82 83 84 /* 85 * MUST be called with the lock held! 86 */ 87 static async_cookie_t __lowest_in_progress(struct list_head *running) 88 { 89 struct async_entry *entry; 90 91 if (!list_empty(running)) { 92 entry = list_first_entry(running, 93 struct async_entry, list); 94 return entry->cookie; 95 } 96 97 list_for_each_entry(entry, &async_pending, list) 98 if (entry->running == running) 99 return entry->cookie; 100 101 return next_cookie; /* "infinity" value */ 102 } 103 104 static async_cookie_t lowest_in_progress(struct list_head *running) 105 { 106 unsigned long flags; 107 async_cookie_t ret; 108 109 spin_lock_irqsave(&async_lock, flags); 110 ret = __lowest_in_progress(running); 111 spin_unlock_irqrestore(&async_lock, flags); 112 return ret; 113 } 114 115 /* 116 * pick the first pending entry and run it 117 */ 118 static void async_run_entry_fn(struct work_struct *work) 119 { 120 struct async_entry *entry = 121 container_of(work, struct async_entry, work); 122 unsigned long flags; 123 ktime_t calltime, delta, rettime; 124 125 /* 1) move self to the running queue */ 126 spin_lock_irqsave(&async_lock, flags); 127 list_move_tail(&entry->list, entry->running); 128 spin_unlock_irqrestore(&async_lock, flags); 129 130 /* 2) run (and print duration) */ 131 if (initcall_debug && system_state == SYSTEM_BOOTING) { 132 printk(KERN_DEBUG "calling %lli_%pF @ %i\n", 133 (long long)entry->cookie, 134 entry->func, task_pid_nr(current)); 135 calltime = ktime_get(); 136 } 137 entry->func(entry->data, entry->cookie); 138 if (initcall_debug && system_state == SYSTEM_BOOTING) { 139 rettime = ktime_get(); 140 delta = ktime_sub(rettime, calltime); 141 printk(KERN_DEBUG "initcall %lli_%pF returned 0 after %lld usecs\n", 142 (long long)entry->cookie, 143 entry->func, 144 (long long)ktime_to_ns(delta) >> 10); 145 } 146 147 /* 3) remove self from the running queue */ 148 spin_lock_irqsave(&async_lock, flags); 149 list_del(&entry->list); 150 151 /* 4) free the entry */ 152 kfree(entry); 153 atomic_dec(&entry_count); 154 155 spin_unlock_irqrestore(&async_lock, flags); 156 157 /* 5) wake up any waiters */ 158 wake_up(&async_done); 159 } 160 161 static async_cookie_t __async_schedule(async_func_ptr *ptr, void *data, struct list_head *running) 162 { 163 struct async_entry *entry; 164 unsigned long flags; 165 async_cookie_t newcookie; 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 */ 174 if (!entry || atomic_read(&entry_count) > MAX_WORK) { 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 INIT_WORK(&entry->work, async_run_entry_fn); 185 entry->func = ptr; 186 entry->data = data; 187 entry->running = running; 188 189 spin_lock_irqsave(&async_lock, flags); 190 newcookie = entry->cookie = next_cookie++; 191 list_add_tail(&entry->list, &async_pending); 192 atomic_inc(&entry_count); 193 spin_unlock_irqrestore(&async_lock, flags); 194 195 /* schedule for execution */ 196 queue_work(system_unbound_wq, &entry->work); 197 198 return newcookie; 199 } 200 201 /** 202 * async_schedule - schedule a function for asynchronous execution 203 * @ptr: function to execute asynchronously 204 * @data: data pointer to pass to the function 205 * 206 * Returns an async_cookie_t that may be used for checkpointing later. 207 * Note: This function may be called from atomic or non-atomic contexts. 208 */ 209 async_cookie_t async_schedule(async_func_ptr *ptr, void *data) 210 { 211 return __async_schedule(ptr, data, &async_running); 212 } 213 EXPORT_SYMBOL_GPL(async_schedule); 214 215 /** 216 * async_schedule_domain - schedule a function for asynchronous execution within a certain domain 217 * @ptr: function to execute asynchronously 218 * @data: data pointer to pass to the function 219 * @running: running list for the domain 220 * 221 * Returns an async_cookie_t that may be used for checkpointing later. 222 * @running may be used in the async_synchronize_*_domain() functions 223 * to wait within a certain synchronization domain rather than globally. 224 * A synchronization domain is specified via the running queue @running to use. 225 * Note: This function may be called from atomic or non-atomic contexts. 226 */ 227 async_cookie_t async_schedule_domain(async_func_ptr *ptr, void *data, 228 struct list_head *running) 229 { 230 return __async_schedule(ptr, data, running); 231 } 232 EXPORT_SYMBOL_GPL(async_schedule_domain); 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 */ 239 void async_synchronize_full(void) 240 { 241 do { 242 async_synchronize_cookie(next_cookie); 243 } while (!list_empty(&async_running) || !list_empty(&async_pending)); 244 } 245 EXPORT_SYMBOL_GPL(async_synchronize_full); 246 247 /** 248 * async_synchronize_full_domain - synchronize all asynchronous function within a certain domain 249 * @list: running list to synchronize on 250 * 251 * This function waits until all asynchronous function calls for the 252 * synchronization domain specified by the running list @list have been done. 253 */ 254 void async_synchronize_full_domain(struct list_head *list) 255 { 256 async_synchronize_cookie_domain(next_cookie, list); 257 } 258 EXPORT_SYMBOL_GPL(async_synchronize_full_domain); 259 260 /** 261 * async_synchronize_cookie_domain - synchronize asynchronous function calls within a certain domain with cookie checkpointing 262 * @cookie: async_cookie_t to use as checkpoint 263 * @running: running list to synchronize on 264 * 265 * This function waits until all asynchronous function calls for the 266 * synchronization domain specified by the running list @list submitted 267 * prior to @cookie have been done. 268 */ 269 void async_synchronize_cookie_domain(async_cookie_t cookie, 270 struct list_head *running) 271 { 272 ktime_t starttime, delta, endtime; 273 274 if (initcall_debug && system_state == SYSTEM_BOOTING) { 275 printk(KERN_DEBUG "async_waiting @ %i\n", task_pid_nr(current)); 276 starttime = ktime_get(); 277 } 278 279 wait_event(async_done, lowest_in_progress(running) >= cookie); 280 281 if (initcall_debug && system_state == SYSTEM_BOOTING) { 282 endtime = ktime_get(); 283 delta = ktime_sub(endtime, starttime); 284 285 printk(KERN_DEBUG "async_continuing @ %i after %lli usec\n", 286 task_pid_nr(current), 287 (long long)ktime_to_ns(delta) >> 10); 288 } 289 } 290 EXPORT_SYMBOL_GPL(async_synchronize_cookie_domain); 291 292 /** 293 * async_synchronize_cookie - synchronize asynchronous function calls with cookie checkpointing 294 * @cookie: async_cookie_t to use as checkpoint 295 * 296 * This function waits until all asynchronous function calls prior to @cookie 297 * have been done. 298 */ 299 void async_synchronize_cookie(async_cookie_t cookie) 300 { 301 async_synchronize_cookie_domain(cookie, &async_running); 302 } 303 EXPORT_SYMBOL_GPL(async_synchronize_cookie); 304