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/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 62 static async_cookie_t next_cookie = 1; 63 64 #define MAX_WORK 32768 65 #define ASYNC_COOKIE_MAX ULLONG_MAX /* infinity cookie */ 66 67 static LIST_HEAD(async_global_pending); /* pending from all registered doms */ 68 static ASYNC_DOMAIN(async_dfl_domain); 69 static DEFINE_SPINLOCK(async_lock); 70 71 struct 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_ptr *func; 77 void *data; 78 struct async_domain *domain; 79 }; 80 81 static DECLARE_WAIT_QUEUE_HEAD(async_done); 82 83 static atomic_t entry_count; 84 85 static async_cookie_t lowest_in_progress(struct async_domain *domain) 86 { 87 struct async_entry *first = NULL; 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 if (!list_empty(&domain->pending)) 95 first = list_first_entry(&domain->pending, 96 struct async_entry, domain_list); 97 } else { 98 if (!list_empty(&async_global_pending)) 99 first = list_first_entry(&async_global_pending, 100 struct async_entry, global_list); 101 } 102 103 if (first) 104 ret = first->cookie; 105 106 spin_unlock_irqrestore(&async_lock, flags); 107 return ret; 108 } 109 110 /* 111 * pick the first pending entry and run it 112 */ 113 static void async_run_entry_fn(struct work_struct *work) 114 { 115 struct async_entry *entry = 116 container_of(work, struct async_entry, work); 117 unsigned long flags; 118 ktime_t uninitialized_var(calltime), delta, rettime; 119 120 /* 1) run (and print duration) */ 121 if (initcall_debug && system_state == SYSTEM_BOOTING) { 122 printk(KERN_DEBUG "calling %lli_%pF @ %i\n", 123 (long long)entry->cookie, 124 entry->func, task_pid_nr(current)); 125 calltime = ktime_get(); 126 } 127 entry->func(entry->data, entry->cookie); 128 if (initcall_debug && system_state == SYSTEM_BOOTING) { 129 rettime = ktime_get(); 130 delta = ktime_sub(rettime, calltime); 131 printk(KERN_DEBUG "initcall %lli_%pF returned 0 after %lld usecs\n", 132 (long long)entry->cookie, 133 entry->func, 134 (long long)ktime_to_ns(delta) >> 10); 135 } 136 137 /* 2) remove self from the pending queues */ 138 spin_lock_irqsave(&async_lock, flags); 139 list_del_init(&entry->domain_list); 140 list_del_init(&entry->global_list); 141 142 /* 3) free the entry */ 143 kfree(entry); 144 atomic_dec(&entry_count); 145 146 spin_unlock_irqrestore(&async_lock, flags); 147 148 /* 4) wake up any waiters */ 149 wake_up(&async_done); 150 } 151 152 static async_cookie_t __async_schedule(async_func_ptr *ptr, void *data, struct async_domain *domain) 153 { 154 struct async_entry *entry; 155 unsigned long flags; 156 async_cookie_t newcookie; 157 158 /* allow irq-off callers */ 159 entry = kzalloc(sizeof(struct async_entry), GFP_ATOMIC); 160 161 /* 162 * If we're out of memory or if there's too much work 163 * pending already, we execute synchronously. 164 */ 165 if (!entry || atomic_read(&entry_count) > MAX_WORK) { 166 kfree(entry); 167 spin_lock_irqsave(&async_lock, flags); 168 newcookie = next_cookie++; 169 spin_unlock_irqrestore(&async_lock, flags); 170 171 /* low on memory.. run synchronously */ 172 ptr(data, newcookie); 173 return newcookie; 174 } 175 INIT_WORK(&entry->work, async_run_entry_fn); 176 entry->func = ptr; 177 entry->data = data; 178 entry->domain = domain; 179 180 spin_lock_irqsave(&async_lock, flags); 181 182 /* allocate cookie and queue */ 183 newcookie = entry->cookie = next_cookie++; 184 185 list_add_tail(&entry->domain_list, &domain->pending); 186 if (domain->registered) 187 list_add_tail(&entry->global_list, &async_global_pending); 188 189 atomic_inc(&entry_count); 190 spin_unlock_irqrestore(&async_lock, flags); 191 192 /* mark that this task has queued an async job, used by module init */ 193 current->flags |= PF_USED_ASYNC; 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_dfl_domain); 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 * @domain: the domain 220 * 221 * Returns an async_cookie_t that may be used for checkpointing later. 222 * @domain may be used in the async_synchronize_*_domain() functions to 223 * wait within a certain synchronization domain rather than globally. A 224 * synchronization domain is specified via @domain. Note: This function 225 * 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 async_domain *domain) 229 { 230 return __async_schedule(ptr, data, domain); 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 async_synchronize_full_domain(NULL); 242 } 243 EXPORT_SYMBOL_GPL(async_synchronize_full); 244 245 /** 246 * async_unregister_domain - ensure no more anonymous waiters on this domain 247 * @domain: idle domain to flush out of any async_synchronize_full instances 248 * 249 * async_synchronize_{cookie|full}_domain() are not flushed since callers 250 * of these routines should know the lifetime of @domain 251 * 252 * Prefer ASYNC_DOMAIN_EXCLUSIVE() declarations over flushing 253 */ 254 void async_unregister_domain(struct async_domain *domain) 255 { 256 spin_lock_irq(&async_lock); 257 WARN_ON(!domain->registered || !list_empty(&domain->pending)); 258 domain->registered = 0; 259 spin_unlock_irq(&async_lock); 260 } 261 EXPORT_SYMBOL_GPL(async_unregister_domain); 262 263 /** 264 * async_synchronize_full_domain - synchronize all asynchronous function within a certain domain 265 * @domain: the domain to synchronize 266 * 267 * This function waits until all asynchronous function calls for the 268 * synchronization domain specified by @domain have been done. 269 */ 270 void async_synchronize_full_domain(struct async_domain *domain) 271 { 272 async_synchronize_cookie_domain(ASYNC_COOKIE_MAX, domain); 273 } 274 EXPORT_SYMBOL_GPL(async_synchronize_full_domain); 275 276 /** 277 * async_synchronize_cookie_domain - synchronize asynchronous function calls within a certain domain with cookie checkpointing 278 * @cookie: async_cookie_t to use as checkpoint 279 * @domain: the domain to synchronize (%NULL for all registered domains) 280 * 281 * This function waits until all asynchronous function calls for the 282 * synchronization domain specified by @domain submitted prior to @cookie 283 * have been done. 284 */ 285 void async_synchronize_cookie_domain(async_cookie_t cookie, struct async_domain *domain) 286 { 287 ktime_t uninitialized_var(starttime), delta, endtime; 288 289 if (initcall_debug && system_state == SYSTEM_BOOTING) { 290 printk(KERN_DEBUG "async_waiting @ %i\n", task_pid_nr(current)); 291 starttime = ktime_get(); 292 } 293 294 wait_event(async_done, lowest_in_progress(domain) >= cookie); 295 296 if (initcall_debug && system_state == SYSTEM_BOOTING) { 297 endtime = ktime_get(); 298 delta = ktime_sub(endtime, starttime); 299 300 printk(KERN_DEBUG "async_continuing @ %i after %lli usec\n", 301 task_pid_nr(current), 302 (long long)ktime_to_ns(delta) >> 10); 303 } 304 } 305 EXPORT_SYMBOL_GPL(async_synchronize_cookie_domain); 306 307 /** 308 * async_synchronize_cookie - synchronize asynchronous function calls with cookie checkpointing 309 * @cookie: async_cookie_t to use as checkpoint 310 * 311 * This function waits until all asynchronous function calls prior to @cookie 312 * have been done. 313 */ 314 void async_synchronize_cookie(async_cookie_t cookie) 315 { 316 async_synchronize_cookie_domain(cookie, &async_dfl_domain); 317 } 318 EXPORT_SYMBOL_GPL(async_synchronize_cookie); 319 320 /** 321 * current_is_async - is %current an async worker task? 322 * 323 * Returns %true if %current is an async worker task. 324 */ 325 bool current_is_async(void) 326 { 327 struct worker *worker = current_wq_worker(); 328 329 return worker && worker->current_func == async_run_entry_fn; 330 } 331