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
  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
  66 static LIST_HEAD(async_pending);
  67 static ASYNC_DOMAIN(async_running);
  68 static LIST_HEAD(async_domains);
  69 static DEFINE_SPINLOCK(async_lock);
  70 static DEFINE_MUTEX(async_register_mutex);
  71
  72 struct async_entry {
  73         struct list_head        list;
  74         struct work_struct      work;
  75         async_cookie_t          cookie;
  76         async_func_ptr          *func;
  77         void                    *data;
  78         struct async_domain     *running;
  79 };
  80
  81 static DECLARE_WAIT_QUEUE_HEAD(async_done);
  82
  83 static atomic_t entry_count;
  84
  85
  86 /*
  87  * MUST be called with the lock held!
  88  */
  89 static async_cookie_t  __lowest_in_progress(struct async_domain *running)
  90 {
  91         async_cookie_t first_running = next_cookie;     /* infinity value */
  92         async_cookie_t first_pending = next_cookie;     /* ditto */
  93         struct async_entry *entry;
  94
  95         /*
  96          * Both running and pending lists are sorted but not disjoint.
  97          * Take the first cookies from both and return the min.
  98          */
  99         if (!list_empty(&running->domain)) {
 100                 entry = list_first_entry(&running->domain, typeof(*entry), list);
 101                 first_running = entry->cookie;
 102         }
 103
 104         list_for_each_entry(entry, &async_pending, list) {
 105                 if (entry->running == running) {
 106                         first_pending = entry->cookie;
 107                         break;
 108                 }
 109         }
 110
 111         return min(first_running, first_pending);
 112 }
 113
 114 static async_cookie_t  lowest_in_progress(struct async_domain *running)
 115 {
 116         unsigned long flags;
 117         async_cookie_t ret;
 118
 119         spin_lock_irqsave(&async_lock, flags);
 120         ret = __lowest_in_progress(running);
 121         spin_unlock_irqrestore(&async_lock, flags);
 122         return ret;
 123 }
 124
 125 /*
 126  * pick the first pending entry and run it
 127  */
 128 static void async_run_entry_fn(struct work_struct *work)
 129 {
 130         struct async_entry *entry =
 131                 container_of(work, struct async_entry, work);
 132         struct async_entry *pos;
 133         unsigned long flags;
 134         ktime_t uninitialized_var(calltime), delta, rettime;
 135         struct async_domain *running = entry->running;
 136
 137         /* 1) move self to the running queue, make sure it stays sorted */
 138         spin_lock_irqsave(&async_lock, flags);
 139         list_for_each_entry_reverse(pos, &running->domain, list)
 140                 if (entry->cookie < pos->cookie)
 141                         break;
 142         list_move_tail(&entry->list, &pos->list);
 143         spin_unlock_irqrestore(&async_lock, flags);
 144
 145         /* 2) run (and print duration) */
 146         if (initcall_debug && system_state == SYSTEM_BOOTING) {
 147                 printk(KERN_DEBUG "calling  %lli_%pF @ %i\n",
 148                         (long long)entry->cookie,
 149                         entry->func, task_pid_nr(current));
 150                 calltime = ktime_get();
 151         }
 152         entry->func(entry->data, entry->cookie);
 153         if (initcall_debug && system_state == SYSTEM_BOOTING) {
 154                 rettime = ktime_get();
 155                 delta = ktime_sub(rettime, calltime);
 156                 printk(KERN_DEBUG "initcall %lli_%pF returned 0 after %lld usecs\n",
 157                         (long long)entry->cookie,
 158                         entry->func,
 159                         (long long)ktime_to_ns(delta) >> 10);
 160         }
 161
 162         /* 3) remove self from the running queue */
 163         spin_lock_irqsave(&async_lock, flags);
 164         list_del(&entry->list);
 165         if (running->registered && --running->count == 0)
 166                 list_del_init(&running->node);
 167
 168         /* 4) free the entry */
 169         kfree(entry);
 170         atomic_dec(&entry_count);
 171
 172         spin_unlock_irqrestore(&async_lock, flags);
 173
 174         /* 5) wake up any waiters */
 175         wake_up(&async_done);
 176 }
 177
 178 static async_cookie_t __async_schedule(async_func_ptr *ptr, void *data, struct async_domain *running)
 179 {
 180         struct async_entry *entry;
 181         unsigned long flags;
 182         async_cookie_t newcookie;
 183
 184         /* allow irq-off callers */
 185         entry = kzalloc(sizeof(struct async_entry), GFP_ATOMIC);
 186
 187         /*
 188          * If we're out of memory or if there's too much work
 189          * pending already, we execute synchronously.
 190          */
 191         if (!entry || atomic_read(&entry_count) > MAX_WORK) {
 192                 kfree(entry);
 193                 spin_lock_irqsave(&async_lock, flags);
 194                 newcookie = next_cookie++;
 195                 spin_unlock_irqrestore(&async_lock, flags);
 196
 197                 /* low on memory.. run synchronously */
 198                 ptr(data, newcookie);
 199                 return newcookie;
 200         }
 201         INIT_WORK(&entry->work, async_run_entry_fn);
 202         entry->func = ptr;
 203         entry->data = data;
 204         entry->running = running;
 205
 206         spin_lock_irqsave(&async_lock, flags);
 207         newcookie = entry->cookie = next_cookie++;
 208         list_add_tail(&entry->list, &async_pending);
 209         if (running->registered && running->count++ == 0)
 210                 list_add_tail(&running->node, &async_domains);
 211         atomic_inc(&entry_count);
 212         spin_unlock_irqrestore(&async_lock, flags);
 213
 214         /* mark that this task has queued an async job, used by module init */
 215         current->flags |= PF_USED_ASYNC;
 216
 217         /* schedule for execution */
 218         queue_work(system_unbound_wq, &entry->work);
 219
 220         return newcookie;
 221 }
 222
 223 /**
 224  * async_schedule - schedule a function for asynchronous execution
 225  * @ptr: function to execute asynchronously
 226  * @data: data pointer to pass to the function
 227  *
 228  * Returns an async_cookie_t that may be used for checkpointing later.
 229  * Note: This function may be called from atomic or non-atomic contexts.
 230  */
 231 async_cookie_t async_schedule(async_func_ptr *ptr, void *data)
 232 {
 233         return __async_schedule(ptr, data, &async_running);
 234 }
 235 EXPORT_SYMBOL_GPL(async_schedule);
 236
 237 /**
 238  * async_schedule_domain - schedule a function for asynchronous execution within a certain domain
 239  * @ptr: function to execute asynchronously
 240  * @data: data pointer to pass to the function
 241  * @running: running list for the domain
 242  *
 243  * Returns an async_cookie_t that may be used for checkpointing later.
 244  * @running may be used in the async_synchronize_*_domain() functions
 245  * to wait within a certain synchronization domain rather than globally.
 246  * A synchronization domain is specified via the running queue @running to use.
 247  * Note: This function may be called from atomic or non-atomic contexts.
 248  */
 249 async_cookie_t async_schedule_domain(async_func_ptr *ptr, void *data,
 250                                      struct async_domain *running)
 251 {
 252         return __async_schedule(ptr, data, running);
 253 }
 254 EXPORT_SYMBOL_GPL(async_schedule_domain);
 255
 256 /**
 257  * async_synchronize_full - synchronize all asynchronous function calls
 258  *
 259  * This function waits until all asynchronous function calls have been done.
 260  */
 261 void async_synchronize_full(void)
 262 {
 263         mutex_lock(&async_register_mutex);
 264         do {
 265                 struct async_domain *domain = NULL;
 266
 267                 spin_lock_irq(&async_lock);
 268                 if (!list_empty(&async_domains))
 269                         domain = list_first_entry(&async_domains, typeof(*domain), node);
 270                 spin_unlock_irq(&async_lock);
 271
 272                 async_synchronize_cookie_domain(next_cookie, domain);
 273         } while (!list_empty(&async_domains));
 274         mutex_unlock(&async_register_mutex);
 275 }
 276 EXPORT_SYMBOL_GPL(async_synchronize_full);
 277
 278 /**
 279  * async_unregister_domain - ensure no more anonymous waiters on this domain
 280  * @domain: idle domain to flush out of any async_synchronize_full instances
 281  *
 282  * async_synchronize_{cookie|full}_domain() are not flushed since callers
 283  * of these routines should know the lifetime of @domain
 284  *
 285  * Prefer ASYNC_DOMAIN_EXCLUSIVE() declarations over flushing
 286  */
 287 void async_unregister_domain(struct async_domain *domain)
 288 {
 289         mutex_lock(&async_register_mutex);
 290         spin_lock_irq(&async_lock);
 291         WARN_ON(!domain->registered || !list_empty(&domain->node) ||
 292                 !list_empty(&domain->domain));
 293         domain->registered = 0;
 294         spin_unlock_irq(&async_lock);
 295         mutex_unlock(&async_register_mutex);
 296 }
 297 EXPORT_SYMBOL_GPL(async_unregister_domain);
 298
 299 /**
 300  * async_synchronize_full_domain - synchronize all asynchronous function within a certain domain
 301  * @domain: running list to synchronize on
 302  *
 303  * This function waits until all asynchronous function calls for the
 304  * synchronization domain specified by the running list @domain have been done.
 305  */
 306 void async_synchronize_full_domain(struct async_domain *domain)
 307 {
 308         async_synchronize_cookie_domain(next_cookie, domain);
 309 }
 310 EXPORT_SYMBOL_GPL(async_synchronize_full_domain);
 311
 312 /**
 313  * async_synchronize_cookie_domain - synchronize asynchronous function calls within a certain domain with cookie checkpointing
 314  * @cookie: async_cookie_t to use as checkpoint
 315  * @running: running list to synchronize on
 316  *
 317  * This function waits until all asynchronous function calls for the
 318  * synchronization domain specified by running list @running submitted
 319  * prior to @cookie have been done.
 320  */
 321 void async_synchronize_cookie_domain(async_cookie_t cookie, struct async_domain *running)
 322 {
 323         ktime_t uninitialized_var(starttime), delta, endtime;
 324
 325         if (!running)
 326                 return;
 327
 328         if (initcall_debug && system_state == SYSTEM_BOOTING) {
 329                 printk(KERN_DEBUG "async_waiting @ %i\n", task_pid_nr(current));
 330                 starttime = ktime_get();
 331         }
 332
 333         wait_event(async_done, lowest_in_progress(running) >= cookie);
 334
 335         if (initcall_debug && system_state == SYSTEM_BOOTING) {
 336                 endtime = ktime_get();
 337                 delta = ktime_sub(endtime, starttime);
 338
 339                 printk(KERN_DEBUG "async_continuing @ %i after %lli usec\n",
 340                         task_pid_nr(current),
 341                         (long long)ktime_to_ns(delta) >> 10);
 342         }
 343 }
 344 EXPORT_SYMBOL_GPL(async_synchronize_cookie_domain);
 345
 346 /**
 347  * async_synchronize_cookie - synchronize asynchronous function calls with cookie checkpointing
 348  * @cookie: async_cookie_t to use as checkpoint
 349  *
 350  * This function waits until all asynchronous function calls prior to @cookie
 351  * have been done.
 352  */
 353 void async_synchronize_cookie(async_cookie_t cookie)
 354 {
 355         async_synchronize_cookie_domain(cookie, &async_running);
 356 }
 357 EXPORT_SYMBOL_GPL(async_synchronize_cookie);
 358
 359 /**
 360  * current_is_async - is %current an async worker task?
 361  *
 362  * Returns %true if %current is an async worker task.
 363  */
 364 bool current_is_async(void)
 365 {
 366         struct worker *worker = current_wq_worker();
 367
 368         return worker && worker->current_func == async_run_entry_fn;
 369 }