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 #define ASYNC_COOKIE_MAX        ULLONG_MAX      /* infinity cookie */
  66
  67 static LIST_HEAD(async_pending);
  68 static ASYNC_DOMAIN(async_dfl_domain);
  69 static LIST_HEAD(async_domains);
  70 static DEFINE_SPINLOCK(async_lock);
  71 static DEFINE_MUTEX(async_register_mutex);
  72
  73 struct async_entry {
  74         struct list_head        list;
  75         struct work_struct      work;
  76         async_cookie_t          cookie;
  77         async_func_ptr          *func;
  78         void                    *data;
  79         struct async_domain     *domain;
  80 };
  81
  82 static DECLARE_WAIT_QUEUE_HEAD(async_done);
  83
  84 static atomic_t entry_count;
  85
  86
  87 /*
  88  * MUST be called with the lock held!
  89  */
  90 static async_cookie_t __lowest_in_progress(struct async_domain *domain)
  91 {
  92         async_cookie_t first_running = ASYNC_COOKIE_MAX;
  93         async_cookie_t first_pending = ASYNC_COOKIE_MAX;
  94         struct async_entry *entry;
  95
  96         /*
  97          * Both running and pending lists are sorted but not disjoint.
  98          * Take the first cookies from both and return the min.
  99          */
 100         if (!list_empty(&domain->running)) {
 101                 entry = list_first_entry(&domain->running, typeof(*entry), list);
 102                 first_running = entry->cookie;
 103         }
 104
 105         list_for_each_entry(entry, &async_pending, list) {
 106                 if (entry->domain == domain) {
 107                         first_pending = entry->cookie;
 108                         break;
 109                 }
 110         }
 111
 112         return min(first_running, first_pending);
 113 }
 114
 115 static async_cookie_t lowest_in_progress(struct async_domain *domain)
 116 {
 117         unsigned long flags;
 118         async_cookie_t ret;
 119
 120         spin_lock_irqsave(&async_lock, flags);
 121         ret = __lowest_in_progress(domain);
 122         spin_unlock_irqrestore(&async_lock, flags);
 123         return ret;
 124 }
 125
 126 /*
 127  * pick the first pending entry and run it
 128  */
 129 static void async_run_entry_fn(struct work_struct *work)
 130 {
 131         struct async_entry *entry =
 132                 container_of(work, struct async_entry, work);
 133         struct async_entry *pos;
 134         unsigned long flags;
 135         ktime_t uninitialized_var(calltime), delta, rettime;
 136         struct async_domain *domain = entry->domain;
 137
 138         /* 1) move self to the running queue, make sure it stays sorted */
 139         spin_lock_irqsave(&async_lock, flags);
 140         list_for_each_entry_reverse(pos, &domain->running, list)
 141                 if (entry->cookie < pos->cookie)
 142                         break;
 143         list_move_tail(&entry->list, &pos->list);
 144         spin_unlock_irqrestore(&async_lock, flags);
 145
 146         /* 2) run (and print duration) */
 147         if (initcall_debug && system_state == SYSTEM_BOOTING) {
 148                 printk(KERN_DEBUG "calling  %lli_%pF @ %i\n",
 149                         (long long)entry->cookie,
 150                         entry->func, task_pid_nr(current));
 151                 calltime = ktime_get();
 152         }
 153         entry->func(entry->data, entry->cookie);
 154         if (initcall_debug && system_state == SYSTEM_BOOTING) {
 155                 rettime = ktime_get();
 156                 delta = ktime_sub(rettime, calltime);
 157                 printk(KERN_DEBUG "initcall %lli_%pF returned 0 after %lld usecs\n",
 158                         (long long)entry->cookie,
 159                         entry->func,
 160                         (long long)ktime_to_ns(delta) >> 10);
 161         }
 162
 163         /* 3) remove self from the running queue */
 164         spin_lock_irqsave(&async_lock, flags);
 165         list_del(&entry->list);
 166         if (domain->registered && --domain->count == 0)
 167                 list_del_init(&domain->node);
 168
 169         /* 4) free the entry */
 170         kfree(entry);
 171         atomic_dec(&entry_count);
 172
 173         spin_unlock_irqrestore(&async_lock, flags);
 174
 175         /* 5) wake up any waiters */
 176         wake_up(&async_done);
 177 }
 178
 179 static async_cookie_t __async_schedule(async_func_ptr *ptr, void *data, struct async_domain *domain)
 180 {
 181         struct async_entry *entry;
 182         unsigned long flags;
 183         async_cookie_t newcookie;
 184
 185         /* allow irq-off callers */
 186         entry = kzalloc(sizeof(struct async_entry), GFP_ATOMIC);
 187
 188         /*
 189          * If we're out of memory or if there's too much work
 190          * pending already, we execute synchronously.
 191          */
 192         if (!entry || atomic_read(&entry_count) > MAX_WORK) {
 193                 kfree(entry);
 194                 spin_lock_irqsave(&async_lock, flags);
 195                 newcookie = next_cookie++;
 196                 spin_unlock_irqrestore(&async_lock, flags);
 197
 198                 /* low on memory.. run synchronously */
 199                 ptr(data, newcookie);
 200                 return newcookie;
 201         }
 202         INIT_WORK(&entry->work, async_run_entry_fn);
 203         entry->func = ptr;
 204         entry->data = data;
 205         entry->domain = domain;
 206
 207         spin_lock_irqsave(&async_lock, flags);
 208         newcookie = entry->cookie = next_cookie++;
 209         list_add_tail(&entry->list, &async_pending);
 210         if (domain->registered && domain->count++ == 0)
 211                 list_add_tail(&domain->node, &async_domains);
 212         atomic_inc(&entry_count);
 213         spin_unlock_irqrestore(&async_lock, flags);
 214
 215         /* mark that this task has queued an async job, used by module init */
 216         current->flags |= PF_USED_ASYNC;
 217
 218         /* schedule for execution */
 219         queue_work(system_unbound_wq, &entry->work);
 220
 221         return newcookie;
 222 }
 223
 224 /**
 225  * async_schedule - schedule a function for asynchronous execution
 226  * @ptr: function to execute asynchronously
 227  * @data: data pointer to pass to the function
 228  *
 229  * Returns an async_cookie_t that may be used for checkpointing later.
 230  * Note: This function may be called from atomic or non-atomic contexts.
 231  */
 232 async_cookie_t async_schedule(async_func_ptr *ptr, void *data)
 233 {
 234         return __async_schedule(ptr, data, &async_dfl_domain);
 235 }
 236 EXPORT_SYMBOL_GPL(async_schedule);
 237
 238 /**
 239  * async_schedule_domain - schedule a function for asynchronous execution within a certain domain
 240  * @ptr: function to execute asynchronously
 241  * @data: data pointer to pass to the function
 242  * @domain: the domain
 243  *
 244  * Returns an async_cookie_t that may be used for checkpointing later.
 245  * @domain may be used in the async_synchronize_*_domain() functions to
 246  * wait within a certain synchronization domain rather than globally.  A
 247  * synchronization domain is specified via @domain.  Note: This function
 248  * may be called from atomic or non-atomic contexts.
 249  */
 250 async_cookie_t async_schedule_domain(async_func_ptr *ptr, void *data,
 251                                      struct async_domain *domain)
 252 {
 253         return __async_schedule(ptr, data, domain);
 254 }
 255 EXPORT_SYMBOL_GPL(async_schedule_domain);
 256
 257 /**
 258  * async_synchronize_full - synchronize all asynchronous function calls
 259  *
 260  * This function waits until all asynchronous function calls have been done.
 261  */
 262 void async_synchronize_full(void)
 263 {
 264         mutex_lock(&async_register_mutex);
 265         do {
 266                 struct async_domain *domain = NULL;
 267
 268                 spin_lock_irq(&async_lock);
 269                 if (!list_empty(&async_domains))
 270                         domain = list_first_entry(&async_domains, typeof(*domain), node);
 271                 spin_unlock_irq(&async_lock);
 272
 273                 async_synchronize_cookie_domain(ASYNC_COOKIE_MAX, domain);
 274         } while (!list_empty(&async_domains));
 275         mutex_unlock(&async_register_mutex);
 276 }
 277 EXPORT_SYMBOL_GPL(async_synchronize_full);
 278
 279 /**
 280  * async_unregister_domain - ensure no more anonymous waiters on this domain
 281  * @domain: idle domain to flush out of any async_synchronize_full instances
 282  *
 283  * async_synchronize_{cookie|full}_domain() are not flushed since callers
 284  * of these routines should know the lifetime of @domain
 285  *
 286  * Prefer ASYNC_DOMAIN_EXCLUSIVE() declarations over flushing
 287  */
 288 void async_unregister_domain(struct async_domain *domain)
 289 {
 290         mutex_lock(&async_register_mutex);
 291         spin_lock_irq(&async_lock);
 292         WARN_ON(!domain->registered || !list_empty(&domain->node) ||
 293                 !list_empty(&domain->running));
 294         domain->registered = 0;
 295         spin_unlock_irq(&async_lock);
 296         mutex_unlock(&async_register_mutex);
 297 }
 298 EXPORT_SYMBOL_GPL(async_unregister_domain);
 299
 300 /**
 301  * async_synchronize_full_domain - synchronize all asynchronous function within a certain domain
 302  * @domain: the domain to synchronize
 303  *
 304  * This function waits until all asynchronous function calls for the
 305  * synchronization domain specified by @domain have been done.
 306  */
 307 void async_synchronize_full_domain(struct async_domain *domain)
 308 {
 309         async_synchronize_cookie_domain(ASYNC_COOKIE_MAX, domain);
 310 }
 311 EXPORT_SYMBOL_GPL(async_synchronize_full_domain);
 312
 313 /**
 314  * async_synchronize_cookie_domain - synchronize asynchronous function calls within a certain domain with cookie checkpointing
 315  * @cookie: async_cookie_t to use as checkpoint
 316  * @domain: the domain to synchronize
 317  *
 318  * This function waits until all asynchronous function calls for the
 319  * synchronization domain specified by @domain submitted prior to @cookie
 320  * have been done.
 321  */
 322 void async_synchronize_cookie_domain(async_cookie_t cookie, struct async_domain *domain)
 323 {
 324         ktime_t uninitialized_var(starttime), delta, endtime;
 325
 326         if (!domain)
 327                 return;
 328
 329         if (initcall_debug && system_state == SYSTEM_BOOTING) {
 330                 printk(KERN_DEBUG "async_waiting @ %i\n", task_pid_nr(current));
 331                 starttime = ktime_get();
 332         }
 333
 334         wait_event(async_done, lowest_in_progress(domain) >= cookie);
 335
 336         if (initcall_debug && system_state == SYSTEM_BOOTING) {
 337                 endtime = ktime_get();
 338                 delta = ktime_sub(endtime, starttime);
 339
 340                 printk(KERN_DEBUG "async_continuing @ %i after %lli usec\n",
 341                         task_pid_nr(current),
 342                         (long long)ktime_to_ns(delta) >> 10);
 343         }
 344 }
 345 EXPORT_SYMBOL_GPL(async_synchronize_cookie_domain);
 346
 347 /**
 348  * async_synchronize_cookie - synchronize asynchronous function calls with cookie checkpointing
 349  * @cookie: async_cookie_t to use as checkpoint
 350  *
 351  * This function waits until all asynchronous function calls prior to @cookie
 352  * have been done.
 353  */
 354 void async_synchronize_cookie(async_cookie_t cookie)
 355 {
 356         async_synchronize_cookie_domain(cookie, &async_dfl_domain);
 357 }
 358 EXPORT_SYMBOL_GPL(async_synchronize_cookie);
 359
 360 /**
 361  * current_is_async - is %current an async worker task?
 362  *
 363  * Returns %true if %current is an async worker task.
 364  */
 365 bool current_is_async(void)
 366 {
 367         struct worker *worker = current_wq_worker();
 368
 369         return worker && worker->current_func == async_run_entry_fn;
 370 }