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_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_t            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_RUNNING) {
 122                 pr_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_RUNNING) {
 129                 rettime = ktime_get();
 130                 delta = ktime_sub(rettime, calltime);
 131                 pr_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_t func, 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                 func(data, newcookie);
 173                 return newcookie;
 174         }
 175         INIT_LIST_HEAD(&entry->domain_list);
 176         INIT_LIST_HEAD(&entry->global_list);
 177         INIT_WORK(&entry->work, async_run_entry_fn);
 178         entry->func = func;
 179         entry->data = data;
 180         entry->domain = domain;
 181
 182         spin_lock_irqsave(&async_lock, flags);
 183
 184         /* allocate cookie and queue */
 185         newcookie = entry->cookie = next_cookie++;
 186
 187         list_add_tail(&entry->domain_list, &domain->pending);
 188         if (domain->registered)
 189                 list_add_tail(&entry->global_list, &async_global_pending);
 190
 191         atomic_inc(&entry_count);
 192         spin_unlock_irqrestore(&async_lock, flags);
 193
 194         /* mark that this task has queued an async job, used by module init */
 195         current->flags |= PF_USED_ASYNC;
 196
 197         /* schedule for execution */
 198         queue_work(system_unbound_wq, &entry->work);
 199
 200         return newcookie;
 201 }
 202
 203 /**
 204  * async_schedule - schedule a function for asynchronous execution
 205  * @func: function to execute asynchronously
 206  * @data: data pointer to pass to the function
 207  *
 208  * Returns an async_cookie_t that may be used for checkpointing later.
 209  * Note: This function may be called from atomic or non-atomic contexts.
 210  */
 211 async_cookie_t async_schedule(async_func_t func, void *data)
 212 {
 213         return __async_schedule(func, data, &async_dfl_domain);
 214 }
 215 EXPORT_SYMBOL_GPL(async_schedule);
 216
 217 /**
 218  * async_schedule_domain - schedule a function for asynchronous execution within a certain domain
 219  * @func: function to execute asynchronously
 220  * @data: data pointer to pass to the function
 221  * @domain: the domain
 222  *
 223  * Returns an async_cookie_t that may be used for checkpointing later.
 224  * @domain may be used in the async_synchronize_*_domain() functions to
 225  * wait within a certain synchronization domain rather than globally.  A
 226  * synchronization domain is specified via @domain.  Note: This function
 227  * may be called from atomic or non-atomic contexts.
 228  */
 229 async_cookie_t async_schedule_domain(async_func_t func, void *data,
 230                                      struct async_domain *domain)
 231 {
 232         return __async_schedule(func, data, domain);
 233 }
 234 EXPORT_SYMBOL_GPL(async_schedule_domain);
 235
 236 /**
 237  * async_synchronize_full - synchronize all asynchronous function calls
 238  *
 239  * This function waits until all asynchronous function calls have been done.
 240  */
 241 void async_synchronize_full(void)
 242 {
 243         async_synchronize_full_domain(NULL);
 244 }
 245 EXPORT_SYMBOL_GPL(async_synchronize_full);
 246
 247 /**
 248  * async_unregister_domain - ensure no more anonymous waiters on this domain
 249  * @domain: idle domain to flush out of any async_synchronize_full instances
 250  *
 251  * async_synchronize_{cookie|full}_domain() are not flushed since callers
 252  * of these routines should know the lifetime of @domain
 253  *
 254  * Prefer ASYNC_DOMAIN_EXCLUSIVE() declarations over flushing
 255  */
 256 void async_unregister_domain(struct async_domain *domain)
 257 {
 258         spin_lock_irq(&async_lock);
 259         WARN_ON(!domain->registered || !list_empty(&domain->pending));
 260         domain->registered = 0;
 261         spin_unlock_irq(&async_lock);
 262 }
 263 EXPORT_SYMBOL_GPL(async_unregister_domain);
 264
 265 /**
 266  * async_synchronize_full_domain - synchronize all asynchronous function within a certain domain
 267  * @domain: the domain to synchronize
 268  *
 269  * This function waits until all asynchronous function calls for the
 270  * synchronization domain specified by @domain have been done.
 271  */
 272 void async_synchronize_full_domain(struct async_domain *domain)
 273 {
 274         async_synchronize_cookie_domain(ASYNC_COOKIE_MAX, domain);
 275 }
 276 EXPORT_SYMBOL_GPL(async_synchronize_full_domain);
 277
 278 /**
 279  * async_synchronize_cookie_domain - synchronize asynchronous function calls within a certain domain with cookie checkpointing
 280  * @cookie: async_cookie_t to use as checkpoint
 281  * @domain: the domain to synchronize (%NULL for all registered domains)
 282  *
 283  * This function waits until all asynchronous function calls for the
 284  * synchronization domain specified by @domain submitted prior to @cookie
 285  * have been done.
 286  */
 287 void async_synchronize_cookie_domain(async_cookie_t cookie, struct async_domain *domain)
 288 {
 289         ktime_t uninitialized_var(starttime), delta, endtime;
 290
 291         if (initcall_debug && system_state < SYSTEM_RUNNING) {
 292                 pr_debug("async_waiting @ %i\n", task_pid_nr(current));
 293                 starttime = ktime_get();
 294         }
 295
 296         wait_event(async_done, lowest_in_progress(domain) >= cookie);
 297
 298         if (initcall_debug && system_state < SYSTEM_RUNNING) {
 299                 endtime = ktime_get();
 300                 delta = ktime_sub(endtime, starttime);
 301
 302                 pr_debug("async_continuing @ %i after %lli usec\n",
 303                         task_pid_nr(current),
 304                         (long long)ktime_to_ns(delta) >> 10);
 305         }
 306 }
 307 EXPORT_SYMBOL_GPL(async_synchronize_cookie_domain);
 308
 309 /**
 310  * async_synchronize_cookie - synchronize asynchronous function calls with cookie checkpointing
 311  * @cookie: async_cookie_t to use as checkpoint
 312  *
 313  * This function waits until all asynchronous function calls prior to @cookie
 314  * have been done.
 315  */
 316 void async_synchronize_cookie(async_cookie_t cookie)
 317 {
 318         async_synchronize_cookie_domain(cookie, &async_dfl_domain);
 319 }
 320 EXPORT_SYMBOL_GPL(async_synchronize_cookie);
 321
 322 /**
 323  * current_is_async - is %current an async worker task?
 324  *
 325  * Returns %true if %current is an async worker task.
 326  */
 327 bool current_is_async(void)
 328 {
 329         struct worker *worker = current_wq_worker();
 330
 331         return worker && worker->current_func == async_run_entry_fn;
 332 }
 333 EXPORT_SYMBOL_GPL(current_is_async);