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_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 }