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 list_head *pending;
  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                 pending = &domain->pending;
  95         else
  96                 pending = &async_global_pending;
  97
  98         if (!list_empty(pending))
  99                 ret = list_first_entry(pending, struct async_entry,
 100                                        domain_list)->cookie;
 101
 102         spin_unlock_irqrestore(&async_lock, flags);
 103         return ret;
 104 }
 105
 106 /*
 107  * pick the first pending entry and run it
 108  */
 109 static void async_run_entry_fn(struct work_struct *work)
 110 {
 111         struct async_entry *entry =
 112                 container_of(work, struct async_entry, work);
 113         unsigned long flags;
 114         ktime_t uninitialized_var(calltime), delta, rettime;
 115
 116         /* 1) run (and print duration) */
 117         if (initcall_debug && system_state == SYSTEM_BOOTING) {
 118                 pr_debug("calling  %lli_%pF @ %i\n",
 119                         (long long)entry->cookie,
 120                         entry->func, task_pid_nr(current));
 121                 calltime = ktime_get();
 122         }
 123         entry->func(entry->data, entry->cookie);
 124         if (initcall_debug && system_state == SYSTEM_BOOTING) {
 125                 rettime = ktime_get();
 126                 delta = ktime_sub(rettime, calltime);
 127                 pr_debug("initcall %lli_%pF returned 0 after %lld usecs\n",
 128                         (long long)entry->cookie,
 129                         entry->func,
 130                         (long long)ktime_to_ns(delta) >> 10);
 131         }
 132
 133         /* 2) remove self from the pending queues */
 134         spin_lock_irqsave(&async_lock, flags);
 135         list_del_init(&entry->domain_list);
 136         list_del_init(&entry->global_list);
 137
 138         /* 3) free the entry */
 139         kfree(entry);
 140         atomic_dec(&entry_count);
 141
 142         spin_unlock_irqrestore(&async_lock, flags);
 143
 144         /* 4) wake up any waiters */
 145         wake_up(&async_done);
 146 }
 147
 148 static async_cookie_t __async_schedule(async_func_t func, void *data, struct async_domain *domain)
 149 {
 150         struct async_entry *entry;
 151         unsigned long flags;
 152         async_cookie_t newcookie;
 153
 154         /* allow irq-off callers */
 155         entry = kzalloc(sizeof(struct async_entry), GFP_ATOMIC);
 156
 157         /*
 158          * If we're out of memory or if there's too much work
 159          * pending already, we execute synchronously.
 160          */
 161         if (!entry || atomic_read(&entry_count) > MAX_WORK) {
 162                 kfree(entry);
 163                 spin_lock_irqsave(&async_lock, flags);
 164                 newcookie = next_cookie++;
 165                 spin_unlock_irqrestore(&async_lock, flags);
 166
 167                 /* low on memory.. run synchronously */
 168                 func(data, newcookie);
 169                 return newcookie;
 170         }
 171         INIT_LIST_HEAD(&entry->domain_list);
 172         INIT_LIST_HEAD(&entry->global_list);
 173         INIT_WORK(&entry->work, async_run_entry_fn);
 174         entry->func = func;
 175         entry->data = data;
 176         entry->domain = domain;
 177
 178         spin_lock_irqsave(&async_lock, flags);
 179
 180         /* allocate cookie and queue */
 181         newcookie = entry->cookie = next_cookie++;
 182
 183         list_add_tail(&entry->domain_list, &domain->pending);
 184         if (domain->registered)
 185                 list_add_tail(&entry->global_list, &async_global_pending);
 186
 187         atomic_inc(&entry_count);
 188         spin_unlock_irqrestore(&async_lock, flags);
 189
 190         /* mark that this task has queued an async job, used by module init */
 191         current->flags |= PF_USED_ASYNC;
 192
 193         /* schedule for execution */
 194         queue_work(system_unbound_wq, &entry->work);
 195
 196         return newcookie;
 197 }
 198
 199 /**
 200  * async_schedule - schedule a function for asynchronous execution
 201  * @func: function to execute asynchronously
 202  * @data: data pointer to pass to the function
 203  *
 204  * Returns an async_cookie_t that may be used for checkpointing later.
 205  * Note: This function may be called from atomic or non-atomic contexts.
 206  */
 207 async_cookie_t async_schedule(async_func_t func, void *data)
 208 {
 209         return __async_schedule(func, data, &async_dfl_domain);
 210 }
 211 EXPORT_SYMBOL_GPL(async_schedule);
 212
 213 /**
 214  * async_schedule_domain - schedule a function for asynchronous execution within a certain domain
 215  * @func: function to execute asynchronously
 216  * @data: data pointer to pass to the function
 217  * @domain: the domain
 218  *
 219  * Returns an async_cookie_t that may be used for checkpointing later.
 220  * @domain may be used in the async_synchronize_*_domain() functions to
 221  * wait within a certain synchronization domain rather than globally.  A
 222  * synchronization domain is specified via @domain.  Note: This function
 223  * may be called from atomic or non-atomic contexts.
 224  */
 225 async_cookie_t async_schedule_domain(async_func_t func, void *data,
 226                                      struct async_domain *domain)
 227 {
 228         return __async_schedule(func, data, domain);
 229 }
 230 EXPORT_SYMBOL_GPL(async_schedule_domain);
 231
 232 /**
 233  * async_synchronize_full - synchronize all asynchronous function calls
 234  *
 235  * This function waits until all asynchronous function calls have been done.
 236  */
 237 void async_synchronize_full(void)
 238 {
 239         async_synchronize_full_domain(NULL);
 240 }
 241 EXPORT_SYMBOL_GPL(async_synchronize_full);
 242
 243 /**
 244  * async_unregister_domain - ensure no more anonymous waiters on this domain
 245  * @domain: idle domain to flush out of any async_synchronize_full instances
 246  *
 247  * async_synchronize_{cookie|full}_domain() are not flushed since callers
 248  * of these routines should know the lifetime of @domain
 249  *
 250  * Prefer ASYNC_DOMAIN_EXCLUSIVE() declarations over flushing
 251  */
 252 void async_unregister_domain(struct async_domain *domain)
 253 {
 254         spin_lock_irq(&async_lock);
 255         WARN_ON(!domain->registered || !list_empty(&domain->pending));
 256         domain->registered = 0;
 257         spin_unlock_irq(&async_lock);
 258 }
 259 EXPORT_SYMBOL_GPL(async_unregister_domain);
 260
 261 /**
 262  * async_synchronize_full_domain - synchronize all asynchronous function within a certain domain
 263  * @domain: the domain to synchronize
 264  *
 265  * This function waits until all asynchronous function calls for the
 266  * synchronization domain specified by @domain have been done.
 267  */
 268 void async_synchronize_full_domain(struct async_domain *domain)
 269 {
 270         async_synchronize_cookie_domain(ASYNC_COOKIE_MAX, domain);
 271 }
 272 EXPORT_SYMBOL_GPL(async_synchronize_full_domain);
 273
 274 /**
 275  * async_synchronize_cookie_domain - synchronize asynchronous function calls within a certain domain with cookie checkpointing
 276  * @cookie: async_cookie_t to use as checkpoint
 277  * @domain: the domain to synchronize (%NULL for all registered domains)
 278  *
 279  * This function waits until all asynchronous function calls for the
 280  * synchronization domain specified by @domain submitted prior to @cookie
 281  * have been done.
 282  */
 283 void async_synchronize_cookie_domain(async_cookie_t cookie, struct async_domain *domain)
 284 {
 285         ktime_t uninitialized_var(starttime), delta, endtime;
 286
 287         if (initcall_debug && system_state == SYSTEM_BOOTING) {
 288                 pr_debug("async_waiting @ %i\n", task_pid_nr(current));
 289                 starttime = ktime_get();
 290         }
 291
 292         wait_event(async_done, lowest_in_progress(domain) >= cookie);
 293
 294         if (initcall_debug && system_state == SYSTEM_BOOTING) {
 295                 endtime = ktime_get();
 296                 delta = ktime_sub(endtime, starttime);
 297
 298                 pr_debug("async_continuing @ %i after %lli usec\n",
 299                         task_pid_nr(current),
 300                         (long long)ktime_to_ns(delta) >> 10);
 301         }
 302 }
 303 EXPORT_SYMBOL_GPL(async_synchronize_cookie_domain);
 304
 305 /**
 306  * async_synchronize_cookie - synchronize asynchronous function calls with cookie checkpointing
 307  * @cookie: async_cookie_t to use as checkpoint
 308  *
 309  * This function waits until all asynchronous function calls prior to @cookie
 310  * have been done.
 311  */
 312 void async_synchronize_cookie(async_cookie_t cookie)
 313 {
 314         async_synchronize_cookie_domain(cookie, &async_dfl_domain);
 315 }
 316 EXPORT_SYMBOL_GPL(async_synchronize_cookie);
 317
 318 /**
 319  * current_is_async - is %current an async worker task?
 320  *
 321  * Returns %true if %current is an async worker task.
 322  */
 323 bool current_is_async(void)
 324 {
 325         struct worker *worker = current_wq_worker();
 326
 327         return worker && worker->current_func == async_run_entry_fn;
 328 }
 329 EXPORT_SYMBOL_GPL(current_is_async);