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/module.h>
  55 #include <linux/wait.h>
  56 #include <linux/sched.h>
  57 #include <linux/slab.h>
  58 #include <linux/workqueue.h>
  59
  60 static async_cookie_t next_cookie = 1;
  61
  62 #define MAX_WORK        32768
  63
  64 static LIST_HEAD(async_pending);
  65 static LIST_HEAD(async_running);
  66 static DEFINE_SPINLOCK(async_lock);
  67
  68 struct async_entry {
  69         struct list_head        list;
  70         struct work_struct      work;
  71         async_cookie_t          cookie;
  72         async_func_ptr          *func;
  73         void                    *data;
  74         struct list_head        *running;
  75 };
  76
  77 static DECLARE_WAIT_QUEUE_HEAD(async_done);
  78
  79 static atomic_t entry_count;
  80
  81 extern int initcall_debug;
  82
  83
  84 /*
  85  * MUST be called with the lock held!
  86  */
  87 static async_cookie_t  __lowest_in_progress(struct list_head *running)
  88 {
  89         struct async_entry *entry;
  90
  91         if (!list_empty(running)) {
  92                 entry = list_first_entry(running,
  93                         struct async_entry, list);
  94                 return entry->cookie;
  95         }
  96
  97         list_for_each_entry(entry, &async_pending, list)
  98                 if (entry->running == running)
  99                         return entry->cookie;
 100
 101         return next_cookie;     /* "infinity" value */
 102 }
 103
 104 static async_cookie_t  lowest_in_progress(struct list_head *running)
 105 {
 106         unsigned long flags;
 107         async_cookie_t ret;
 108
 109         spin_lock_irqsave(&async_lock, flags);
 110         ret = __lowest_in_progress(running);
 111         spin_unlock_irqrestore(&async_lock, flags);
 112         return ret;
 113 }
 114
 115 /*
 116  * pick the first pending entry and run it
 117  */
 118 static void async_run_entry_fn(struct work_struct *work)
 119 {
 120         struct async_entry *entry =
 121                 container_of(work, struct async_entry, work);
 122         unsigned long flags;
 123         ktime_t calltime, delta, rettime;
 124
 125         /* 1) move self to the running queue */
 126         spin_lock_irqsave(&async_lock, flags);
 127         list_move_tail(&entry->list, entry->running);
 128         spin_unlock_irqrestore(&async_lock, flags);
 129
 130         /* 2) run (and print duration) */
 131         if (initcall_debug && system_state == SYSTEM_BOOTING) {
 132                 printk(KERN_DEBUG "calling  %lli_%pF @ %i\n",
 133                         (long long)entry->cookie,
 134                         entry->func, task_pid_nr(current));
 135                 calltime = ktime_get();
 136         }
 137         entry->func(entry->data, entry->cookie);
 138         if (initcall_debug && system_state == SYSTEM_BOOTING) {
 139                 rettime = ktime_get();
 140                 delta = ktime_sub(rettime, calltime);
 141                 printk(KERN_DEBUG "initcall %lli_%pF returned 0 after %lld usecs\n",
 142                         (long long)entry->cookie,
 143                         entry->func,
 144                         (long long)ktime_to_ns(delta) >> 10);
 145         }
 146
 147         /* 3) remove self from the running queue */
 148         spin_lock_irqsave(&async_lock, flags);
 149         list_del(&entry->list);
 150
 151         /* 4) free the entry */
 152         kfree(entry);
 153         atomic_dec(&entry_count);
 154
 155         spin_unlock_irqrestore(&async_lock, flags);
 156
 157         /* 5) wake up any waiters */
 158         wake_up(&async_done);
 159 }
 160
 161 static async_cookie_t __async_schedule(async_func_ptr *ptr, void *data, struct list_head *running)
 162 {
 163         struct async_entry *entry;
 164         unsigned long flags;
 165         async_cookie_t newcookie;
 166
 167         /* allow irq-off callers */
 168         entry = kzalloc(sizeof(struct async_entry), GFP_ATOMIC);
 169
 170         /*
 171          * If we're out of memory or if there's too much work
 172          * pending already, we execute synchronously.
 173          */
 174         if (!entry || atomic_read(&entry_count) > MAX_WORK) {
 175                 kfree(entry);
 176                 spin_lock_irqsave(&async_lock, flags);
 177                 newcookie = next_cookie++;
 178                 spin_unlock_irqrestore(&async_lock, flags);
 179
 180                 /* low on memory.. run synchronously */
 181                 ptr(data, newcookie);
 182                 return newcookie;
 183         }
 184         INIT_WORK(&entry->work, async_run_entry_fn);
 185         entry->func = ptr;
 186         entry->data = data;
 187         entry->running = running;
 188
 189         spin_lock_irqsave(&async_lock, flags);
 190         newcookie = entry->cookie = next_cookie++;
 191         list_add_tail(&entry->list, &async_pending);
 192         atomic_inc(&entry_count);
 193         spin_unlock_irqrestore(&async_lock, flags);
 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_running);
 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  * @running: running list for the domain
 220  *
 221  * Returns an async_cookie_t that may be used for checkpointing later.
 222  * @running may be used in the async_synchronize_*_domain() functions
 223  * to wait within a certain synchronization domain rather than globally.
 224  * A synchronization domain is specified via the running queue @running to use.
 225  * Note: This function 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 list_head *running)
 229 {
 230         return __async_schedule(ptr, data, running);
 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         do {
 242                 async_synchronize_cookie(next_cookie);
 243         } while (!list_empty(&async_running) || !list_empty(&async_pending));
 244 }
 245 EXPORT_SYMBOL_GPL(async_synchronize_full);
 246
 247 /**
 248  * async_synchronize_full_domain - synchronize all asynchronous function within a certain domain
 249  * @list: running list to synchronize on
 250  *
 251  * This function waits until all asynchronous function calls for the
 252  * synchronization domain specified by the running list @list have been done.
 253  */
 254 void async_synchronize_full_domain(struct list_head *list)
 255 {
 256         async_synchronize_cookie_domain(next_cookie, list);
 257 }
 258 EXPORT_SYMBOL_GPL(async_synchronize_full_domain);
 259
 260 /**
 261  * async_synchronize_cookie_domain - synchronize asynchronous function calls within a certain domain with cookie checkpointing
 262  * @cookie: async_cookie_t to use as checkpoint
 263  * @running: running list to synchronize on
 264  *
 265  * This function waits until all asynchronous function calls for the
 266  * synchronization domain specified by the running list @list submitted
 267  * prior to @cookie have been done.
 268  */
 269 void async_synchronize_cookie_domain(async_cookie_t cookie,
 270                                      struct list_head *running)
 271 {
 272         ktime_t starttime, delta, endtime;
 273
 274         if (initcall_debug && system_state == SYSTEM_BOOTING) {
 275                 printk(KERN_DEBUG "async_waiting @ %i\n", task_pid_nr(current));
 276                 starttime = ktime_get();
 277         }
 278
 279         wait_event(async_done, lowest_in_progress(running) >= cookie);
 280
 281         if (initcall_debug && system_state == SYSTEM_BOOTING) {
 282                 endtime = ktime_get();
 283                 delta = ktime_sub(endtime, starttime);
 284
 285                 printk(KERN_DEBUG "async_continuing @ %i after %lli usec\n",
 286                         task_pid_nr(current),
 287                         (long long)ktime_to_ns(delta) >> 10);
 288         }
 289 }
 290 EXPORT_SYMBOL_GPL(async_synchronize_cookie_domain);
 291
 292 /**
 293  * async_synchronize_cookie - synchronize asynchronous function calls with cookie checkpointing
 294  * @cookie: async_cookie_t to use as checkpoint
 295  *
 296  * This function waits until all asynchronous function calls prior to @cookie
 297  * have been done.
 298  */
 299 void async_synchronize_cookie(async_cookie_t cookie)
 300 {
 301         async_synchronize_cookie_domain(cookie, &async_running);
 302 }
 303 EXPORT_SYMBOL_GPL(async_synchronize_cookie);