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 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 (!running) { /* just check the entry count */
  92                 if (atomic_read(&entry_count))
  93                         return 0; /* smaller than any cookie */
  94                 else
  95                         return next_cookie;
  96         }
  97
  98         if (!list_empty(running)) {
  99                 entry = list_first_entry(running,
 100                         struct async_entry, list);
 101                 return entry->cookie;
 102         }
 103
 104         list_for_each_entry(entry, &async_pending, list)
 105                 if (entry->running == running)
 106                         return entry->cookie;
 107
 108         return next_cookie;     /* "infinity" value */
 109 }
 110
 111 static async_cookie_t  lowest_in_progress(struct list_head *running)
 112 {
 113         unsigned long flags;
 114         async_cookie_t ret;
 115
 116         spin_lock_irqsave(&async_lock, flags);
 117         ret = __lowest_in_progress(running);
 118         spin_unlock_irqrestore(&async_lock, flags);
 119         return ret;
 120 }
 121
 122 /*
 123  * pick the first pending entry and run it
 124  */
 125 static void async_run_entry_fn(struct work_struct *work)
 126 {
 127         struct async_entry *entry =
 128                 container_of(work, struct async_entry, work);
 129         unsigned long flags;
 130         ktime_t uninitialized_var(calltime), delta, rettime;
 131
 132         /* 1) move self to the running queue */
 133         spin_lock_irqsave(&async_lock, flags);
 134         list_move_tail(&entry->list, entry->running);
 135         spin_unlock_irqrestore(&async_lock, flags);
 136
 137         /* 2) run (and print duration) */
 138         if (initcall_debug && system_state == SYSTEM_BOOTING) {
 139                 printk(KERN_DEBUG "calling  %lli_%pF @ %i\n",
 140                         (long long)entry->cookie,
 141                         entry->func, task_pid_nr(current));
 142                 calltime = ktime_get();
 143         }
 144         entry->func(entry->data, entry->cookie);
 145         if (initcall_debug && system_state == SYSTEM_BOOTING) {
 146                 rettime = ktime_get();
 147                 delta = ktime_sub(rettime, calltime);
 148                 printk(KERN_DEBUG "initcall %lli_%pF returned 0 after %lld usecs\n",
 149                         (long long)entry->cookie,
 150                         entry->func,
 151                         (long long)ktime_to_ns(delta) >> 10);
 152         }
 153
 154         /* 3) remove self from the running queue */
 155         spin_lock_irqsave(&async_lock, flags);
 156         list_del(&entry->list);
 157
 158         /* 4) free the entry */
 159         kfree(entry);
 160         atomic_dec(&entry_count);
 161
 162         spin_unlock_irqrestore(&async_lock, flags);
 163
 164         /* 5) wake up any waiters */
 165         wake_up(&async_done);
 166 }
 167
 168 static async_cookie_t __async_schedule(async_func_ptr *ptr, void *data, struct list_head *running)
 169 {
 170         struct async_entry *entry;
 171         unsigned long flags;
 172         async_cookie_t newcookie;
 173
 174         /* allow irq-off callers */
 175         entry = kzalloc(sizeof(struct async_entry), GFP_ATOMIC);
 176
 177         /*
 178          * If we're out of memory or if there's too much work
 179          * pending already, we execute synchronously.
 180          */
 181         if (!entry || atomic_read(&entry_count) > MAX_WORK) {
 182                 kfree(entry);
 183                 spin_lock_irqsave(&async_lock, flags);
 184                 newcookie = next_cookie++;
 185                 spin_unlock_irqrestore(&async_lock, flags);
 186
 187                 /* low on memory.. run synchronously */
 188                 ptr(data, newcookie);
 189                 return newcookie;
 190         }
 191         INIT_WORK(&entry->work, async_run_entry_fn);
 192         entry->func = ptr;
 193         entry->data = data;
 194         entry->running = running;
 195
 196         spin_lock_irqsave(&async_lock, flags);
 197         newcookie = entry->cookie = next_cookie++;
 198         list_add_tail(&entry->list, &async_pending);
 199         atomic_inc(&entry_count);
 200         spin_unlock_irqrestore(&async_lock, flags);
 201
 202         /* schedule for execution */
 203         queue_work(system_unbound_wq, &entry->work);
 204
 205         return newcookie;
 206 }
 207
 208 /**
 209  * async_schedule - schedule a function for asynchronous execution
 210  * @ptr: function to execute asynchronously
 211  * @data: data pointer to pass to the function
 212  *
 213  * Returns an async_cookie_t that may be used for checkpointing later.
 214  * Note: This function may be called from atomic or non-atomic contexts.
 215  */
 216 async_cookie_t async_schedule(async_func_ptr *ptr, void *data)
 217 {
 218         return __async_schedule(ptr, data, &async_running);
 219 }
 220 EXPORT_SYMBOL_GPL(async_schedule);
 221
 222 /**
 223  * async_schedule_domain - schedule a function for asynchronous execution within a certain domain
 224  * @ptr: function to execute asynchronously
 225  * @data: data pointer to pass to the function
 226  * @running: running list for the domain
 227  *
 228  * Returns an async_cookie_t that may be used for checkpointing later.
 229  * @running may be used in the async_synchronize_*_domain() functions
 230  * to wait within a certain synchronization domain rather than globally.
 231  * A synchronization domain is specified via the running queue @running to use.
 232  * Note: This function may be called from atomic or non-atomic contexts.
 233  */
 234 async_cookie_t async_schedule_domain(async_func_ptr *ptr, void *data,
 235                                      struct list_head *running)
 236 {
 237         return __async_schedule(ptr, data, running);
 238 }
 239 EXPORT_SYMBOL_GPL(async_schedule_domain);
 240
 241 /**
 242  * async_synchronize_full - synchronize all asynchronous function calls
 243  *
 244  * This function waits until all asynchronous function calls have been done.
 245  */
 246 void async_synchronize_full(void)
 247 {
 248         async_synchronize_cookie_domain(next_cookie, NULL);
 249 }
 250 EXPORT_SYMBOL_GPL(async_synchronize_full);
 251
 252 /**
 253  * async_synchronize_full_domain - synchronize all asynchronous function within a certain domain
 254  * @list: running list to synchronize on
 255  *
 256  * This function waits until all asynchronous function calls for the
 257  * synchronization domain specified by the running list @list have been done.
 258  */
 259 void async_synchronize_full_domain(struct list_head *list)
 260 {
 261         async_synchronize_cookie_domain(next_cookie, list);
 262 }
 263 EXPORT_SYMBOL_GPL(async_synchronize_full_domain);
 264
 265 /**
 266  * async_synchronize_cookie_domain - synchronize asynchronous function calls within a certain domain with cookie checkpointing
 267  * @cookie: async_cookie_t to use as checkpoint
 268  * @running: running list to synchronize on, NULL indicates all lists
 269  *
 270  * This function waits until all asynchronous function calls for the
 271  * synchronization domain specified by the running list @list submitted
 272  * prior to @cookie have been done.
 273  */
 274 void async_synchronize_cookie_domain(async_cookie_t cookie,
 275                                      struct list_head *running)
 276 {
 277         ktime_t uninitialized_var(starttime), delta, endtime;
 278
 279         if (initcall_debug && system_state == SYSTEM_BOOTING) {
 280                 printk(KERN_DEBUG "async_waiting @ %i\n", task_pid_nr(current));
 281                 starttime = ktime_get();
 282         }
 283
 284         wait_event(async_done, lowest_in_progress(running) >= cookie);
 285
 286         if (initcall_debug && system_state == SYSTEM_BOOTING) {
 287                 endtime = ktime_get();
 288                 delta = ktime_sub(endtime, starttime);
 289
 290                 printk(KERN_DEBUG "async_continuing @ %i after %lli usec\n",
 291                         task_pid_nr(current),
 292                         (long long)ktime_to_ns(delta) >> 10);
 293         }
 294 }
 295 EXPORT_SYMBOL_GPL(async_synchronize_cookie_domain);
 296
 297 /**
 298  * async_synchronize_cookie - synchronize asynchronous function calls with cookie checkpointing
 299  * @cookie: async_cookie_t to use as checkpoint
 300  *
 301  * This function waits until all asynchronous function calls prior to @cookie
 302  * have been done.
 303  */
 304 void async_synchronize_cookie(async_cookie_t cookie)
 305 {
 306         async_synchronize_cookie_domain(cookie, &async_running);
 307 }
 308 EXPORT_SYMBOL_GPL(async_synchronize_cookie);