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
  82 /*
  83  * MUST be called with the lock held!
  84  */
  85 static async_cookie_t  __lowest_in_progress(struct list_head *running)
  86 {
  87         struct async_entry *entry;
  88
  89         if (!list_empty(running)) {
  90                 entry = list_first_entry(running,
  91                         struct async_entry, list);
  92                 return entry->cookie;
  93         }
  94
  95         list_for_each_entry(entry, &async_pending, list)
  96                 if (entry->running == running)
  97                         return entry->cookie;
  98
  99         return next_cookie;     /* "infinity" value */
 100 }
 101
 102 static async_cookie_t  lowest_in_progress(struct list_head *running)
 103 {
 104         unsigned long flags;
 105         async_cookie_t ret;
 106
 107         spin_lock_irqsave(&async_lock, flags);
 108         ret = __lowest_in_progress(running);
 109         spin_unlock_irqrestore(&async_lock, flags);
 110         return ret;
 111 }
 112
 113 /*
 114  * pick the first pending entry and run it
 115  */
 116 static void async_run_entry_fn(struct work_struct *work)
 117 {
 118         struct async_entry *entry =
 119                 container_of(work, struct async_entry, work);
 120         unsigned long flags;
 121         ktime_t uninitialized_var(calltime), delta, rettime;
 122
 123         /* 1) move self to the running queue */
 124         spin_lock_irqsave(&async_lock, flags);
 125         list_move_tail(&entry->list, entry->running);
 126         spin_unlock_irqrestore(&async_lock, flags);
 127
 128         /* 2) run (and print duration) */
 129         if (initcall_debug && system_state == SYSTEM_BOOTING) {
 130                 printk(KERN_DEBUG "calling  %lli_%pF @ %i\n",
 131                         (long long)entry->cookie,
 132                         entry->func, task_pid_nr(current));
 133                 calltime = ktime_get();
 134         }
 135         entry->func(entry->data, entry->cookie);
 136         if (initcall_debug && system_state == SYSTEM_BOOTING) {
 137                 rettime = ktime_get();
 138                 delta = ktime_sub(rettime, calltime);
 139                 printk(KERN_DEBUG "initcall %lli_%pF returned 0 after %lld usecs\n",
 140                         (long long)entry->cookie,
 141                         entry->func,
 142                         (long long)ktime_to_ns(delta) >> 10);
 143         }
 144
 145         /* 3) remove self from the running queue */
 146         spin_lock_irqsave(&async_lock, flags);
 147         list_del(&entry->list);
 148
 149         /* 4) free the entry */
 150         kfree(entry);
 151         atomic_dec(&entry_count);
 152
 153         spin_unlock_irqrestore(&async_lock, flags);
 154
 155         /* 5) wake up any waiters */
 156         wake_up(&async_done);
 157 }
 158
 159 static async_cookie_t __async_schedule(async_func_ptr *ptr, void *data, struct list_head *running)
 160 {
 161         struct async_entry *entry;
 162         unsigned long flags;
 163         async_cookie_t newcookie;
 164
 165         /* allow irq-off callers */
 166         entry = kzalloc(sizeof(struct async_entry), GFP_ATOMIC);
 167
 168         /*
 169          * If we're out of memory or if there's too much work
 170          * pending already, we execute synchronously.
 171          */
 172         if (!entry || atomic_read(&entry_count) > MAX_WORK) {
 173                 kfree(entry);
 174                 spin_lock_irqsave(&async_lock, flags);
 175                 newcookie = next_cookie++;
 176                 spin_unlock_irqrestore(&async_lock, flags);
 177
 178                 /* low on memory.. run synchronously */
 179                 ptr(data, newcookie);
 180                 return newcookie;
 181         }
 182         INIT_WORK(&entry->work, async_run_entry_fn);
 183         entry->func = ptr;
 184         entry->data = data;
 185         entry->running = running;
 186
 187         spin_lock_irqsave(&async_lock, flags);
 188         newcookie = entry->cookie = next_cookie++;
 189         list_add_tail(&entry->list, &async_pending);
 190         atomic_inc(&entry_count);
 191         spin_unlock_irqrestore(&async_lock, flags);
 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  * @ptr: 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_ptr *ptr, void *data)
 208 {
 209         return __async_schedule(ptr, data, &async_running);
 210 }
 211 EXPORT_SYMBOL_GPL(async_schedule);
 212
 213 /**
 214  * async_schedule_domain - schedule a function for asynchronous execution within a certain domain
 215  * @ptr: function to execute asynchronously
 216  * @data: data pointer to pass to the function
 217  * @running: running list for the domain
 218  *
 219  * Returns an async_cookie_t that may be used for checkpointing later.
 220  * @running may be used in the async_synchronize_*_domain() functions
 221  * to wait within a certain synchronization domain rather than globally.
 222  * A synchronization domain is specified via the running queue @running to use.
 223  * Note: This function may be called from atomic or non-atomic contexts.
 224  */
 225 async_cookie_t async_schedule_domain(async_func_ptr *ptr, void *data,
 226                                      struct list_head *running)
 227 {
 228         return __async_schedule(ptr, data, running);
 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         do {
 240                 async_synchronize_cookie(next_cookie);
 241         } while (!list_empty(&async_running) || !list_empty(&async_pending));
 242 }
 243 EXPORT_SYMBOL_GPL(async_synchronize_full);
 244
 245 /**
 246  * async_synchronize_full_domain - synchronize all asynchronous function within a certain domain
 247  * @list: running list to synchronize on
 248  *
 249  * This function waits until all asynchronous function calls for the
 250  * synchronization domain specified by the running list @list have been done.
 251  */
 252 void async_synchronize_full_domain(struct list_head *list)
 253 {
 254         async_synchronize_cookie_domain(next_cookie, list);
 255 }
 256 EXPORT_SYMBOL_GPL(async_synchronize_full_domain);
 257
 258 /**
 259  * async_synchronize_cookie_domain - synchronize asynchronous function calls within a certain domain with cookie checkpointing
 260  * @cookie: async_cookie_t to use as checkpoint
 261  * @running: running list to synchronize on
 262  *
 263  * This function waits until all asynchronous function calls for the
 264  * synchronization domain specified by the running list @list submitted
 265  * prior to @cookie have been done.
 266  */
 267 void async_synchronize_cookie_domain(async_cookie_t cookie,
 268                                      struct list_head *running)
 269 {
 270         ktime_t uninitialized_var(starttime), delta, endtime;
 271
 272         if (initcall_debug && system_state == SYSTEM_BOOTING) {
 273                 printk(KERN_DEBUG "async_waiting @ %i\n", task_pid_nr(current));
 274                 starttime = ktime_get();
 275         }
 276
 277         wait_event(async_done, lowest_in_progress(running) >= cookie);
 278
 279         if (initcall_debug && system_state == SYSTEM_BOOTING) {
 280                 endtime = ktime_get();
 281                 delta = ktime_sub(endtime, starttime);
 282
 283                 printk(KERN_DEBUG "async_continuing @ %i after %lli usec\n",
 284                         task_pid_nr(current),
 285                         (long long)ktime_to_ns(delta) >> 10);
 286         }
 287 }
 288 EXPORT_SYMBOL_GPL(async_synchronize_cookie_domain);
 289
 290 /**
 291  * async_synchronize_cookie - synchronize asynchronous function calls with cookie checkpointing
 292  * @cookie: async_cookie_t to use as checkpoint
 293  *
 294  * This function waits until all asynchronous function calls prior to @cookie
 295  * have been done.
 296  */
 297 void async_synchronize_cookie(async_cookie_t cookie)
 298 {
 299         async_synchronize_cookie_domain(cookie, &async_running);
 300 }
 301 EXPORT_SYMBOL_GPL(async_synchronize_cookie);