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 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_RUNNING) {
 122                 pr_debug("calling  %lli_%pS @ %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_RUNNING) {
 129                 rettime = ktime_get();
 130                 delta = ktime_sub(rettime, calltime);
 131                 pr_debug("initcall %lli_%pS 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 /**
 153  * async_schedule_node_domain - NUMA specific version of async_schedule_domain
 154  * @func: function to execute asynchronously
 155  * @data: data pointer to pass to the function
 156  * @node: NUMA node that we want to schedule this on or close to
 157  * @domain: the domain
 158  *
 159  * Returns an async_cookie_t that may be used for checkpointing later.
 160  * @domain may be used in the async_synchronize_*_domain() functions to
 161  * wait within a certain synchronization domain rather than globally.
 162  *
 163  * Note: This function may be called from atomic or non-atomic contexts.
 164  *
 165  * The node requested will be honored on a best effort basis. If the node
 166  * has no CPUs associated with it then the work is distributed among all
 167  * available CPUs.
 168  */
 169 async_cookie_t async_schedule_node_domain(async_func_t func, void *data,
 170                                           int node, struct async_domain *domain)
 171 {
 172         struct async_entry *entry;
 173         unsigned long flags;
 174         async_cookie_t newcookie;
 175
 176         /* allow irq-off callers */
 177         entry = kzalloc(sizeof(struct async_entry), GFP_ATOMIC);
 178
 179         /*
 180          * If we're out of memory or if there's too much work
 181          * pending already, we execute synchronously.
 182          */
 183         if (!entry || atomic_read(&entry_count) > MAX_WORK) {
 184                 kfree(entry);
 185                 spin_lock_irqsave(&async_lock, flags);
 186                 newcookie = next_cookie++;
 187                 spin_unlock_irqrestore(&async_lock, flags);
 188
 189                 /* low on memory.. run synchronously */
 190                 func(data, newcookie);
 191                 return newcookie;
 192         }
 193         INIT_LIST_HEAD(&entry->domain_list);
 194         INIT_LIST_HEAD(&entry->global_list);
 195         INIT_WORK(&entry->work, async_run_entry_fn);
 196         entry->func = func;
 197         entry->data = data;
 198         entry->domain = domain;
 199
 200         spin_lock_irqsave(&async_lock, flags);
 201
 202         /* allocate cookie and queue */
 203         newcookie = entry->cookie = next_cookie++;
 204
 205         list_add_tail(&entry->domain_list, &domain->pending);
 206         if (domain->registered)
 207                 list_add_tail(&entry->global_list, &async_global_pending);
 208
 209         atomic_inc(&entry_count);
 210         spin_unlock_irqrestore(&async_lock, flags);
 211
 212         /* mark that this task has queued an async job, used by module init */
 213         current->flags |= PF_USED_ASYNC;
 214
 215         /* schedule for execution */
 216         queue_work_node(node, system_unbound_wq, &entry->work);
 217
 218         return newcookie;
 219 }
 220 EXPORT_SYMBOL_GPL(async_schedule_node_domain);
 221
 222 /**
 223  * async_schedule_node - NUMA specific version of async_schedule
 224  * @func: function to execute asynchronously
 225  * @data: data pointer to pass to the function
 226  * @node: NUMA node that we want to schedule this on or close to
 227  *
 228  * Returns an async_cookie_t that may be used for checkpointing later.
 229  * Note: This function may be called from atomic or non-atomic contexts.
 230  *
 231  * The node requested will be honored on a best effort basis. If the node
 232  * has no CPUs associated with it then the work is distributed among all
 233  * available CPUs.
 234  */
 235 async_cookie_t async_schedule_node(async_func_t func, void *data, int node)
 236 {
 237         return async_schedule_node_domain(func, data, node, &async_dfl_domain);
 238 }
 239 EXPORT_SYMBOL_GPL(async_schedule_node);
 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_full_domain(NULL);
 249 }
 250 EXPORT_SYMBOL_GPL(async_synchronize_full);
 251
 252 /**
 253  * async_unregister_domain - ensure no more anonymous waiters on this domain
 254  * @domain: idle domain to flush out of any async_synchronize_full instances
 255  *
 256  * async_synchronize_{cookie|full}_domain() are not flushed since callers
 257  * of these routines should know the lifetime of @domain
 258  *
 259  * Prefer ASYNC_DOMAIN_EXCLUSIVE() declarations over flushing
 260  */
 261 void async_unregister_domain(struct async_domain *domain)
 262 {
 263         spin_lock_irq(&async_lock);
 264         WARN_ON(!domain->registered || !list_empty(&domain->pending));
 265         domain->registered = 0;
 266         spin_unlock_irq(&async_lock);
 267 }
 268 EXPORT_SYMBOL_GPL(async_unregister_domain);
 269
 270 /**
 271  * async_synchronize_full_domain - synchronize all asynchronous function within a certain domain
 272  * @domain: the domain to synchronize
 273  *
 274  * This function waits until all asynchronous function calls for the
 275  * synchronization domain specified by @domain have been done.
 276  */
 277 void async_synchronize_full_domain(struct async_domain *domain)
 278 {
 279         async_synchronize_cookie_domain(ASYNC_COOKIE_MAX, domain);
 280 }
 281 EXPORT_SYMBOL_GPL(async_synchronize_full_domain);
 282
 283 /**
 284  * async_synchronize_cookie_domain - synchronize asynchronous function calls within a certain domain with cookie checkpointing
 285  * @cookie: async_cookie_t to use as checkpoint
 286  * @domain: the domain to synchronize (%NULL for all registered domains)
 287  *
 288  * This function waits until all asynchronous function calls for the
 289  * synchronization domain specified by @domain submitted prior to @cookie
 290  * have been done.
 291  */
 292 void async_synchronize_cookie_domain(async_cookie_t cookie, struct async_domain *domain)
 293 {
 294         ktime_t uninitialized_var(starttime), delta, endtime;
 295
 296         if (initcall_debug && system_state < SYSTEM_RUNNING) {
 297                 pr_debug("async_waiting @ %i\n", task_pid_nr(current));
 298                 starttime = ktime_get();
 299         }
 300
 301         wait_event(async_done, lowest_in_progress(domain) >= cookie);
 302
 303         if (initcall_debug && system_state < SYSTEM_RUNNING) {
 304                 endtime = ktime_get();
 305                 delta = ktime_sub(endtime, starttime);
 306
 307                 pr_debug("async_continuing @ %i after %lli usec\n",
 308                         task_pid_nr(current),
 309                         (long long)ktime_to_ns(delta) >> 10);
 310         }
 311 }
 312 EXPORT_SYMBOL_GPL(async_synchronize_cookie_domain);
 313
 314 /**
 315  * async_synchronize_cookie - synchronize asynchronous function calls with cookie checkpointing
 316  * @cookie: async_cookie_t to use as checkpoint
 317  *
 318  * This function waits until all asynchronous function calls prior to @cookie
 319  * have been done.
 320  */
 321 void async_synchronize_cookie(async_cookie_t cookie)
 322 {
 323         async_synchronize_cookie_domain(cookie, &async_dfl_domain);
 324 }
 325 EXPORT_SYMBOL_GPL(async_synchronize_cookie);
 326
 327 /**
 328  * current_is_async - is %current an async worker task?
 329  *
 330  * Returns %true if %current is an async worker task.
 331  */
 332 bool current_is_async(void)
 333 {
 334         struct worker *worker = current_wq_worker();
 335
 336         return worker && worker->current_func == async_run_entry_fn;
 337 }
 338 EXPORT_SYMBOL_GPL(current_is_async);