linux/kernel/async.c
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   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
  16Goals and Theory of Operation
  17
  18The primary goal of this feature is to reduce the kernel boot time,
  19by doing various independent hardware delays and discovery operations
  20decoupled and not strictly serialized.
  21
  22More specifically, the asynchronous function call concept allows
  23certain operations (primarily during system boot) to happen
  24asynchronously, out of order, while these operations still
  25have their externally visible parts happen sequentially and in-order.
  26(not unlike how out-of-order CPUs retire their instructions in order)
  27
  28Key to the asynchronous function call implementation is the concept of
  29a "sequence cookie" (which, although it has an abstracted type, can be
  30thought of as a monotonically incrementing number).
  31
  32The async core will assign each scheduled event such a sequence cookie and
  33pass this to the called functions.
  34
  35The asynchronously called function should before doing a globally visible
  36operation, such as registering device numbers, call the
  37async_synchronize_cookie() function and pass in its own cookie. The
  38async_synchronize_cookie() function will make sure that all asynchronous
  39operations that were scheduled prior to the operation corresponding with the
  40cookie have completed.
  41
  42Subsystem/driver initialization code that scheduled asynchronous probe
  43functions, but which shares global resources with other drivers/subsystems
  44that do not use the asynchronous call feature, need to do a full
  45synchronization with the async_synchronize_full() function, before returning
  46from their init function. This is to maintain strict ordering between the
  47asynchronous 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
  60static async_cookie_t next_cookie = 1;
  61
  62#define MAX_WORK        32768
  63
  64static LIST_HEAD(async_pending);
  65static LIST_HEAD(async_running);
  66static DEFINE_SPINLOCK(async_lock);
  67
  68struct 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
  77static DECLARE_WAIT_QUEUE_HEAD(async_done);
  78
  79static atomic_t entry_count;
  80
  81
  82/*
  83 * MUST be called with the lock held!
  84 */
  85static async_cookie_t  __lowest_in_progress(struct list_head *running)
  86{
  87        struct async_entry *entry;
  88
  89        if (!running) { /* just check the entry count */
  90                if (atomic_read(&entry_count))
  91                        return 0; /* smaller than any cookie */
  92                else
  93                        return next_cookie;
  94        }
  95
  96        if (!list_empty(running)) {
  97                entry = list_first_entry(running,
  98                        struct async_entry, list);
  99                return entry->cookie;
 100        }
 101
 102        list_for_each_entry(entry, &async_pending, list)
 103                if (entry->running == running)
 104                        return entry->cookie;
 105
 106        return next_cookie;     /* "infinity" value */
 107}
 108
 109static async_cookie_t  lowest_in_progress(struct list_head *running)
 110{
 111        unsigned long flags;
 112        async_cookie_t ret;
 113
 114        spin_lock_irqsave(&async_lock, flags);
 115        ret = __lowest_in_progress(running);
 116        spin_unlock_irqrestore(&async_lock, flags);
 117        return ret;
 118}
 119
 120/*
 121 * pick the first pending entry and run it
 122 */
 123static void async_run_entry_fn(struct work_struct *work)
 124{
 125        struct async_entry *entry =
 126                container_of(work, struct async_entry, work);
 127        unsigned long flags;
 128        ktime_t uninitialized_var(calltime), delta, rettime;
 129
 130        /* 1) move self to the running queue */
 131        spin_lock_irqsave(&async_lock, flags);
 132        list_move_tail(&entry->list, entry->running);
 133        spin_unlock_irqrestore(&async_lock, flags);
 134
 135        /* 2) run (and print duration) */
 136        if (initcall_debug && system_state == SYSTEM_BOOTING) {
 137                printk(KERN_DEBUG "calling  %lli_%pF @ %i\n",
 138                        (long long)entry->cookie,
 139                        entry->func, task_pid_nr(current));
 140                calltime = ktime_get();
 141        }
 142        entry->func(entry->data, entry->cookie);
 143        if (initcall_debug && system_state == SYSTEM_BOOTING) {
 144                rettime = ktime_get();
 145                delta = ktime_sub(rettime, calltime);
 146                printk(KERN_DEBUG "initcall %lli_%pF returned 0 after %lld usecs\n",
 147                        (long long)entry->cookie,
 148                        entry->func,
 149                        (long long)ktime_to_ns(delta) >> 10);
 150        }
 151
 152        /* 3) remove self from the running queue */
 153        spin_lock_irqsave(&async_lock, flags);
 154        list_del(&entry->list);
 155
 156        /* 4) free the entry */
 157        kfree(entry);
 158        atomic_dec(&entry_count);
 159
 160        spin_unlock_irqrestore(&async_lock, flags);
 161
 162        /* 5) wake up any waiters */
 163        wake_up(&async_done);
 164}
 165
 166static async_cookie_t __async_schedule(async_func_ptr *ptr, void *data, struct list_head *running)
 167{
 168        struct async_entry *entry;
 169        unsigned long flags;
 170        async_cookie_t newcookie;
 171
 172        /* allow irq-off callers */
 173        entry = kzalloc(sizeof(struct async_entry), GFP_ATOMIC);
 174
 175        /*
 176         * If we're out of memory or if there's too much work
 177         * pending already, we execute synchronously.
 178         */
 179        if (!entry || atomic_read(&entry_count) > MAX_WORK) {
 180                kfree(entry);
 181                spin_lock_irqsave(&async_lock, flags);
 182                newcookie = next_cookie++;
 183                spin_unlock_irqrestore(&async_lock, flags);
 184
 185                /* low on memory.. run synchronously */
 186                ptr(data, newcookie);
 187                return newcookie;
 188        }
 189        INIT_WORK(&entry->work, async_run_entry_fn);
 190        entry->func = ptr;
 191        entry->data = data;
 192        entry->running = running;
 193
 194        spin_lock_irqsave(&async_lock, flags);
 195        newcookie = entry->cookie = next_cookie++;
 196        list_add_tail(&entry->list, &async_pending);
 197        atomic_inc(&entry_count);
 198        spin_unlock_irqrestore(&async_lock, flags);
 199
 200        /* schedule for execution */
 201        queue_work(system_unbound_wq, &entry->work);
 202
 203        return newcookie;
 204}
 205
 206/**
 207 * async_schedule - schedule a function for asynchronous execution
 208 * @ptr: function to execute asynchronously
 209 * @data: data pointer to pass to the function
 210 *
 211 * Returns an async_cookie_t that may be used for checkpointing later.
 212 * Note: This function may be called from atomic or non-atomic contexts.
 213 */
 214async_cookie_t async_schedule(async_func_ptr *ptr, void *data)
 215{
 216        return __async_schedule(ptr, data, &async_running);
 217}
 218EXPORT_SYMBOL_GPL(async_schedule);
 219
 220/**
 221 * async_schedule_domain - schedule a function for asynchronous execution within a certain domain
 222 * @ptr: function to execute asynchronously
 223 * @data: data pointer to pass to the function
 224 * @running: running list for the domain
 225 *
 226 * Returns an async_cookie_t that may be used for checkpointing later.
 227 * @running may be used in the async_synchronize_*_domain() functions
 228 * to wait within a certain synchronization domain rather than globally.
 229 * A synchronization domain is specified via the running queue @running to use.
 230 * Note: This function may be called from atomic or non-atomic contexts.
 231 */
 232async_cookie_t async_schedule_domain(async_func_ptr *ptr, void *data,
 233                                     struct list_head *running)
 234{
 235        return __async_schedule(ptr, data, running);
 236}
 237EXPORT_SYMBOL_GPL(async_schedule_domain);
 238
 239/**
 240 * async_synchronize_full - synchronize all asynchronous function calls
 241 *
 242 * This function waits until all asynchronous function calls have been done.
 243 */
 244void async_synchronize_full(void)
 245{
 246        async_synchronize_cookie_domain(next_cookie, NULL);
 247}
 248EXPORT_SYMBOL_GPL(async_synchronize_full);
 249
 250/**
 251 * async_synchronize_full_domain - synchronize all asynchronous function within a certain domain
 252 * @list: running list to synchronize on
 253 *
 254 * This function waits until all asynchronous function calls for the
 255 * synchronization domain specified by the running list @list have been done.
 256 */
 257void async_synchronize_full_domain(struct list_head *list)
 258{
 259        async_synchronize_cookie_domain(next_cookie, list);
 260}
 261EXPORT_SYMBOL_GPL(async_synchronize_full_domain);
 262
 263/**
 264 * async_synchronize_cookie_domain - synchronize asynchronous function calls within a certain domain with cookie checkpointing
 265 * @cookie: async_cookie_t to use as checkpoint
 266 * @running: running list to synchronize on, NULL indicates all lists
 267 *
 268 * This function waits until all asynchronous function calls for the
 269 * synchronization domain specified by the running list @list submitted
 270 * prior to @cookie have been done.
 271 */
 272void async_synchronize_cookie_domain(async_cookie_t cookie,
 273                                     struct list_head *running)
 274{
 275        ktime_t uninitialized_var(starttime), delta, endtime;
 276
 277        if (initcall_debug && system_state == SYSTEM_BOOTING) {
 278                printk(KERN_DEBUG "async_waiting @ %i\n", task_pid_nr(current));
 279                starttime = ktime_get();
 280        }
 281
 282        wait_event(async_done, lowest_in_progress(running) >= cookie);
 283
 284        if (initcall_debug && system_state == SYSTEM_BOOTING) {
 285                endtime = ktime_get();
 286                delta = ktime_sub(endtime, starttime);
 287
 288                printk(KERN_DEBUG "async_continuing @ %i after %lli usec\n",
 289                        task_pid_nr(current),
 290                        (long long)ktime_to_ns(delta) >> 10);
 291        }
 292}
 293EXPORT_SYMBOL_GPL(async_synchronize_cookie_domain);
 294
 295/**
 296 * async_synchronize_cookie - synchronize asynchronous function calls with cookie checkpointing
 297 * @cookie: async_cookie_t to use as checkpoint
 298 *
 299 * This function waits until all asynchronous function calls prior to @cookie
 300 * have been done.
 301 */
 302void async_synchronize_cookie(async_cookie_t cookie)
 303{
 304        async_synchronize_cookie_domain(cookie, &async_running);
 305}
 306EXPORT_SYMBOL_GPL(async_synchronize_cookie);
 307
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