kernel/async.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * async.c: Asynchronous function calls for boot performance
   4  *
   5  * (C) Copyright 2009 Intel Corporation
   6  * Author: Arjan van de Ven <arjan@linux.intel.com>
   7  */
   8
   9
  10 /*
  11
  12 Goals and Theory of Operation
  13
  14 The primary goal of this feature is to reduce the kernel boot time,
  15 by doing various independent hardware delays and discovery operations
  16 decoupled and not strictly serialized.
  17
  18 More specifically, the asynchronous function call concept allows
  19 certain operations (primarily during system boot) to happen
  20 asynchronously, out of order, while these operations still
  21 have their externally visible parts happen sequentially and in-order.
  22 (not unlike how out-of-order CPUs retire their instructions in order)
  23
  24 Key to the asynchronous function call implementation is the concept of
  25 a "sequence cookie" (which, although it has an abstracted type, can be
  26 thought of as a monotonically incrementing number).
  27
  28 The async core will assign each scheduled event such a sequence cookie and
  29 pass this to the called functions.
  30
  31 The asynchronously called function should before doing a globally visible
  32 operation, such as registering device numbers, call the
  33 async_synchronize_cookie() function and pass in its own cookie. The
  34 async_synchronize_cookie() function will make sure that all asynchronous
  35 operations that were scheduled prior to the operation corresponding with the
  36 cookie have completed.
  37
  38 Subsystem/driver initialization code that scheduled asynchronous probe
  39 functions, but which shares global resources with other drivers/subsystems
  40 that do not use the asynchronous call feature, need to do a full
  41 synchronization with the async_synchronize_full() function, before returning
  42 from their init function. This is to maintain strict ordering between the
  43 asynchronous and synchronous parts of the kernel.
  44
  45 */
  46
  47 #include <linux/async.h>
  48 #include <linux/atomic.h>
  49 #include <linux/export.h>
  50 #include <linux/ktime.h>
  51 #include <linux/pid.h>
  52 #include <linux/sched.h>
  53 #include <linux/slab.h>
  54 #include <linux/wait.h>
  55 #include <linux/workqueue.h>
  56
  57 #include "workqueue_internal.h"
  58
  59 static async_cookie_t next_cookie = 1;
  60
  61 #define MAX_WORK                32768
  62 #define ASYNC_COOKIE_MAX        ULLONG_MAX      /* infinity cookie */
  63
  64 static LIST_HEAD(async_global_pending); /* pending from all registered doms */
  65 static ASYNC_DOMAIN(async_dfl_domain);
  66 static DEFINE_SPINLOCK(async_lock);
  67 static struct workqueue_struct *async_wq;
  68
  69 struct async_entry {
  70         struct list_head        domain_list;
  71         struct list_head        global_list;
  72         struct work_struct      work;
  73         async_cookie_t          cookie;
  74         async_func_t            func;
  75         void                    *data;
  76         struct async_domain     *domain;
  77 };
  78
  79 static DECLARE_WAIT_QUEUE_HEAD(async_done);
  80
  81 static atomic_t entry_count;
  82
  83 static long long microseconds_since(ktime_t start)
  84 {
  85         ktime_t now = ktime_get();
  86         return ktime_to_ns(ktime_sub(now, start)) >> 10;
  87 }
  88
  89 static async_cookie_t lowest_in_progress(struct async_domain *domain)
  90 {
  91         struct async_entry *first = NULL;
  92         async_cookie_t ret = ASYNC_COOKIE_MAX;
  93         unsigned long flags;
  94
  95         spin_lock_irqsave(&async_lock, flags);
  96
  97         if (domain) {
  98                 if (!list_empty(&domain->pending))
  99                         first = list_first_entry(&domain->pending,
 100                                         struct async_entry, domain_list);
 101         } else {
 102                 if (!list_empty(&async_global_pending))
 103                         first = list_first_entry(&async_global_pending,
 104                                         struct async_entry, global_list);
 105         }
 106
 107         if (first)
 108                 ret = first->cookie;
 109
 110         spin_unlock_irqrestore(&async_lock, flags);
 111         return ret;
 112 }
 113
 114 /*
 115  * pick the first pending entry and run it
 116  */
 117 static void async_run_entry_fn(struct work_struct *work)
 118 {
 119         struct async_entry *entry =
 120                 container_of(work, struct async_entry, work);
 121         unsigned long flags;
 122         ktime_t calltime;
 123
 124         /* 1) run (and print duration) */
 125         pr_debug("calling  %lli_%pS @ %i\n", (long long)entry->cookie,
 126                  entry->func, task_pid_nr(current));
 127         calltime = ktime_get();
 128
 129         entry->func(entry->data, entry->cookie);
 130
 131         pr_debug("initcall %lli_%pS returned after %lld usecs\n",
 132                  (long long)entry->cookie, entry->func,
 133                  microseconds_since(calltime));
 134
 135         /* 2) remove self from the pending queues */
 136         spin_lock_irqsave(&async_lock, flags);
 137         list_del_init(&entry->domain_list);
 138         list_del_init(&entry->global_list);
 139
 140         /* 3) free the entry */
 141         kfree(entry);
 142         atomic_dec(&entry_count);
 143
 144         spin_unlock_irqrestore(&async_lock, flags);
 145
 146         /* 4) wake up any waiters */
 147         wake_up(&async_done);
 148 }
 149
 150 static async_cookie_t __async_schedule_node_domain(async_func_t func,
 151                                                    void *data, int node,
 152                                                    struct async_domain *domain,
 153                                                    struct async_entry *entry)
 154 {
 155         async_cookie_t newcookie;
 156         unsigned long flags;
 157
 158         INIT_LIST_HEAD(&entry->domain_list);
 159         INIT_LIST_HEAD(&entry->global_list);
 160         INIT_WORK(&entry->work, async_run_entry_fn);
 161         entry->func = func;
 162         entry->data = data;
 163         entry->domain = domain;
 164
 165         spin_lock_irqsave(&async_lock, flags);
 166
 167         /* allocate cookie and queue */
 168         newcookie = entry->cookie = next_cookie++;
 169
 170         list_add_tail(&entry->domain_list, &domain->pending);
 171         if (domain->registered)
 172                 list_add_tail(&entry->global_list, &async_global_pending);
 173
 174         atomic_inc(&entry_count);
 175         spin_unlock_irqrestore(&async_lock, flags);
 176
 177         /* schedule for execution */
 178         queue_work_node(node, async_wq, &entry->work);
 179
 180         return newcookie;
 181 }
 182
 183 /**
 184  * async_schedule_node_domain - NUMA specific version of async_schedule_domain
 185  * @func: function to execute asynchronously
 186  * @data: data pointer to pass to the function
 187  * @node: NUMA node that we want to schedule this on or close to
 188  * @domain: the domain
 189  *
 190  * Returns an async_cookie_t that may be used for checkpointing later.
 191  * @domain may be used in the async_synchronize_*_domain() functions to
 192  * wait within a certain synchronization domain rather than globally.
 193  *
 194  * Note: This function may be called from atomic or non-atomic contexts.
 195  *
 196  * The node requested will be honored on a best effort basis. If the node
 197  * has no CPUs associated with it then the work is distributed among all
 198  * available CPUs.
 199  */
 200 async_cookie_t async_schedule_node_domain(async_func_t func, void *data,
 201                                           int node, struct async_domain *domain)
 202 {
 203         struct async_entry *entry;
 204         unsigned long flags;
 205         async_cookie_t newcookie;
 206
 207         /* allow irq-off callers */
 208         entry = kzalloc(sizeof(struct async_entry), GFP_ATOMIC);
 209
 210         /*
 211          * If we're out of memory or if there's too much work
 212          * pending already, we execute synchronously.
 213          */
 214         if (!entry || atomic_read(&entry_count) > MAX_WORK) {
 215                 kfree(entry);
 216                 spin_lock_irqsave(&async_lock, flags);
 217                 newcookie = next_cookie++;
 218                 spin_unlock_irqrestore(&async_lock, flags);
 219
 220                 /* low on memory.. run synchronously */
 221                 func(data, newcookie);
 222                 return newcookie;
 223         }
 224
 225         return __async_schedule_node_domain(func, data, node, domain, entry);
 226 }
 227 EXPORT_SYMBOL_GPL(async_schedule_node_domain);
 228
 229 /**
 230  * async_schedule_node - NUMA specific version of async_schedule
 231  * @func: function to execute asynchronously
 232  * @data: data pointer to pass to the function
 233  * @node: NUMA node that we want to schedule this on or close to
 234  *
 235  * Returns an async_cookie_t that may be used for checkpointing later.
 236  * Note: This function may be called from atomic or non-atomic contexts.
 237  *
 238  * The node requested will be honored on a best effort basis. If the node
 239  * has no CPUs associated with it then the work is distributed among all
 240  * available CPUs.
 241  */
 242 async_cookie_t async_schedule_node(async_func_t func, void *data, int node)
 243 {
 244         return async_schedule_node_domain(func, data, node, &async_dfl_domain);
 245 }
 246 EXPORT_SYMBOL_GPL(async_schedule_node);
 247
 248 /**
 249  * async_schedule_dev_nocall - A simplified variant of async_schedule_dev()
 250  * @func: function to execute asynchronously
 251  * @dev: device argument to be passed to function
 252  *
 253  * @dev is used as both the argument for the function and to provide NUMA
 254  * context for where to run the function.
 255  *
 256  * If the asynchronous execution of @func is scheduled successfully, return
 257  * true. Otherwise, do nothing and return false, unlike async_schedule_dev()
 258  * that will run the function synchronously then.
 259  */
 260 bool async_schedule_dev_nocall(async_func_t func, struct device *dev)
 261 {
 262         struct async_entry *entry;
 263
 264         entry = kzalloc(sizeof(struct async_entry), GFP_KERNEL);
 265
 266         /* Give up if there is no memory or too much work. */
 267         if (!entry || atomic_read(&entry_count) > MAX_WORK) {
 268                 kfree(entry);
 269                 return false;
 270         }
 271
 272         __async_schedule_node_domain(func, dev, dev_to_node(dev),
 273                                      &async_dfl_domain, entry);
 274         return true;
 275 }
 276
 277 /**
 278  * async_synchronize_full - synchronize all asynchronous function calls
 279  *
 280  * This function waits until all asynchronous function calls have been done.
 281  */
 282 void async_synchronize_full(void)
 283 {
 284         async_synchronize_full_domain(NULL);
 285 }
 286 EXPORT_SYMBOL_GPL(async_synchronize_full);
 287
 288 /**
 289  * async_synchronize_full_domain - synchronize all asynchronous function within a certain domain
 290  * @domain: the domain to synchronize
 291  *
 292  * This function waits until all asynchronous function calls for the
 293  * synchronization domain specified by @domain have been done.
 294  */
 295 void async_synchronize_full_domain(struct async_domain *domain)
 296 {
 297         async_synchronize_cookie_domain(ASYNC_COOKIE_MAX, domain);
 298 }
 299 EXPORT_SYMBOL_GPL(async_synchronize_full_domain);
 300
 301 /**
 302  * async_synchronize_cookie_domain - synchronize asynchronous function calls within a certain domain with cookie checkpointing
 303  * @cookie: async_cookie_t to use as checkpoint
 304  * @domain: the domain to synchronize (%NULL for all registered domains)
 305  *
 306  * This function waits until all asynchronous function calls for the
 307  * synchronization domain specified by @domain submitted prior to @cookie
 308  * have been done.
 309  */
 310 void async_synchronize_cookie_domain(async_cookie_t cookie, struct async_domain *domain)
 311 {
 312         ktime_t starttime;
 313
 314         pr_debug("async_waiting @ %i\n", task_pid_nr(current));
 315         starttime = ktime_get();
 316
 317         wait_event(async_done, lowest_in_progress(domain) >= cookie);
 318
 319         pr_debug("async_continuing @ %i after %lli usec\n", task_pid_nr(current),
 320                  microseconds_since(starttime));
 321 }
 322 EXPORT_SYMBOL_GPL(async_synchronize_cookie_domain);
 323
 324 /**
 325  * async_synchronize_cookie - synchronize asynchronous function calls with cookie checkpointing
 326  * @cookie: async_cookie_t to use as checkpoint
 327  *
 328  * This function waits until all asynchronous function calls prior to @cookie
 329  * have been done.
 330  */
 331 void async_synchronize_cookie(async_cookie_t cookie)
 332 {
 333         async_synchronize_cookie_domain(cookie, &async_dfl_domain);
 334 }
 335 EXPORT_SYMBOL_GPL(async_synchronize_cookie);
 336
 337 /**
 338  * current_is_async - is %current an async worker task?
 339  *
 340  * Returns %true if %current is an async worker task.
 341  */
 342 bool current_is_async(void)
 343 {
 344         struct worker *worker = current_wq_worker();
 345
 346         return worker && worker->current_func == async_run_entry_fn;
 347 }
 348 EXPORT_SYMBOL_GPL(current_is_async);
 349
 350 void __init async_init(void)
 351 {
 352         /*
 353          * Async can schedule a number of interdependent work items. However,
 354          * unbound workqueues can handle only upto min_active interdependent
 355          * work items. The default min_active of 8 isn't sufficient for async
 356          * and can lead to stalls. Let's use a dedicated workqueue with raised
 357          * min_active.
 358          */
 359         async_wq = alloc_workqueue("async", WQ_UNBOUND, 0);
 360         BUG_ON(!async_wq);
 361         workqueue_set_min_active(async_wq, WQ_DFL_ACTIVE);
 362 }