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 12Goals and Theory of Operation 13 14The primary goal of this feature is to reduce the kernel boot time, 15by doing various independent hardware delays and discovery operations 16decoupled and not strictly serialized. 17 18More specifically, the asynchronous function call concept allows 19certain operations (primarily during system boot) to happen 20asynchronously, out of order, while these operations still 21have their externally visible parts happen sequentially and in-order. 22(not unlike how out-of-order CPUs retire their instructions in order) 23 24Key to the asynchronous function call implementation is the concept of 25a "sequence cookie" (which, although it has an abstracted type, can be 26thought of as a monotonically incrementing number). 27 28The async core will assign each scheduled event such a sequence cookie and 29pass this to the called functions. 30 31The asynchronously called function should before doing a globally visible 32operation, such as registering device numbers, call the 33async_synchronize_cookie() function and pass in its own cookie. The 34async_synchronize_cookie() function will make sure that all asynchronous 35operations that were scheduled prior to the operation corresponding with the 36cookie have completed. 37 38Subsystem/driver initialization code that scheduled asynchronous probe 39functions, but which shares global resources with other drivers/subsystems 40that do not use the asynchronous call feature, need to do a full 41synchronization with the async_synchronize_full() function, before returning 42from their init function. This is to maintain strict ordering between the 43asynchronous 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 59static async_cookie_t next_cookie = 1; 60 61#define MAX_WORK 32768 62#define ASYNC_COOKIE_MAX ULLONG_MAX /* infinity cookie */ 63 64static LIST_HEAD(async_global_pending); /* pending from all registered doms */ 65static ASYNC_DOMAIN(async_dfl_domain); 66static DEFINE_SPINLOCK(async_lock); 67static struct workqueue_struct *async_wq; 68 69struct 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 79static DECLARE_WAIT_QUEUE_HEAD(async_done); 80 81static atomic_t entry_count; 82 83static 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 89static 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 */ 117static 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 150static 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 */ 200async_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} 227EXPORT_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 */ 242async_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} 246EXPORT_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 */ 260bool 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 */ 282void async_synchronize_full(void) 283{ 284 async_synchronize_full_domain(NULL); 285} 286EXPORT_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 */ 295void async_synchronize_full_domain(struct async_domain *domain) 296{ 297 async_synchronize_cookie_domain(ASYNC_COOKIE_MAX, domain); 298} 299EXPORT_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 */ 310void 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} 322EXPORT_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 */ 331void async_synchronize_cookie(async_cookie_t cookie) 332{ 333 async_synchronize_cookie_domain(cookie, &async_dfl_domain); 334} 335EXPORT_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 */ 342bool current_is_async(void) 343{ 344 struct worker *worker = current_wq_worker(); 345 346 return worker && worker->current_func == async_run_entry_fn; 347} 348EXPORT_SYMBOL_GPL(current_is_async); 349 350void __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} 363