linux/kernel/async.c at master · fabgithub/linux · GitHub

Repository navigation

History

328 lines (275 loc) · 9.94 KB

Raw

100

101

102

103

104

105

106

107

108

109

110

111

112

113

114

115

116

117

118

119

120

121

122

123

124

125

126

127

128

129

130

131

132

133

134

135

136

137

138

139

140

141

142

143

144

145

146

147

148

149

150

151

152

153

154

155

156

157

158

159

160

161

162

163

164

165

166

167

168

169

170

171

172

173

174

175

176

177

178

179

180

181

182

183

184

185

186

187

188

189

190

191

192

193

194

195

196

197

198

199

200

201

202

203

204

205

206

207

208

209

210

211

212

213

214

215

216

217

218

219

220

221

222

223

224

225

226

227

228

229

230

231

232

233

234

235

236

237

238

239

240

241

242

243

244

245

246

247

248

249

250

251

252

253

254

255

256

257

258

259

260

261

262

263

264

265

266

267

268

269

270

271

272

273

274

275

276

277

278

279

280

281

282

283

284

285

286

287

288

289

290

291

292

293

294

295

296

297

298

299

300

301

302

303

304

305

306

307

308

309

310

311

312

313

314

315

316

317

318

319

320

321

322

323

324

325

326

327

328

* async.c: Asynchronous function calls for boot performance

* Author: Arjan van de Ven <arjan@linux.intel.com>

* This program is free software; you can redistribute it and/or

* modify it under the terms of the GNU General Public License

* as published by the Free Software Foundation; version 2

* of the License.

Goals and Theory of Operation

The primary goal of this feature is to reduce the kernel boot time,

by doing various independent hardware delays and discovery operations

decoupled and not strictly serialized.

More specifically, the asynchronous function call concept allows

certain operations (primarily during system boot) to happen

asynchronously, out of order, while these operations still

have their externally visible parts happen sequentially and in-order.

(not unlike how out-of-order CPUs retire their instructions in order)

Key to the asynchronous function call implementation is the concept of

a "sequence cookie" (which, although it has an abstracted type, can be

thought of as a monotonically incrementing number).

The async core will assign each scheduled event such a sequence cookie and

pass this to the called functions.

The asynchronously called function should before doing a globally visible

operation, such as registering device numbers, call the

async_synchronize_cookie() function and pass in its own cookie. The

async_synchronize_cookie() function will make sure that all asynchronous

operations that were scheduled prior to the operation corresponding with the

cookie have completed.

Subsystem/driver initialization code that scheduled asynchronous probe

functions, but which shares global resources with other drivers/subsystems

that do not use the asynchronous call feature, need to do a full

synchronization with the async_synchronize_full() function, before returning

from their init function. This is to maintain strict ordering between the

asynchronous and synchronous parts of the kernel.

#include <linux/async.h>

#include <linux/atomic.h>

#include <linux/ktime.h>

#include <linux/export.h>

#include <linux/wait.h>

#include <linux/sched.h>

#include <linux/slab.h>

#include <linux/workqueue.h>

#include "workqueue_internal.h"

static async_cookie_t next_cookie = 1;

#define MAX_WORK 32768

#define ASYNC_COOKIE_MAX ULLONG_MAX /* infinity cookie */

static LIST_HEAD(async_global_pending); /* pending from all registered doms */

static ASYNC_DOMAIN(async_dfl_domain);

static DEFINE_SPINLOCK(async_lock);

struct async_entry {

struct list_head domain_list;

struct list_head global_list;

struct work_struct work;

async_cookie_t cookie;

async_func_t func;

void *data;

struct async_domain *domain;

};

static DECLARE_WAIT_QUEUE_HEAD(async_done);

static atomic_t entry_count;

static async_cookie_t lowest_in_progress(struct async_domain *domain)

{

struct list_head *pending;

async_cookie_t ret = ASYNC_COOKIE_MAX;

unsigned long flags;

spin_lock_irqsave(&async_lock, flags);

if (domain)

pending = &domain->pending;

else

pending = &async_global_pending;

if (!list_empty(pending))

ret = list_first_entry(pending, struct async_entry,

domain_list)->cookie;

spin_unlock_irqrestore(&async_lock, flags);

return ret;

}

* pick the first pending entry and run it

static void async_run_entry_fn(struct work_struct *work)

{

struct async_entry *entry =

container_of(work, struct async_entry, work);

unsigned long flags;

ktime_t uninitialized_var(calltime), delta, rettime;

/* 1) run (and print duration) */

if (initcall_debug && system_state == SYSTEM_BOOTING) {

printk(KERN_DEBUG "calling %lli_%pF @ %i\n",

(long long)entry->cookie,

entry->func, task_pid_nr(current));

calltime = ktime_get();

}

entry->func(entry->data, entry->cookie);

if (initcall_debug && system_state == SYSTEM_BOOTING) {

rettime = ktime_get();

delta = ktime_sub(rettime, calltime);

printk(KERN_DEBUG "initcall %lli_%pF returned 0 after %lld usecs\n",

(long long)entry->cookie,

entry->func,

(long long)ktime_to_ns(delta) >> 10);

}

/* 2) remove self from the pending queues */

spin_lock_irqsave(&async_lock, flags);

list_del_init(&entry->domain_list);

list_del_init(&entry->global_list);

/* 3) free the entry */

kfree(entry);

atomic_dec(&entry_count);

spin_unlock_irqrestore(&async_lock, flags);

/* 4) wake up any waiters */

wake_up(&async_done);

}

static async_cookie_t __async_schedule(async_func_t func, void *data, struct async_domain *domain)

{

struct async_entry *entry;

unsigned long flags;

async_cookie_t newcookie;

/* allow irq-off callers */

entry = kzalloc(sizeof(struct async_entry), GFP_ATOMIC);

* If we're out of memory or if there's too much work

* pending already, we execute synchronously.

if (!entry || atomic_read(&entry_count) > MAX_WORK) {

kfree(entry);

spin_lock_irqsave(&async_lock, flags);

newcookie = next_cookie++;

spin_unlock_irqrestore(&async_lock, flags);

/* low on memory.. run synchronously */

func(data, newcookie);

return newcookie;

}

INIT_LIST_HEAD(&entry->domain_list);

INIT_LIST_HEAD(&entry->global_list);

INIT_WORK(&entry->work, async_run_entry_fn);

entry->func = func;

entry->data = data;

entry->domain = domain;

spin_lock_irqsave(&async_lock, flags);

/* allocate cookie and queue */

newcookie = entry->cookie = next_cookie++;

list_add_tail(&entry->domain_list, &domain->pending);

if (domain->registered)

list_add_tail(&entry->global_list, &async_global_pending);

atomic_inc(&entry_count);

spin_unlock_irqrestore(&async_lock, flags);

/* mark that this task has queued an async job, used by module init */

current->flags |= PF_USED_ASYNC;

/* schedule for execution */

queue_work(system_unbound_wq, &entry->work);

return newcookie;

}

/**

* async_schedule - schedule a function for asynchronous execution

* @func: function to execute asynchronously

* @data: data pointer to pass to the function

* Returns an async_cookie_t that may be used for checkpointing later.

* Note: This function may be called from atomic or non-atomic contexts.

async_cookie_t async_schedule(async_func_t func, void *data)

{

return __async_schedule(func, data, &async_dfl_domain);

}

EXPORT_SYMBOL_GPL(async_schedule);

/**

* async_schedule_domain - schedule a function for asynchronous execution within a certain domain

* @func: function to execute asynchronously

* @data: data pointer to pass to the function

* @domain: the domain

* Returns an async_cookie_t that may be used for checkpointing later.

* @domain may be used in the async_synchronize_*_domain() functions to

* wait within a certain synchronization domain rather than globally. A

* synchronization domain is specified via @domain. Note: This function

* may be called from atomic or non-atomic contexts.

async_cookie_t async_schedule_domain(async_func_t func, void *data,

struct async_domain *domain)

{

return __async_schedule(func, data, domain);

}

EXPORT_SYMBOL_GPL(async_schedule_domain);

/**

* async_synchronize_full - synchronize all asynchronous function calls

* This function waits until all asynchronous function calls have been done.

void async_synchronize_full(void)

{

async_synchronize_full_domain(NULL);

}

EXPORT_SYMBOL_GPL(async_synchronize_full);

/**

* async_unregister_domain - ensure no more anonymous waiters on this domain

* @domain: idle domain to flush out of any async_synchronize_full instances

* async_synchronize_{cookie|full}_domain() are not flushed since callers

* of these routines should know the lifetime of @domain

* Prefer ASYNC_DOMAIN_EXCLUSIVE() declarations over flushing

void async_unregister_domain(struct async_domain *domain)

{

spin_lock_irq(&async_lock);

WARN_ON(!domain->registered || !list_empty(&domain->pending));

domain->registered = 0;

spin_unlock_irq(&async_lock);

}

EXPORT_SYMBOL_GPL(async_unregister_domain);

/**

* async_synchronize_full_domain - synchronize all asynchronous function within a certain domain

* @domain: the domain to synchronize

* This function waits until all asynchronous function calls for the

* synchronization domain specified by @domain have been done.

void async_synchronize_full_domain(struct async_domain *domain)

{

async_synchronize_cookie_domain(ASYNC_COOKIE_MAX, domain);

}

EXPORT_SYMBOL_GPL(async_synchronize_full_domain);

/**

* async_synchronize_cookie_domain - synchronize asynchronous function calls within a certain domain with cookie checkpointing

* @cookie: async_cookie_t to use as checkpoint

* @domain: the domain to synchronize (%NULL for all registered domains)

* This function waits until all asynchronous function calls for the

* synchronization domain specified by @domain submitted prior to @cookie

* have been done.

void async_synchronize_cookie_domain(async_cookie_t cookie, struct async_domain *domain)

{

ktime_t uninitialized_var(starttime), delta, endtime;

if (initcall_debug && system_state == SYSTEM_BOOTING) {

printk(KERN_DEBUG "async_waiting @ %i\n", task_pid_nr(current));

starttime = ktime_get();

}

wait_event(async_done, lowest_in_progress(domain) >= cookie);

if (initcall_debug && system_state == SYSTEM_BOOTING) {

endtime = ktime_get();

delta = ktime_sub(endtime, starttime);

printk(KERN_DEBUG "async_continuing @ %i after %lli usec\n",

task_pid_nr(current),

(long long)ktime_to_ns(delta) >> 10);

}

EXPORT_SYMBOL_GPL(async_synchronize_cookie_domain);

/**

* async_synchronize_cookie - synchronize asynchronous function calls with cookie checkpointing

* @cookie: async_cookie_t to use as checkpoint

* This function waits until all asynchronous function calls prior to @cookie

* have been done.

void async_synchronize_cookie(async_cookie_t cookie)

{

async_synchronize_cookie_domain(cookie, &async_dfl_domain);

}

EXPORT_SYMBOL_GPL(async_synchronize_cookie);

/**

* current_is_async - is %current an async worker task?

* Returns %true if %current is an async worker task.

bool current_is_async(void)

{

struct worker *worker = current_wq_worker();

return worker && worker->current_func == async_run_entry_fn;

}

linux/kernel/async.c at master · fabgithub/linux · GitHub

Repository navigation

Expand file tree

Breadcrumbs

async.c

Latest commit

History

Breadcrumbs

async.c

File metadata and controls