util/async.c

   1 /*
   2  * Data plane event loop
   3  *
   4  * Copyright (c) 2003-2008 Fabrice Bellard
   5  * Copyright (c) 2009-2017 QEMU contributors
   6  *
   7  * Permission is hereby granted, free of charge, to any person obtaining a copy
   8  * of this software and associated documentation files (the "Software"), to deal
   9  * in the Software without restriction, including without limitation the rights
  10  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  11  * copies of the Software, and to permit persons to whom the Software is
  12  * furnished to do so, subject to the following conditions:
  13  *
  14  * The above copyright notice and this permission notice shall be included in
  15  * all copies or substantial portions of the Software.
  16  *
  17  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  18  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  19  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
  20  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  21  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  22  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  23  * THE SOFTWARE.
  24  */
  25
  26 #include "qemu/osdep.h"
  27 #include "qapi/error.h"
  28 #include "qemu-common.h"
  29 #include "block/aio.h"
  30 #include "block/thread-pool.h"
  31 #include "qemu/main-loop.h"
  32 #include "qemu/atomic.h"
  33 #include "block/raw-aio.h"
  34 #include "qemu/coroutine_int.h"
  35 #include "trace.h"
  36
  37 /***********************************************************/
  38 /* bottom halves (can be seen as timers which expire ASAP) */
  39
  40 struct QEMUBH {
  41     AioContext *ctx;
  42     QEMUBHFunc *cb;
  43     void *opaque;
  44     QEMUBH *next;
  45     bool scheduled;
  46     bool idle;
  47     bool deleted;
  48 };
  49
  50 void aio_bh_schedule_oneshot(AioContext *ctx, QEMUBHFunc *cb, void *opaque)
  51 {
  52     QEMUBH *bh;
  53     bh = g_new(QEMUBH, 1);
  54     *bh = (QEMUBH){
  55         .ctx = ctx,
  56         .cb = cb,
  57         .opaque = opaque,
  58     };
  59     qemu_lockcnt_lock(&ctx->list_lock);
  60     bh->next = ctx->first_bh;
  61     bh->scheduled = 1;
  62     bh->deleted = 1;
  63     /* Make sure that the members are ready before putting bh into list */
  64     smp_wmb();
  65     ctx->first_bh = bh;
  66     qemu_lockcnt_unlock(&ctx->list_lock);
  67     aio_notify(ctx);
  68 }
  69
  70 QEMUBH *aio_bh_new(AioContext *ctx, QEMUBHFunc *cb, void *opaque)
  71 {
  72     QEMUBH *bh;
  73     bh = g_new(QEMUBH, 1);
  74     *bh = (QEMUBH){
  75         .ctx = ctx,
  76         .cb = cb,
  77         .opaque = opaque,
  78     };
  79     qemu_lockcnt_lock(&ctx->list_lock);
  80     bh->next = ctx->first_bh;
  81     /* Make sure that the members are ready before putting bh into list */
  82     smp_wmb();
  83     ctx->first_bh = bh;
  84     qemu_lockcnt_unlock(&ctx->list_lock);
  85     return bh;
  86 }
  87
  88 void aio_bh_call(QEMUBH *bh)
  89 {
  90     bh->cb(bh->opaque);
  91 }
  92
  93 /* Multiple occurrences of aio_bh_poll cannot be called concurrently.
  94  * The count in ctx->list_lock is incremented before the call, and is
  95  * not affected by the call.
  96  */
  97 int aio_bh_poll(AioContext *ctx)
  98 {
  99     QEMUBH *bh, **bhp, *next;
 100     int ret;
 101     bool deleted = false;
 102
 103     ret = 0;
 104     for (bh = atomic_rcu_read(&ctx->first_bh); bh; bh = next) {
 105         next = atomic_rcu_read(&bh->next);
 106         /* The atomic_xchg is paired with the one in qemu_bh_schedule.  The
 107          * implicit memory barrier ensures that the callback sees all writes
 108          * done by the scheduling thread.  It also ensures that the scheduling
 109          * thread sees the zero before bh->cb has run, and thus will call
 110          * aio_notify again if necessary.
 111          */
 112         if (atomic_xchg(&bh->scheduled, 0)) {
 113             /* Idle BHs don't count as progress */
 114             if (!bh->idle) {
 115                 ret = 1;
 116             }
 117             bh->idle = 0;
 118             aio_bh_call(bh);
 119         }
 120         if (bh->deleted) {
 121             deleted = true;
 122         }
 123     }
 124
 125     /* remove deleted bhs */
 126     if (!deleted) {
 127         return ret;
 128     }
 129
 130     if (qemu_lockcnt_dec_if_lock(&ctx->list_lock)) {
 131         bhp = &ctx->first_bh;
 132         while (*bhp) {
 133             bh = *bhp;
 134             if (bh->deleted && !bh->scheduled) {
 135                 *bhp = bh->next;
 136                 g_free(bh);
 137             } else {
 138                 bhp = &bh->next;
 139             }
 140         }
 141         qemu_lockcnt_inc_and_unlock(&ctx->list_lock);
 142     }
 143     return ret;
 144 }
 145
 146 void qemu_bh_schedule_idle(QEMUBH *bh)
 147 {
 148     bh->idle = 1;
 149     /* Make sure that idle & any writes needed by the callback are done
 150      * before the locations are read in the aio_bh_poll.
 151      */
 152     atomic_mb_set(&bh->scheduled, 1);
 153 }
 154
 155 void qemu_bh_schedule(QEMUBH *bh)
 156 {
 157     AioContext *ctx;
 158
 159     ctx = bh->ctx;
 160     bh->idle = 0;
 161     /* The memory barrier implicit in atomic_xchg makes sure that:
 162      * 1. idle & any writes needed by the callback are done before the
 163      *    locations are read in the aio_bh_poll.
 164      * 2. ctx is loaded before scheduled is set and the callback has a chance
 165      *    to execute.
 166      */
 167     if (atomic_xchg(&bh->scheduled, 1) == 0) {
 168         aio_notify(ctx);
 169     }
 170 }
 171
 172
 173 /* This func is async.
 174  */
 175 void qemu_bh_cancel(QEMUBH *bh)
 176 {
 177     bh->scheduled = 0;
 178 }
 179
 180 /* This func is async.The bottom half will do the delete action at the finial
 181  * end.
 182  */
 183 void qemu_bh_delete(QEMUBH *bh)
 184 {
 185     bh->scheduled = 0;
 186     bh->deleted = 1;
 187 }
 188
 189 int64_t
 190 aio_compute_timeout(AioContext *ctx)
 191 {
 192     int64_t deadline;
 193     int timeout = -1;
 194     QEMUBH *bh;
 195
 196     for (bh = atomic_rcu_read(&ctx->first_bh); bh;
 197          bh = atomic_rcu_read(&bh->next)) {
 198         if (bh->scheduled) {
 199             if (bh->idle) {
 200                 /* idle bottom halves will be polled at least
 201                  * every 10ms */
 202                 timeout = 10000000;
 203             } else {
 204                 /* non-idle bottom halves will be executed
 205                  * immediately */
 206                 return 0;
 207             }
 208         }
 209     }
 210
 211     deadline = timerlistgroup_deadline_ns(&ctx->tlg);
 212     if (deadline == 0) {
 213         return 0;
 214     } else {
 215         return qemu_soonest_timeout(timeout, deadline);
 216     }
 217 }
 218
 219 static gboolean
 220 aio_ctx_prepare(GSource *source, gint    *timeout)
 221 {
 222     AioContext *ctx = (AioContext *) source;
 223
 224     atomic_or(&ctx->notify_me, 1);
 225
 226     /* We assume there is no timeout already supplied */
 227     *timeout = qemu_timeout_ns_to_ms(aio_compute_timeout(ctx));
 228
 229     if (aio_prepare(ctx)) {
 230         *timeout = 0;
 231     }
 232
 233     return *timeout == 0;
 234 }
 235
 236 static gboolean
 237 aio_ctx_check(GSource *source)
 238 {
 239     AioContext *ctx = (AioContext *) source;
 240     QEMUBH *bh;
 241
 242     atomic_and(&ctx->notify_me, ~1);
 243     aio_notify_accept(ctx);
 244
 245     for (bh = ctx->first_bh; bh; bh = bh->next) {
 246         if (bh->scheduled) {
 247             return true;
 248         }
 249     }
 250     return aio_pending(ctx) || (timerlistgroup_deadline_ns(&ctx->tlg) == 0);
 251 }
 252
 253 static gboolean
 254 aio_ctx_dispatch(GSource     *source,
 255                  GSourceFunc  callback,
 256                  gpointer     user_data)
 257 {
 258     AioContext *ctx = (AioContext *) source;
 259
 260     assert(callback == NULL);
 261     aio_dispatch(ctx);
 262     return true;
 263 }
 264
 265 static void
 266 aio_ctx_finalize(GSource     *source)
 267 {
 268     AioContext *ctx = (AioContext *) source;
 269
 270     thread_pool_free(ctx->thread_pool);
 271
 272 #ifdef CONFIG_LINUX_AIO
 273     if (ctx->linux_aio) {
 274         laio_detach_aio_context(ctx->linux_aio, ctx);
 275         laio_cleanup(ctx->linux_aio);
 276         ctx->linux_aio = NULL;
 277     }
 278 #endif
 279
 280     assert(QSLIST_EMPTY(&ctx->scheduled_coroutines));
 281     qemu_bh_delete(ctx->co_schedule_bh);
 282
 283     qemu_lockcnt_lock(&ctx->list_lock);
 284     assert(!qemu_lockcnt_count(&ctx->list_lock));
 285     while (ctx->first_bh) {
 286         QEMUBH *next = ctx->first_bh->next;
 287
 288         /* qemu_bh_delete() must have been called on BHs in this AioContext */
 289         assert(ctx->first_bh->deleted);
 290
 291         g_free(ctx->first_bh);
 292         ctx->first_bh = next;
 293     }
 294     qemu_lockcnt_unlock(&ctx->list_lock);
 295
 296     aio_set_event_notifier(ctx, &ctx->notifier, false, NULL, NULL);
 297     event_notifier_cleanup(&ctx->notifier);
 298     qemu_rec_mutex_destroy(&ctx->lock);
 299     qemu_lockcnt_destroy(&ctx->list_lock);
 300     timerlistgroup_deinit(&ctx->tlg);
 301 }
 302
 303 static GSourceFuncs aio_source_funcs = {
 304     aio_ctx_prepare,
 305     aio_ctx_check,
 306     aio_ctx_dispatch,
 307     aio_ctx_finalize
 308 };
 309
 310 GSource *aio_get_g_source(AioContext *ctx)
 311 {
 312     g_source_ref(&ctx->source);
 313     return &ctx->source;
 314 }
 315
 316 ThreadPool *aio_get_thread_pool(AioContext *ctx)
 317 {
 318     if (!ctx->thread_pool) {
 319         ctx->thread_pool = thread_pool_new(ctx);
 320     }
 321     return ctx->thread_pool;
 322 }
 323
 324 #ifdef CONFIG_LINUX_AIO
 325 LinuxAioState *aio_get_linux_aio(AioContext *ctx)
 326 {
 327     if (!ctx->linux_aio) {
 328         ctx->linux_aio = laio_init();
 329         laio_attach_aio_context(ctx->linux_aio, ctx);
 330     }
 331     return ctx->linux_aio;
 332 }
 333 #endif
 334
 335 void aio_notify(AioContext *ctx)
 336 {
 337     /* Write e.g. bh->scheduled before reading ctx->notify_me.  Pairs
 338      * with atomic_or in aio_ctx_prepare or atomic_add in aio_poll.
 339      */
 340     smp_mb();
 341     if (ctx->notify_me) {
 342         event_notifier_set(&ctx->notifier);
 343         atomic_mb_set(&ctx->notified, true);
 344     }
 345 }
 346
 347 void aio_notify_accept(AioContext *ctx)
 348 {
 349     if (atomic_xchg(&ctx->notified, false)) {
 350         event_notifier_test_and_clear(&ctx->notifier);
 351     }
 352 }
 353
 354 static void aio_timerlist_notify(void *opaque, QEMUClockType type)
 355 {
 356     aio_notify(opaque);
 357 }
 358
 359 static void event_notifier_dummy_cb(EventNotifier *e)
 360 {
 361 }
 362
 363 /* Returns true if aio_notify() was called (e.g. a BH was scheduled) */
 364 static bool event_notifier_poll(void *opaque)
 365 {
 366     EventNotifier *e = opaque;
 367     AioContext *ctx = container_of(e, AioContext, notifier);
 368
 369     return atomic_read(&ctx->notified);
 370 }
 371
 372 static void co_schedule_bh_cb(void *opaque)
 373 {
 374     AioContext *ctx = opaque;
 375     QSLIST_HEAD(, Coroutine) straight, reversed;
 376
 377     QSLIST_MOVE_ATOMIC(&reversed, &ctx->scheduled_coroutines);
 378     QSLIST_INIT(&straight);
 379
 380     while (!QSLIST_EMPTY(&reversed)) {
 381         Coroutine *co = QSLIST_FIRST(&reversed);
 382         QSLIST_REMOVE_HEAD(&reversed, co_scheduled_next);
 383         QSLIST_INSERT_HEAD(&straight, co, co_scheduled_next);
 384     }
 385
 386     while (!QSLIST_EMPTY(&straight)) {
 387         Coroutine *co = QSLIST_FIRST(&straight);
 388         QSLIST_REMOVE_HEAD(&straight, co_scheduled_next);
 389         trace_aio_co_schedule_bh_cb(ctx, co);
 390         aio_context_acquire(ctx);
 391         qemu_coroutine_enter(co);
 392         aio_context_release(ctx);
 393     }
 394 }
 395
 396 AioContext *aio_context_new(Error **errp)
 397 {
 398     int ret;
 399     AioContext *ctx;
 400
 401     ctx = (AioContext *) g_source_new(&aio_source_funcs, sizeof(AioContext));
 402     aio_context_setup(ctx);
 403
 404     ret = event_notifier_init(&ctx->notifier, false);
 405     if (ret < 0) {
 406         error_setg_errno(errp, -ret, "Failed to initialize event notifier");
 407         goto fail;
 408     }
 409     g_source_set_can_recurse(&ctx->source, true);
 410     qemu_lockcnt_init(&ctx->list_lock);
 411
 412     ctx->co_schedule_bh = aio_bh_new(ctx, co_schedule_bh_cb, ctx);
 413     QSLIST_INIT(&ctx->scheduled_coroutines);
 414
 415     aio_set_event_notifier(ctx, &ctx->notifier,
 416                            false,
 417                            (EventNotifierHandler *)
 418                            event_notifier_dummy_cb,
 419                            event_notifier_poll);
 420 #ifdef CONFIG_LINUX_AIO
 421     ctx->linux_aio = NULL;
 422 #endif
 423     ctx->thread_pool = NULL;
 424     qemu_rec_mutex_init(&ctx->lock);
 425     timerlistgroup_init(&ctx->tlg, aio_timerlist_notify, ctx);
 426
 427     ctx->poll_ns = 0;
 428     ctx->poll_max_ns = 0;
 429     ctx->poll_grow = 0;
 430     ctx->poll_shrink = 0;
 431
 432     return ctx;
 433 fail:
 434     g_source_destroy(&ctx->source);
 435     return NULL;
 436 }
 437
 438 void aio_co_schedule(AioContext *ctx, Coroutine *co)
 439 {
 440     trace_aio_co_schedule(ctx, co);
 441     QSLIST_INSERT_HEAD_ATOMIC(&ctx->scheduled_coroutines,
 442                               co, co_scheduled_next);
 443     qemu_bh_schedule(ctx->co_schedule_bh);
 444 }
 445
 446 void aio_co_wake(struct Coroutine *co)
 447 {
 448     AioContext *ctx;
 449
 450     /* Read coroutine before co->ctx.  Matches smp_wmb in
 451      * qemu_coroutine_enter.
 452      */
 453     smp_read_barrier_depends();
 454     ctx = atomic_read(&co->ctx);
 455
 456     if (ctx != qemu_get_current_aio_context()) {
 457         aio_co_schedule(ctx, co);
 458         return;
 459     }
 460
 461     if (qemu_in_coroutine()) {
 462         Coroutine *self = qemu_coroutine_self();
 463         assert(self != co);
 464         QSIMPLEQ_INSERT_TAIL(&self->co_queue_wakeup, co, co_queue_next);
 465     } else {
 466         aio_context_acquire(ctx);
 467         qemu_coroutine_enter(co);
 468         aio_context_release(ctx);
 469     }
 470 }
 471
 472 void aio_context_ref(AioContext *ctx)
 473 {
 474     g_source_ref(&ctx->source);
 475 }
 476
 477 void aio_context_unref(AioContext *ctx)
 478 {
 479     g_source_unref(&ctx->source);
 480 }
 481
 482 void aio_context_acquire(AioContext *ctx)
 483 {
 484     qemu_rec_mutex_lock(&ctx->lock);
 485 }
 486
 487 void aio_context_release(AioContext *ctx)
 488 {
 489     qemu_rec_mutex_unlock(&ctx->lock);
 490 }