async.c

   1 /*
   2  * QEMU System Emulator
   3  *
   4  * Copyright (c) 2003-2008 Fabrice Bellard
   5  *
   6  * Permission is hereby granted, free of charge, to any person obtaining a copy
   7  * of this software and associated documentation files (the "Software"), to deal
   8  * in the Software without restriction, including without limitation the rights
   9  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  10  * copies of the Software, and to permit persons to whom the Software is
  11  * furnished to do so, subject to the following conditions:
  12  *
  13  * The above copyright notice and this permission notice shall be included in
  14  * all copies or substantial portions of the Software.
  15  *
  16  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  17  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  18  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
  19  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  20  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  21  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  22  * THE SOFTWARE.
  23  */
  24
  25 #include "qemu-common.h"
  26 #include "block/aio.h"
  27 #include "block/thread-pool.h"
  28 #include "qemu/main-loop.h"
  29 #include "qemu/atomic.h"
  30
  31 /***********************************************************/
  32 /* bottom halves (can be seen as timers which expire ASAP) */
  33
  34 struct QEMUBH {
  35     AioContext *ctx;
  36     QEMUBHFunc *cb;
  37     void *opaque;
  38     QEMUBH *next;
  39     bool scheduled;
  40     bool idle;
  41     bool deleted;
  42 };
  43
  44 QEMUBH *aio_bh_new(AioContext *ctx, QEMUBHFunc *cb, void *opaque)
  45 {
  46     QEMUBH *bh;
  47     bh = g_new(QEMUBH, 1);
  48     *bh = (QEMUBH){
  49         .ctx = ctx,
  50         .cb = cb,
  51         .opaque = opaque,
  52     };
  53     qemu_mutex_lock(&ctx->bh_lock);
  54     bh->next = ctx->first_bh;
  55     /* Make sure that the members are ready before putting bh into list */
  56     smp_wmb();
  57     ctx->first_bh = bh;
  58     qemu_mutex_unlock(&ctx->bh_lock);
  59     return bh;
  60 }
  61
  62 /* Multiple occurrences of aio_bh_poll cannot be called concurrently */
  63 int aio_bh_poll(AioContext *ctx)
  64 {
  65     QEMUBH *bh, **bhp, *next;
  66     int ret;
  67
  68     ctx->walking_bh++;
  69
  70     ret = 0;
  71     for (bh = ctx->first_bh; bh; bh = next) {
  72         /* Make sure that fetching bh happens before accessing its members */
  73         smp_read_barrier_depends();
  74         next = bh->next;
  75         /* The atomic_xchg is paired with the one in qemu_bh_schedule.  The
  76          * implicit memory barrier ensures that the callback sees all writes
  77          * done by the scheduling thread.  It also ensures that the scheduling
  78          * thread sees the zero before bh->cb has run, and thus will call
  79          * aio_notify again if necessary.
  80          */
  81         if (!bh->deleted && atomic_xchg(&bh->scheduled, 0)) {
  82             if (!bh->idle)
  83                 ret = 1;
  84             bh->idle = 0;
  85             bh->cb(bh->opaque);
  86         }
  87     }
  88
  89     ctx->walking_bh--;
  90
  91     /* remove deleted bhs */
  92     if (!ctx->walking_bh) {
  93         qemu_mutex_lock(&ctx->bh_lock);
  94         bhp = &ctx->first_bh;
  95         while (*bhp) {
  96             bh = *bhp;
  97             if (bh->deleted) {
  98                 *bhp = bh->next;
  99                 g_free(bh);
 100             } else {
 101                 bhp = &bh->next;
 102             }
 103         }
 104         qemu_mutex_unlock(&ctx->bh_lock);
 105     }
 106
 107     return ret;
 108 }
 109
 110 void qemu_bh_schedule_idle(QEMUBH *bh)
 111 {
 112     bh->idle = 1;
 113     /* Make sure that idle & any writes needed by the callback are done
 114      * before the locations are read in the aio_bh_poll.
 115      */
 116     atomic_mb_set(&bh->scheduled, 1);
 117 }
 118
 119 void qemu_bh_schedule(QEMUBH *bh)
 120 {
 121     AioContext *ctx;
 122
 123     ctx = bh->ctx;
 124     bh->idle = 0;
 125     /* The memory barrier implicit in atomic_xchg makes sure that:
 126      * 1. idle & any writes needed by the callback are done before the
 127      *    locations are read in the aio_bh_poll.
 128      * 2. ctx is loaded before scheduled is set and the callback has a chance
 129      *    to execute.
 130      */
 131     if (atomic_xchg(&bh->scheduled, 1) == 0) {
 132         aio_notify(ctx);
 133     }
 134 }
 135
 136
 137 /* This func is async.
 138  */
 139 void qemu_bh_cancel(QEMUBH *bh)
 140 {
 141     bh->scheduled = 0;
 142 }
 143
 144 /* This func is async.The bottom half will do the delete action at the finial
 145  * end.
 146  */
 147 void qemu_bh_delete(QEMUBH *bh)
 148 {
 149     bh->scheduled = 0;
 150     bh->deleted = 1;
 151 }
 152
 153 int64_t
 154 aio_compute_timeout(AioContext *ctx)
 155 {
 156     int64_t deadline;
 157     int timeout = -1;
 158     QEMUBH *bh;
 159
 160     for (bh = ctx->first_bh; bh; bh = bh->next) {
 161         if (!bh->deleted && bh->scheduled) {
 162             if (bh->idle) {
 163                 /* idle bottom halves will be polled at least
 164                  * every 10ms */
 165                 timeout = 10000000;
 166             } else {
 167                 /* non-idle bottom halves will be executed
 168                  * immediately */
 169                 return 0;
 170             }
 171         }
 172     }
 173
 174     deadline = timerlistgroup_deadline_ns(&ctx->tlg);
 175     if (deadline == 0) {
 176         return 0;
 177     } else {
 178         return qemu_soonest_timeout(timeout, deadline);
 179     }
 180 }
 181
 182 static gboolean
 183 aio_ctx_prepare(GSource *source, gint    *timeout)
 184 {
 185     AioContext *ctx = (AioContext *) source;
 186
 187     atomic_or(&ctx->notify_me, 1);
 188
 189     /* We assume there is no timeout already supplied */
 190     *timeout = qemu_timeout_ns_to_ms(aio_compute_timeout(ctx));
 191
 192     if (aio_prepare(ctx)) {
 193         *timeout = 0;
 194     }
 195
 196     return *timeout == 0;
 197 }
 198
 199 static gboolean
 200 aio_ctx_check(GSource *source)
 201 {
 202     AioContext *ctx = (AioContext *) source;
 203     QEMUBH *bh;
 204
 205     atomic_and(&ctx->notify_me, ~1);
 206     aio_notify_accept(ctx);
 207
 208     for (bh = ctx->first_bh; bh; bh = bh->next) {
 209         if (!bh->deleted && bh->scheduled) {
 210             return true;
 211         }
 212     }
 213     return aio_pending(ctx) || (timerlistgroup_deadline_ns(&ctx->tlg) == 0);
 214 }
 215
 216 static gboolean
 217 aio_ctx_dispatch(GSource     *source,
 218                  GSourceFunc  callback,
 219                  gpointer     user_data)
 220 {
 221     AioContext *ctx = (AioContext *) source;
 222
 223     assert(callback == NULL);
 224     aio_dispatch(ctx);
 225     return true;
 226 }
 227
 228 static void
 229 aio_ctx_finalize(GSource     *source)
 230 {
 231     AioContext *ctx = (AioContext *) source;
 232
 233     thread_pool_free(ctx->thread_pool);
 234     aio_set_event_notifier(ctx, &ctx->notifier, NULL);
 235     event_notifier_cleanup(&ctx->notifier);
 236     rfifolock_destroy(&ctx->lock);
 237     qemu_mutex_destroy(&ctx->bh_lock);
 238     timerlistgroup_deinit(&ctx->tlg);
 239 }
 240
 241 static GSourceFuncs aio_source_funcs = {
 242     aio_ctx_prepare,
 243     aio_ctx_check,
 244     aio_ctx_dispatch,
 245     aio_ctx_finalize
 246 };
 247
 248 GSource *aio_get_g_source(AioContext *ctx)
 249 {
 250     g_source_ref(&ctx->source);
 251     return &ctx->source;
 252 }
 253
 254 ThreadPool *aio_get_thread_pool(AioContext *ctx)
 255 {
 256     if (!ctx->thread_pool) {
 257         ctx->thread_pool = thread_pool_new(ctx);
 258     }
 259     return ctx->thread_pool;
 260 }
 261
 262 void aio_notify(AioContext *ctx)
 263 {
 264     /* Write e.g. bh->scheduled before reading ctx->notify_me.  Pairs
 265      * with atomic_or in aio_ctx_prepare or atomic_add in aio_poll.
 266      */
 267     smp_mb();
 268     if (ctx->notify_me) {
 269         event_notifier_set(&ctx->notifier);
 270         atomic_mb_set(&ctx->notified, true);
 271     }
 272 }
 273
 274 void aio_notify_accept(AioContext *ctx)
 275 {
 276     if (atomic_xchg(&ctx->notified, false)) {
 277         event_notifier_test_and_clear(&ctx->notifier);
 278     }
 279 }
 280
 281 static void aio_timerlist_notify(void *opaque)
 282 {
 283     aio_notify(opaque);
 284 }
 285
 286 static void aio_rfifolock_cb(void *opaque)
 287 {
 288     /* Kick owner thread in case they are blocked in aio_poll() */
 289     aio_notify(opaque);
 290 }
 291
 292 static void event_notifier_dummy_cb(EventNotifier *e)
 293 {
 294 }
 295
 296 AioContext *aio_context_new(Error **errp)
 297 {
 298     int ret;
 299     AioContext *ctx;
 300     ctx = (AioContext *) g_source_new(&aio_source_funcs, sizeof(AioContext));
 301     ret = event_notifier_init(&ctx->notifier, false);
 302     if (ret < 0) {
 303         g_source_destroy(&ctx->source);
 304         error_setg_errno(errp, -ret, "Failed to initialize event notifier");
 305         return NULL;
 306     }
 307     g_source_set_can_recurse(&ctx->source, true);
 308     aio_set_event_notifier(ctx, &ctx->notifier,
 309                            (EventNotifierHandler *)
 310                            event_notifier_dummy_cb);
 311     ctx->thread_pool = NULL;
 312     qemu_mutex_init(&ctx->bh_lock);
 313     rfifolock_init(&ctx->lock, aio_rfifolock_cb, ctx);
 314     timerlistgroup_init(&ctx->tlg, aio_timerlist_notify, ctx);
 315
 316     return ctx;
 317 }
 318
 319 void aio_context_ref(AioContext *ctx)
 320 {
 321     g_source_ref(&ctx->source);
 322 }
 323
 324 void aio_context_unref(AioContext *ctx)
 325 {
 326     g_source_unref(&ctx->source);
 327 }
 328
 329 void aio_context_acquire(AioContext *ctx)
 330 {
 331     rfifolock_lock(&ctx->lock);
 332 }
 333
 334 void aio_context_release(AioContext *ctx)
 335 {
 336     rfifolock_unlock(&ctx->lock);
 337 }