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_malloc0(sizeof(QEMUBH));
  48     bh->ctx = ctx;
  49     bh->cb = cb;
  50     bh->opaque = opaque;
  51     qemu_mutex_lock(&ctx->bh_lock);
  52     bh->next = ctx->first_bh;
  53     /* Make sure that the members are ready before putting bh into list */
  54     smp_wmb();
  55     ctx->first_bh = bh;
  56     qemu_mutex_unlock(&ctx->bh_lock);
  57     return bh;
  58 }
  59
  60 /* Multiple occurrences of aio_bh_poll cannot be called concurrently */
  61 int aio_bh_poll(AioContext *ctx)
  62 {
  63     QEMUBH *bh, **bhp, *next;
  64     int ret;
  65
  66     ctx->walking_bh++;
  67
  68     ret = 0;
  69     for (bh = ctx->first_bh; bh; bh = next) {
  70         /* Make sure that fetching bh happens before accessing its members */
  71         smp_read_barrier_depends();
  72         next = bh->next;
  73         if (!bh->deleted && bh->scheduled) {
  74             bh->scheduled = 0;
  75             /* Paired with write barrier in bh schedule to ensure reading for
  76              * idle & callbacks coming after bh's scheduling.
  77              */
  78             smp_rmb();
  79             if (!bh->idle)
  80                 ret = 1;
  81             bh->idle = 0;
  82             bh->cb(bh->opaque);
  83         }
  84     }
  85
  86     ctx->walking_bh--;
  87
  88     /* remove deleted bhs */
  89     if (!ctx->walking_bh) {
  90         qemu_mutex_lock(&ctx->bh_lock);
  91         bhp = &ctx->first_bh;
  92         while (*bhp) {
  93             bh = *bhp;
  94             if (bh->deleted) {
  95                 *bhp = bh->next;
  96                 g_free(bh);
  97             } else {
  98                 bhp = &bh->next;
  99             }
 100         }
 101         qemu_mutex_unlock(&ctx->bh_lock);
 102     }
 103
 104     return ret;
 105 }
 106
 107 void qemu_bh_schedule_idle(QEMUBH *bh)
 108 {
 109     if (bh->scheduled)
 110         return;
 111     bh->idle = 1;
 112     /* Make sure that idle & any writes needed by the callback are done
 113      * before the locations are read in the aio_bh_poll.
 114      */
 115     smp_wmb();
 116     bh->scheduled = 1;
 117 }
 118
 119 void qemu_bh_schedule(QEMUBH *bh)
 120 {
 121     AioContext *ctx;
 122
 123     if (bh->scheduled)
 124         return;
 125     ctx = bh->ctx;
 126     bh->idle = 0;
 127     /* Make sure that:
 128      * 1. idle & any writes needed by the callback are done before the
 129      *    locations are read in the aio_bh_poll.
 130      * 2. ctx is loaded before scheduled is set and the callback has a chance
 131      *    to execute.
 132      */
 133     smp_mb();
 134     bh->scheduled = 1;
 135     aio_notify(ctx);
 136 }
 137
 138
 139 /* This func is async.
 140  */
 141 void qemu_bh_cancel(QEMUBH *bh)
 142 {
 143     bh->scheduled = 0;
 144 }
 145
 146 /* This func is async.The bottom half will do the delete action at the finial
 147  * end.
 148  */
 149 void qemu_bh_delete(QEMUBH *bh)
 150 {
 151     bh->scheduled = 0;
 152     bh->deleted = 1;
 153 }
 154
 155 int64_t
 156 aio_compute_timeout(AioContext *ctx)
 157 {
 158     int64_t deadline;
 159     int timeout = -1;
 160     QEMUBH *bh;
 161
 162     for (bh = ctx->first_bh; bh; bh = bh->next) {
 163         if (!bh->deleted && bh->scheduled) {
 164             if (bh->idle) {
 165                 /* idle bottom halves will be polled at least
 166                  * every 10ms */
 167                 timeout = 10000000;
 168             } else {
 169                 /* non-idle bottom halves will be executed
 170                  * immediately */
 171                 return 0;
 172             }
 173         }
 174     }
 175
 176     deadline = timerlistgroup_deadline_ns(&ctx->tlg);
 177     if (deadline == 0) {
 178         return 0;
 179     } else {
 180         return qemu_soonest_timeout(timeout, deadline);
 181     }
 182 }
 183
 184 static gboolean
 185 aio_ctx_prepare(GSource *source, gint    *timeout)
 186 {
 187     AioContext *ctx = (AioContext *) source;
 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     for (bh = ctx->first_bh; bh; bh = bh->next) {
 206         if (!bh->deleted && bh->scheduled) {
 207             return true;
 208         }
 209     }
 210     return aio_pending(ctx) || (timerlistgroup_deadline_ns(&ctx->tlg) == 0);
 211 }
 212
 213 static gboolean
 214 aio_ctx_dispatch(GSource     *source,
 215                  GSourceFunc  callback,
 216                  gpointer     user_data)
 217 {
 218     AioContext *ctx = (AioContext *) source;
 219
 220     assert(callback == NULL);
 221     aio_dispatch(ctx);
 222     return true;
 223 }
 224
 225 static void
 226 aio_ctx_finalize(GSource     *source)
 227 {
 228     AioContext *ctx = (AioContext *) source;
 229
 230     thread_pool_free(ctx->thread_pool);
 231     aio_set_event_notifier(ctx, &ctx->notifier, NULL);
 232     event_notifier_cleanup(&ctx->notifier);
 233     rfifolock_destroy(&ctx->lock);
 234     qemu_mutex_destroy(&ctx->bh_lock);
 235     g_array_free(ctx->pollfds, TRUE);
 236     timerlistgroup_deinit(&ctx->tlg);
 237 }
 238
 239 static GSourceFuncs aio_source_funcs = {
 240     aio_ctx_prepare,
 241     aio_ctx_check,
 242     aio_ctx_dispatch,
 243     aio_ctx_finalize
 244 };
 245
 246 GSource *aio_get_g_source(AioContext *ctx)
 247 {
 248     g_source_ref(&ctx->source);
 249     return &ctx->source;
 250 }
 251
 252 ThreadPool *aio_get_thread_pool(AioContext *ctx)
 253 {
 254     if (!ctx->thread_pool) {
 255         ctx->thread_pool = thread_pool_new(ctx);
 256     }
 257     return ctx->thread_pool;
 258 }
 259
 260 void aio_set_dispatching(AioContext *ctx, bool dispatching)
 261 {
 262     ctx->dispatching = dispatching;
 263     if (!dispatching) {
 264         /* Write ctx->dispatching before reading e.g. bh->scheduled.
 265          * Optimization: this is only needed when we're entering the "unsafe"
 266          * phase where other threads must call event_notifier_set.
 267          */
 268         smp_mb();
 269     }
 270 }
 271
 272 void aio_notify(AioContext *ctx)
 273 {
 274     /* Write e.g. bh->scheduled before reading ctx->dispatching.  */
 275     smp_mb();
 276     if (!ctx->dispatching) {
 277         event_notifier_set(&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 AioContext *aio_context_new(Error **errp)
 293 {
 294     int ret;
 295     AioContext *ctx;
 296     ctx = (AioContext *) g_source_new(&aio_source_funcs, sizeof(AioContext));
 297     ret = event_notifier_init(&ctx->notifier, false);
 298     if (ret < 0) {
 299         g_source_destroy(&ctx->source);
 300         error_setg_errno(errp, -ret, "Failed to initialize event notifier");
 301         return NULL;
 302     }
 303     aio_set_event_notifier(ctx, &ctx->notifier,
 304                            (EventNotifierHandler *)
 305                            event_notifier_test_and_clear);
 306     ctx->pollfds = g_array_new(FALSE, FALSE, sizeof(GPollFD));
 307     ctx->thread_pool = NULL;
 308     qemu_mutex_init(&ctx->bh_lock);
 309     rfifolock_init(&ctx->lock, aio_rfifolock_cb, ctx);
 310     timerlistgroup_init(&ctx->tlg, aio_timerlist_notify, ctx);
 311
 312     return ctx;
 313 }
 314
 315 void aio_context_ref(AioContext *ctx)
 316 {
 317     g_source_ref(&ctx->source);
 318 }
 319
 320 void aio_context_unref(AioContext *ctx)
 321 {
 322     g_source_unref(&ctx->source);
 323 }
 324
 325 void aio_context_acquire(AioContext *ctx)
 326 {
 327     rfifolock_lock(&ctx->lock);
 328 }
 329
 330 void aio_context_release(AioContext *ctx)
 331 {
 332     rfifolock_unlock(&ctx->lock);
 333 }