iothread.c

   1 /*
   2  * Event loop thread
   3  *
   4  * Copyright Red Hat Inc., 2013
   5  *
   6  * Authors:
   7  *  Stefan Hajnoczi   <stefanha@redhat.com>
   8  *
   9  * This work is licensed under the terms of the GNU GPL, version 2 or later.
  10  * See the COPYING file in the top-level directory.
  11  *
  12  */
  13
  14 #include "qemu/osdep.h"
  15 #include "qom/object.h"
  16 #include "qom/object_interfaces.h"
  17 #include "qemu/module.h"
  18 #include "block/aio.h"
  19 #include "block/block.h"
  20 #include "sysemu/iothread.h"
  21 #include "qapi/error.h"
  22 #include "qapi/qapi-commands-misc.h"
  23 #include "qemu/error-report.h"
  24 #include "qemu/rcu.h"
  25 #include "qemu/main-loop.h"
  26
  27 typedef ObjectClass IOThreadClass;
  28
  29 #define IOTHREAD_GET_CLASS(obj) \
  30    OBJECT_GET_CLASS(IOThreadClass, obj, TYPE_IOTHREAD)
  31 #define IOTHREAD_CLASS(klass) \
  32    OBJECT_CLASS_CHECK(IOThreadClass, klass, TYPE_IOTHREAD)
  33
  34 #ifdef CONFIG_POSIX
  35 /* Benchmark results from 2016 on NVMe SSD drives show max polling times around
  36  * 16-32 microseconds yield IOPS improvements for both iodepth=1 and iodepth=32
  37  * workloads.
  38  */
  39 #define IOTHREAD_POLL_MAX_NS_DEFAULT 32768ULL
  40 #else
  41 #define IOTHREAD_POLL_MAX_NS_DEFAULT 0ULL
  42 #endif
  43
  44 static __thread IOThread *my_iothread;
  45
  46 AioContext *qemu_get_current_aio_context(void)
  47 {
  48     return my_iothread ? my_iothread->ctx : qemu_get_aio_context();
  49 }
  50
  51 static void *iothread_run(void *opaque)
  52 {
  53     IOThread *iothread = opaque;
  54
  55     rcu_register_thread();
  56
  57     my_iothread = iothread;
  58     qemu_mutex_lock(&iothread->init_done_lock);
  59     iothread->thread_id = qemu_get_thread_id();
  60     qemu_cond_signal(&iothread->init_done_cond);
  61     qemu_mutex_unlock(&iothread->init_done_lock);
  62
  63     while (iothread->running) {
  64         aio_poll(iothread->ctx, true);
  65
  66         /*
  67          * We must check the running state again in case it was
  68          * changed in previous aio_poll()
  69          */
  70         if (iothread->running && atomic_read(&iothread->worker_context)) {
  71             GMainLoop *loop;
  72
  73             g_main_context_push_thread_default(iothread->worker_context);
  74             iothread->main_loop =
  75                 g_main_loop_new(iothread->worker_context, TRUE);
  76             loop = iothread->main_loop;
  77
  78             g_main_loop_run(iothread->main_loop);
  79             iothread->main_loop = NULL;
  80             g_main_loop_unref(loop);
  81
  82             g_main_context_pop_thread_default(iothread->worker_context);
  83         }
  84     }
  85
  86     rcu_unregister_thread();
  87     return NULL;
  88 }
  89
  90 /* Runs in iothread_run() thread */
  91 static void iothread_stop_bh(void *opaque)
  92 {
  93     IOThread *iothread = opaque;
  94
  95     iothread->running = false; /* stop iothread_run() */
  96
  97     if (iothread->main_loop) {
  98         g_main_loop_quit(iothread->main_loop);
  99     }
 100 }
 101
 102 void iothread_stop(IOThread *iothread)
 103 {
 104     if (!iothread->ctx || iothread->stopping) {
 105         return;
 106     }
 107     iothread->stopping = true;
 108     aio_bh_schedule_oneshot(iothread->ctx, iothread_stop_bh, iothread);
 109     qemu_thread_join(&iothread->thread);
 110 }
 111
 112 static void iothread_instance_init(Object *obj)
 113 {
 114     IOThread *iothread = IOTHREAD(obj);
 115
 116     iothread->poll_max_ns = IOTHREAD_POLL_MAX_NS_DEFAULT;
 117     iothread->thread_id = -1;
 118 }
 119
 120 static void iothread_instance_finalize(Object *obj)
 121 {
 122     IOThread *iothread = IOTHREAD(obj);
 123
 124     iothread_stop(iothread);
 125
 126     if (iothread->thread_id != -1) {
 127         qemu_cond_destroy(&iothread->init_done_cond);
 128         qemu_mutex_destroy(&iothread->init_done_lock);
 129     }
 130     /*
 131      * Before glib2 2.33.10, there is a glib2 bug that GSource context
 132      * pointer may not be cleared even if the context has already been
 133      * destroyed (while it should).  Here let's free the AIO context
 134      * earlier to bypass that glib bug.
 135      *
 136      * We can remove this comment after the minimum supported glib2
 137      * version boosts to 2.33.10.  Before that, let's free the
 138      * GSources first before destroying any GMainContext.
 139      */
 140     if (iothread->ctx) {
 141         aio_context_unref(iothread->ctx);
 142         iothread->ctx = NULL;
 143     }
 144     if (iothread->worker_context) {
 145         g_main_context_unref(iothread->worker_context);
 146         iothread->worker_context = NULL;
 147     }
 148 }
 149
 150 static void iothread_complete(UserCreatable *obj, Error **errp)
 151 {
 152     Error *local_error = NULL;
 153     IOThread *iothread = IOTHREAD(obj);
 154     char *name, *thread_name;
 155
 156     iothread->stopping = false;
 157     iothread->running = true;
 158     iothread->ctx = aio_context_new(&local_error);
 159     if (!iothread->ctx) {
 160         error_propagate(errp, local_error);
 161         return;
 162     }
 163
 164     aio_context_set_poll_params(iothread->ctx,
 165                                 iothread->poll_max_ns,
 166                                 iothread->poll_grow,
 167                                 iothread->poll_shrink,
 168                                 &local_error);
 169     if (local_error) {
 170         error_propagate(errp, local_error);
 171         aio_context_unref(iothread->ctx);
 172         iothread->ctx = NULL;
 173         return;
 174     }
 175
 176     qemu_mutex_init(&iothread->init_done_lock);
 177     qemu_cond_init(&iothread->init_done_cond);
 178     iothread->once = (GOnce) G_ONCE_INIT;
 179
 180     /* This assumes we are called from a thread with useful CPU affinity for us
 181      * to inherit.
 182      */
 183     name = object_get_canonical_path_component(OBJECT(obj));
 184     thread_name = g_strdup_printf("IO %s", name);
 185     qemu_thread_create(&iothread->thread, thread_name, iothread_run,
 186                        iothread, QEMU_THREAD_JOINABLE);
 187     g_free(thread_name);
 188     g_free(name);
 189
 190     /* Wait for initialization to complete */
 191     qemu_mutex_lock(&iothread->init_done_lock);
 192     while (iothread->thread_id == -1) {
 193         qemu_cond_wait(&iothread->init_done_cond,
 194                        &iothread->init_done_lock);
 195     }
 196     qemu_mutex_unlock(&iothread->init_done_lock);
 197 }
 198
 199 typedef struct {
 200     const char *name;
 201     ptrdiff_t offset; /* field's byte offset in IOThread struct */
 202 } PollParamInfo;
 203
 204 static PollParamInfo poll_max_ns_info = {
 205     "poll-max-ns", offsetof(IOThread, poll_max_ns),
 206 };
 207 static PollParamInfo poll_grow_info = {
 208     "poll-grow", offsetof(IOThread, poll_grow),
 209 };
 210 static PollParamInfo poll_shrink_info = {
 211     "poll-shrink", offsetof(IOThread, poll_shrink),
 212 };
 213
 214 static void iothread_get_poll_param(Object *obj, Visitor *v,
 215         const char *name, void *opaque, Error **errp)
 216 {
 217     IOThread *iothread = IOTHREAD(obj);
 218     PollParamInfo *info = opaque;
 219     int64_t *field = (void *)iothread + info->offset;
 220
 221     visit_type_int64(v, name, field, errp);
 222 }
 223
 224 static void iothread_set_poll_param(Object *obj, Visitor *v,
 225         const char *name, void *opaque, Error **errp)
 226 {
 227     IOThread *iothread = IOTHREAD(obj);
 228     PollParamInfo *info = opaque;
 229     int64_t *field = (void *)iothread + info->offset;
 230     Error *local_err = NULL;
 231     int64_t value;
 232
 233     visit_type_int64(v, name, &value, &local_err);
 234     if (local_err) {
 235         goto out;
 236     }
 237
 238     if (value < 0) {
 239         error_setg(&local_err, "%s value must be in range [0, %"PRId64"]",
 240                    info->name, INT64_MAX);
 241         goto out;
 242     }
 243
 244     *field = value;
 245
 246     if (iothread->ctx) {
 247         aio_context_set_poll_params(iothread->ctx,
 248                                     iothread->poll_max_ns,
 249                                     iothread->poll_grow,
 250                                     iothread->poll_shrink,
 251                                     &local_err);
 252     }
 253
 254 out:
 255     error_propagate(errp, local_err);
 256 }
 257
 258 static void iothread_class_init(ObjectClass *klass, void *class_data)
 259 {
 260     UserCreatableClass *ucc = USER_CREATABLE_CLASS(klass);
 261     ucc->complete = iothread_complete;
 262
 263     object_class_property_add(klass, "poll-max-ns", "int",
 264                               iothread_get_poll_param,
 265                               iothread_set_poll_param,
 266                               NULL, &poll_max_ns_info, &error_abort);
 267     object_class_property_add(klass, "poll-grow", "int",
 268                               iothread_get_poll_param,
 269                               iothread_set_poll_param,
 270                               NULL, &poll_grow_info, &error_abort);
 271     object_class_property_add(klass, "poll-shrink", "int",
 272                               iothread_get_poll_param,
 273                               iothread_set_poll_param,
 274                               NULL, &poll_shrink_info, &error_abort);
 275 }
 276
 277 static const TypeInfo iothread_info = {
 278     .name = TYPE_IOTHREAD,
 279     .parent = TYPE_OBJECT,
 280     .class_init = iothread_class_init,
 281     .instance_size = sizeof(IOThread),
 282     .instance_init = iothread_instance_init,
 283     .instance_finalize = iothread_instance_finalize,
 284     .interfaces = (InterfaceInfo[]) {
 285         {TYPE_USER_CREATABLE},
 286         {}
 287     },
 288 };
 289
 290 static void iothread_register_types(void)
 291 {
 292     type_register_static(&iothread_info);
 293 }
 294
 295 type_init(iothread_register_types)
 296
 297 char *iothread_get_id(IOThread *iothread)
 298 {
 299     return object_get_canonical_path_component(OBJECT(iothread));
 300 }
 301
 302 AioContext *iothread_get_aio_context(IOThread *iothread)
 303 {
 304     return iothread->ctx;
 305 }
 306
 307 static int query_one_iothread(Object *object, void *opaque)
 308 {
 309     IOThreadInfoList ***prev = opaque;
 310     IOThreadInfoList *elem;
 311     IOThreadInfo *info;
 312     IOThread *iothread;
 313
 314     iothread = (IOThread *)object_dynamic_cast(object, TYPE_IOTHREAD);
 315     if (!iothread) {
 316         return 0;
 317     }
 318
 319     info = g_new0(IOThreadInfo, 1);
 320     info->id = iothread_get_id(iothread);
 321     info->thread_id = iothread->thread_id;
 322     info->poll_max_ns = iothread->poll_max_ns;
 323     info->poll_grow = iothread->poll_grow;
 324     info->poll_shrink = iothread->poll_shrink;
 325
 326     elem = g_new0(IOThreadInfoList, 1);
 327     elem->value = info;
 328     elem->next = NULL;
 329
 330     **prev = elem;
 331     *prev = &elem->next;
 332     return 0;
 333 }
 334
 335 IOThreadInfoList *qmp_query_iothreads(Error **errp)
 336 {
 337     IOThreadInfoList *head = NULL;
 338     IOThreadInfoList **prev = &head;
 339     Object *container = object_get_objects_root();
 340
 341     object_child_foreach(container, query_one_iothread, &prev);
 342     return head;
 343 }
 344
 345 static gpointer iothread_g_main_context_init(gpointer opaque)
 346 {
 347     AioContext *ctx;
 348     IOThread *iothread = opaque;
 349     GSource *source;
 350
 351     iothread->worker_context = g_main_context_new();
 352
 353     ctx = iothread_get_aio_context(iothread);
 354     source = aio_get_g_source(ctx);
 355     g_source_attach(source, iothread->worker_context);
 356     g_source_unref(source);
 357
 358     aio_notify(iothread->ctx);
 359     return NULL;
 360 }
 361
 362 GMainContext *iothread_get_g_main_context(IOThread *iothread)
 363 {
 364     g_once(&iothread->once, iothread_g_main_context_init, iothread);
 365
 366     return iothread->worker_context;
 367 }
 368
 369 IOThread *iothread_create(const char *id, Error **errp)
 370 {
 371     Object *obj;
 372
 373     obj = object_new_with_props(TYPE_IOTHREAD,
 374                                 object_get_internal_root(),
 375                                 id, errp, NULL);
 376
 377     return IOTHREAD(obj);
 378 }
 379
 380 void iothread_destroy(IOThread *iothread)
 381 {
 382     object_unparent(OBJECT(iothread));
 383 }
 384
 385 /* Lookup IOThread by its id.  Only finds user-created objects, not internal
 386  * iothread_create() objects. */
 387 IOThread *iothread_by_id(const char *id)
 388 {
 389     return IOTHREAD(object_resolve_path_type(id, TYPE_IOTHREAD, NULL));
 390 }