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         if (atomic_read(&iothread->worker_context)) {
  67             GMainLoop *loop;
  68
  69             g_main_context_push_thread_default(iothread->worker_context);
  70             iothread->main_loop =
  71                 g_main_loop_new(iothread->worker_context, TRUE);
  72             loop = iothread->main_loop;
  73
  74             g_main_loop_run(iothread->main_loop);
  75             iothread->main_loop = NULL;
  76             g_main_loop_unref(loop);
  77
  78             g_main_context_pop_thread_default(iothread->worker_context);
  79         }
  80     }
  81
  82     rcu_unregister_thread();
  83     return NULL;
  84 }
  85
  86 /* Runs in iothread_run() thread */
  87 static void iothread_stop_bh(void *opaque)
  88 {
  89     IOThread *iothread = opaque;
  90
  91     iothread->running = false; /* stop iothread_run() */
  92
  93     if (iothread->main_loop) {
  94         g_main_loop_quit(iothread->main_loop);
  95     }
  96 }
  97
  98 void iothread_stop(IOThread *iothread)
  99 {
 100     if (!iothread->ctx || iothread->stopping) {
 101         return;
 102     }
 103     iothread->stopping = true;
 104     aio_bh_schedule_oneshot(iothread->ctx, iothread_stop_bh, iothread);
 105     qemu_thread_join(&iothread->thread);
 106 }
 107
 108 static void iothread_instance_init(Object *obj)
 109 {
 110     IOThread *iothread = IOTHREAD(obj);
 111
 112     iothread->poll_max_ns = IOTHREAD_POLL_MAX_NS_DEFAULT;
 113     iothread->thread_id = -1;
 114 }
 115
 116 static void iothread_instance_finalize(Object *obj)
 117 {
 118     IOThread *iothread = IOTHREAD(obj);
 119
 120     iothread_stop(iothread);
 121
 122     if (iothread->thread_id != -1) {
 123         qemu_cond_destroy(&iothread->init_done_cond);
 124         qemu_mutex_destroy(&iothread->init_done_lock);
 125     }
 126     /*
 127      * Before glib2 2.33.10, there is a glib2 bug that GSource context
 128      * pointer may not be cleared even if the context has already been
 129      * destroyed (while it should).  Here let's free the AIO context
 130      * earlier to bypass that glib bug.
 131      *
 132      * We can remove this comment after the minimum supported glib2
 133      * version boosts to 2.33.10.  Before that, let's free the
 134      * GSources first before destroying any GMainContext.
 135      */
 136     if (iothread->ctx) {
 137         aio_context_unref(iothread->ctx);
 138         iothread->ctx = NULL;
 139     }
 140     if (iothread->worker_context) {
 141         g_main_context_unref(iothread->worker_context);
 142         iothread->worker_context = NULL;
 143     }
 144 }
 145
 146 static void iothread_complete(UserCreatable *obj, Error **errp)
 147 {
 148     Error *local_error = NULL;
 149     IOThread *iothread = IOTHREAD(obj);
 150     char *name, *thread_name;
 151
 152     iothread->stopping = false;
 153     iothread->running = true;
 154     iothread->ctx = aio_context_new(&local_error);
 155     if (!iothread->ctx) {
 156         error_propagate(errp, local_error);
 157         return;
 158     }
 159
 160     aio_context_set_poll_params(iothread->ctx,
 161                                 iothread->poll_max_ns,
 162                                 iothread->poll_grow,
 163                                 iothread->poll_shrink,
 164                                 &local_error);
 165     if (local_error) {
 166         error_propagate(errp, local_error);
 167         aio_context_unref(iothread->ctx);
 168         iothread->ctx = NULL;
 169         return;
 170     }
 171
 172     qemu_mutex_init(&iothread->init_done_lock);
 173     qemu_cond_init(&iothread->init_done_cond);
 174     iothread->once = (GOnce) G_ONCE_INIT;
 175
 176     /* This assumes we are called from a thread with useful CPU affinity for us
 177      * to inherit.
 178      */
 179     name = object_get_canonical_path_component(OBJECT(obj));
 180     thread_name = g_strdup_printf("IO %s", name);
 181     qemu_thread_create(&iothread->thread, thread_name, iothread_run,
 182                        iothread, QEMU_THREAD_JOINABLE);
 183     g_free(thread_name);
 184     g_free(name);
 185
 186     /* Wait for initialization to complete */
 187     qemu_mutex_lock(&iothread->init_done_lock);
 188     while (iothread->thread_id == -1) {
 189         qemu_cond_wait(&iothread->init_done_cond,
 190                        &iothread->init_done_lock);
 191     }
 192     qemu_mutex_unlock(&iothread->init_done_lock);
 193 }
 194
 195 typedef struct {
 196     const char *name;
 197     ptrdiff_t offset; /* field's byte offset in IOThread struct */
 198 } PollParamInfo;
 199
 200 static PollParamInfo poll_max_ns_info = {
 201     "poll-max-ns", offsetof(IOThread, poll_max_ns),
 202 };
 203 static PollParamInfo poll_grow_info = {
 204     "poll-grow", offsetof(IOThread, poll_grow),
 205 };
 206 static PollParamInfo poll_shrink_info = {
 207     "poll-shrink", offsetof(IOThread, poll_shrink),
 208 };
 209
 210 static void iothread_get_poll_param(Object *obj, Visitor *v,
 211         const char *name, void *opaque, Error **errp)
 212 {
 213     IOThread *iothread = IOTHREAD(obj);
 214     PollParamInfo *info = opaque;
 215     int64_t *field = (void *)iothread + info->offset;
 216
 217     visit_type_int64(v, name, field, errp);
 218 }
 219
 220 static void iothread_set_poll_param(Object *obj, Visitor *v,
 221         const char *name, void *opaque, Error **errp)
 222 {
 223     IOThread *iothread = IOTHREAD(obj);
 224     PollParamInfo *info = opaque;
 225     int64_t *field = (void *)iothread + info->offset;
 226     Error *local_err = NULL;
 227     int64_t value;
 228
 229     visit_type_int64(v, name, &value, &local_err);
 230     if (local_err) {
 231         goto out;
 232     }
 233
 234     if (value < 0) {
 235         error_setg(&local_err, "%s value must be in range [0, %"PRId64"]",
 236                    info->name, INT64_MAX);
 237         goto out;
 238     }
 239
 240     *field = value;
 241
 242     if (iothread->ctx) {
 243         aio_context_set_poll_params(iothread->ctx,
 244                                     iothread->poll_max_ns,
 245                                     iothread->poll_grow,
 246                                     iothread->poll_shrink,
 247                                     &local_err);
 248     }
 249
 250 out:
 251     error_propagate(errp, local_err);
 252 }
 253
 254 static void iothread_class_init(ObjectClass *klass, void *class_data)
 255 {
 256     UserCreatableClass *ucc = USER_CREATABLE_CLASS(klass);
 257     ucc->complete = iothread_complete;
 258
 259     object_class_property_add(klass, "poll-max-ns", "int",
 260                               iothread_get_poll_param,
 261                               iothread_set_poll_param,
 262                               NULL, &poll_max_ns_info, &error_abort);
 263     object_class_property_add(klass, "poll-grow", "int",
 264                               iothread_get_poll_param,
 265                               iothread_set_poll_param,
 266                               NULL, &poll_grow_info, &error_abort);
 267     object_class_property_add(klass, "poll-shrink", "int",
 268                               iothread_get_poll_param,
 269                               iothread_set_poll_param,
 270                               NULL, &poll_shrink_info, &error_abort);
 271 }
 272
 273 static const TypeInfo iothread_info = {
 274     .name = TYPE_IOTHREAD,
 275     .parent = TYPE_OBJECT,
 276     .class_init = iothread_class_init,
 277     .instance_size = sizeof(IOThread),
 278     .instance_init = iothread_instance_init,
 279     .instance_finalize = iothread_instance_finalize,
 280     .interfaces = (InterfaceInfo[]) {
 281         {TYPE_USER_CREATABLE},
 282         {}
 283     },
 284 };
 285
 286 static void iothread_register_types(void)
 287 {
 288     type_register_static(&iothread_info);
 289 }
 290
 291 type_init(iothread_register_types)
 292
 293 char *iothread_get_id(IOThread *iothread)
 294 {
 295     return object_get_canonical_path_component(OBJECT(iothread));
 296 }
 297
 298 AioContext *iothread_get_aio_context(IOThread *iothread)
 299 {
 300     return iothread->ctx;
 301 }
 302
 303 static int query_one_iothread(Object *object, void *opaque)
 304 {
 305     IOThreadInfoList ***prev = opaque;
 306     IOThreadInfoList *elem;
 307     IOThreadInfo *info;
 308     IOThread *iothread;
 309
 310     iothread = (IOThread *)object_dynamic_cast(object, TYPE_IOTHREAD);
 311     if (!iothread) {
 312         return 0;
 313     }
 314
 315     info = g_new0(IOThreadInfo, 1);
 316     info->id = iothread_get_id(iothread);
 317     info->thread_id = iothread->thread_id;
 318     info->poll_max_ns = iothread->poll_max_ns;
 319     info->poll_grow = iothread->poll_grow;
 320     info->poll_shrink = iothread->poll_shrink;
 321
 322     elem = g_new0(IOThreadInfoList, 1);
 323     elem->value = info;
 324     elem->next = NULL;
 325
 326     **prev = elem;
 327     *prev = &elem->next;
 328     return 0;
 329 }
 330
 331 IOThreadInfoList *qmp_query_iothreads(Error **errp)
 332 {
 333     IOThreadInfoList *head = NULL;
 334     IOThreadInfoList **prev = &head;
 335     Object *container = object_get_objects_root();
 336
 337     object_child_foreach(container, query_one_iothread, &prev);
 338     return head;
 339 }
 340
 341 static gpointer iothread_g_main_context_init(gpointer opaque)
 342 {
 343     AioContext *ctx;
 344     IOThread *iothread = opaque;
 345     GSource *source;
 346
 347     iothread->worker_context = g_main_context_new();
 348
 349     ctx = iothread_get_aio_context(iothread);
 350     source = aio_get_g_source(ctx);
 351     g_source_attach(source, iothread->worker_context);
 352     g_source_unref(source);
 353
 354     aio_notify(iothread->ctx);
 355     return NULL;
 356 }
 357
 358 GMainContext *iothread_get_g_main_context(IOThread *iothread)
 359 {
 360     g_once(&iothread->once, iothread_g_main_context_init, iothread);
 361
 362     return iothread->worker_context;
 363 }
 364
 365 IOThread *iothread_create(const char *id, Error **errp)
 366 {
 367     Object *obj;
 368
 369     obj = object_new_with_props(TYPE_IOTHREAD,
 370                                 object_get_internal_root(),
 371                                 id, errp, NULL);
 372
 373     return IOTHREAD(obj);
 374 }
 375
 376 void iothread_destroy(IOThread *iothread)
 377 {
 378     object_unparent(OBJECT(iothread));
 379 }
 380
 381 /* Lookup IOThread by its id.  Only finds user-created objects, not internal
 382  * iothread_create() objects. */
 383 IOThread *iothread_by_id(const char *id)
 384 {
 385     return IOTHREAD(object_resolve_path_type(id, TYPE_IOTHREAD, NULL));
 386 }