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     iothread->thread_id = qemu_get_thread_id();
  59     qemu_sem_post(&iothread->init_done_sem);
  60
  61     while (iothread->running) {
  62         aio_poll(iothread->ctx, true);
  63
  64         /*
  65          * We must check the running state again in case it was
  66          * changed in previous aio_poll()
  67          */
  68         if (iothread->running && atomic_read(&iothread->run_gcontext)) {
  69             GMainLoop *loop;
  70
  71             g_main_context_push_thread_default(iothread->worker_context);
  72             iothread->main_loop =
  73                 g_main_loop_new(iothread->worker_context, TRUE);
  74             loop = iothread->main_loop;
  75
  76             g_main_loop_run(iothread->main_loop);
  77             iothread->main_loop = NULL;
  78             g_main_loop_unref(loop);
  79
  80             g_main_context_pop_thread_default(iothread->worker_context);
  81         }
  82     }
  83
  84     rcu_unregister_thread();
  85     return NULL;
  86 }
  87
  88 /* Runs in iothread_run() thread */
  89 static void iothread_stop_bh(void *opaque)
  90 {
  91     IOThread *iothread = opaque;
  92
  93     iothread->running = false; /* stop iothread_run() */
  94
  95     if (iothread->main_loop) {
  96         g_main_loop_quit(iothread->main_loop);
  97     }
  98 }
  99
 100 void iothread_stop(IOThread *iothread)
 101 {
 102     if (!iothread->ctx || iothread->stopping) {
 103         return;
 104     }
 105     iothread->stopping = true;
 106     aio_bh_schedule_oneshot(iothread->ctx, iothread_stop_bh, iothread);
 107     qemu_thread_join(&iothread->thread);
 108 }
 109
 110 static void iothread_instance_init(Object *obj)
 111 {
 112     IOThread *iothread = IOTHREAD(obj);
 113
 114     iothread->poll_max_ns = IOTHREAD_POLL_MAX_NS_DEFAULT;
 115     iothread->thread_id = -1;
 116     qemu_sem_init(&iothread->init_done_sem, 0);
 117     /* By default, we don't run gcontext */
 118     atomic_set(&iothread->run_gcontext, 0);
 119 }
 120
 121 static void iothread_instance_finalize(Object *obj)
 122 {
 123     IOThread *iothread = IOTHREAD(obj);
 124
 125     iothread_stop(iothread);
 126
 127     /*
 128      * Before glib2 2.33.10, there is a glib2 bug that GSource context
 129      * pointer may not be cleared even if the context has already been
 130      * destroyed (while it should).  Here let's free the AIO context
 131      * earlier to bypass that glib bug.
 132      *
 133      * We can remove this comment after the minimum supported glib2
 134      * version boosts to 2.33.10.  Before that, let's free the
 135      * GSources first before destroying any GMainContext.
 136      */
 137     if (iothread->ctx) {
 138         aio_context_unref(iothread->ctx);
 139         iothread->ctx = NULL;
 140     }
 141     if (iothread->worker_context) {
 142         g_main_context_unref(iothread->worker_context);
 143         iothread->worker_context = NULL;
 144     }
 145     qemu_sem_destroy(&iothread->init_done_sem);
 146 }
 147
 148 static void iothread_init_gcontext(IOThread *iothread)
 149 {
 150     GSource *source;
 151
 152     iothread->worker_context = g_main_context_new();
 153     source = aio_get_g_source(iothread_get_aio_context(iothread));
 154     g_source_attach(source, iothread->worker_context);
 155     g_source_unref(source);
 156 }
 157
 158 static void iothread_complete(UserCreatable *obj, Error **errp)
 159 {
 160     Error *local_error = NULL;
 161     IOThread *iothread = IOTHREAD(obj);
 162     char *name, *thread_name;
 163
 164     iothread->stopping = false;
 165     iothread->running = true;
 166     iothread->ctx = aio_context_new(&local_error);
 167     if (!iothread->ctx) {
 168         error_propagate(errp, local_error);
 169         return;
 170     }
 171
 172     /*
 173      * Init one GMainContext for the iothread unconditionally, even if
 174      * it's not used
 175      */
 176     iothread_init_gcontext(iothread);
 177
 178     aio_context_set_poll_params(iothread->ctx,
 179                                 iothread->poll_max_ns,
 180                                 iothread->poll_grow,
 181                                 iothread->poll_shrink,
 182                                 &local_error);
 183     if (local_error) {
 184         error_propagate(errp, local_error);
 185         aio_context_unref(iothread->ctx);
 186         iothread->ctx = NULL;
 187         return;
 188     }
 189
 190     /* This assumes we are called from a thread with useful CPU affinity for us
 191      * to inherit.
 192      */
 193     name = object_get_canonical_path_component(OBJECT(obj));
 194     thread_name = g_strdup_printf("IO %s", name);
 195     qemu_thread_create(&iothread->thread, thread_name, iothread_run,
 196                        iothread, QEMU_THREAD_JOINABLE);
 197     g_free(thread_name);
 198     g_free(name);
 199
 200     /* Wait for initialization to complete */
 201     while (iothread->thread_id == -1) {
 202         qemu_sem_wait(&iothread->init_done_sem);
 203     }
 204 }
 205
 206 typedef struct {
 207     const char *name;
 208     ptrdiff_t offset; /* field's byte offset in IOThread struct */
 209 } PollParamInfo;
 210
 211 static PollParamInfo poll_max_ns_info = {
 212     "poll-max-ns", offsetof(IOThread, poll_max_ns),
 213 };
 214 static PollParamInfo poll_grow_info = {
 215     "poll-grow", offsetof(IOThread, poll_grow),
 216 };
 217 static PollParamInfo poll_shrink_info = {
 218     "poll-shrink", offsetof(IOThread, poll_shrink),
 219 };
 220
 221 static void iothread_get_poll_param(Object *obj, Visitor *v,
 222         const char *name, void *opaque, Error **errp)
 223 {
 224     IOThread *iothread = IOTHREAD(obj);
 225     PollParamInfo *info = opaque;
 226     int64_t *field = (void *)iothread + info->offset;
 227
 228     visit_type_int64(v, name, field, errp);
 229 }
 230
 231 static void iothread_set_poll_param(Object *obj, Visitor *v,
 232         const char *name, void *opaque, Error **errp)
 233 {
 234     IOThread *iothread = IOTHREAD(obj);
 235     PollParamInfo *info = opaque;
 236     int64_t *field = (void *)iothread + info->offset;
 237     Error *local_err = NULL;
 238     int64_t value;
 239
 240     visit_type_int64(v, name, &value, &local_err);
 241     if (local_err) {
 242         goto out;
 243     }
 244
 245     if (value < 0) {
 246         error_setg(&local_err, "%s value must be in range [0, %"PRId64"]",
 247                    info->name, INT64_MAX);
 248         goto out;
 249     }
 250
 251     *field = value;
 252
 253     if (iothread->ctx) {
 254         aio_context_set_poll_params(iothread->ctx,
 255                                     iothread->poll_max_ns,
 256                                     iothread->poll_grow,
 257                                     iothread->poll_shrink,
 258                                     &local_err);
 259     }
 260
 261 out:
 262     error_propagate(errp, local_err);
 263 }
 264
 265 static void iothread_class_init(ObjectClass *klass, void *class_data)
 266 {
 267     UserCreatableClass *ucc = USER_CREATABLE_CLASS(klass);
 268     ucc->complete = iothread_complete;
 269
 270     object_class_property_add(klass, "poll-max-ns", "int",
 271                               iothread_get_poll_param,
 272                               iothread_set_poll_param,
 273                               NULL, &poll_max_ns_info, &error_abort);
 274     object_class_property_add(klass, "poll-grow", "int",
 275                               iothread_get_poll_param,
 276                               iothread_set_poll_param,
 277                               NULL, &poll_grow_info, &error_abort);
 278     object_class_property_add(klass, "poll-shrink", "int",
 279                               iothread_get_poll_param,
 280                               iothread_set_poll_param,
 281                               NULL, &poll_shrink_info, &error_abort);
 282 }
 283
 284 static const TypeInfo iothread_info = {
 285     .name = TYPE_IOTHREAD,
 286     .parent = TYPE_OBJECT,
 287     .class_init = iothread_class_init,
 288     .instance_size = sizeof(IOThread),
 289     .instance_init = iothread_instance_init,
 290     .instance_finalize = iothread_instance_finalize,
 291     .interfaces = (InterfaceInfo[]) {
 292         {TYPE_USER_CREATABLE},
 293         {}
 294     },
 295 };
 296
 297 static void iothread_register_types(void)
 298 {
 299     type_register_static(&iothread_info);
 300 }
 301
 302 type_init(iothread_register_types)
 303
 304 char *iothread_get_id(IOThread *iothread)
 305 {
 306     return object_get_canonical_path_component(OBJECT(iothread));
 307 }
 308
 309 AioContext *iothread_get_aio_context(IOThread *iothread)
 310 {
 311     return iothread->ctx;
 312 }
 313
 314 static int query_one_iothread(Object *object, void *opaque)
 315 {
 316     IOThreadInfoList ***prev = opaque;
 317     IOThreadInfoList *elem;
 318     IOThreadInfo *info;
 319     IOThread *iothread;
 320
 321     iothread = (IOThread *)object_dynamic_cast(object, TYPE_IOTHREAD);
 322     if (!iothread) {
 323         return 0;
 324     }
 325
 326     info = g_new0(IOThreadInfo, 1);
 327     info->id = iothread_get_id(iothread);
 328     info->thread_id = iothread->thread_id;
 329     info->poll_max_ns = iothread->poll_max_ns;
 330     info->poll_grow = iothread->poll_grow;
 331     info->poll_shrink = iothread->poll_shrink;
 332
 333     elem = g_new0(IOThreadInfoList, 1);
 334     elem->value = info;
 335     elem->next = NULL;
 336
 337     **prev = elem;
 338     *prev = &elem->next;
 339     return 0;
 340 }
 341
 342 IOThreadInfoList *qmp_query_iothreads(Error **errp)
 343 {
 344     IOThreadInfoList *head = NULL;
 345     IOThreadInfoList **prev = &head;
 346     Object *container = object_get_objects_root();
 347
 348     object_child_foreach(container, query_one_iothread, &prev);
 349     return head;
 350 }
 351
 352 GMainContext *iothread_get_g_main_context(IOThread *iothread)
 353 {
 354     atomic_set(&iothread->run_gcontext, 1);
 355     aio_notify(iothread->ctx);
 356     return iothread->worker_context;
 357 }
 358
 359 IOThread *iothread_create(const char *id, Error **errp)
 360 {
 361     Object *obj;
 362
 363     obj = object_new_with_props(TYPE_IOTHREAD,
 364                                 object_get_internal_root(),
 365                                 id, errp, NULL);
 366
 367     return IOTHREAD(obj);
 368 }
 369
 370 void iothread_destroy(IOThread *iothread)
 371 {
 372     object_unparent(OBJECT(iothread));
 373 }
 374
 375 /* Lookup IOThread by its id.  Only finds user-created objects, not internal
 376  * iothread_create() objects. */
 377 IOThread *iothread_by_id(const char *id)
 378 {
 379     return IOTHREAD(object_resolve_path_type(id, TYPE_IOTHREAD, NULL));
 380 }