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