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