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