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 *name, *thread_name;
 169
 170     iothread->stopping = false;
 171     iothread->running = true;
 172     iothread->ctx = aio_context_new(&local_error);
 173     if (!iothread->ctx) {
 174         error_propagate(errp, local_error);
 175         return;
 176     }
 177
 178     /*
 179      * Init one GMainContext for the iothread unconditionally, even if
 180      * it's not used
 181      */
 182     iothread_init_gcontext(iothread);
 183
 184     aio_context_set_poll_params(iothread->ctx,
 185                                 iothread->poll_max_ns,
 186                                 iothread->poll_grow,
 187                                 iothread->poll_shrink,
 188                                 &local_error);
 189     if (local_error) {
 190         error_propagate(errp, local_error);
 191         aio_context_unref(iothread->ctx);
 192         iothread->ctx = NULL;
 193         return;
 194     }
 195
 196     /* This assumes we are called from a thread with useful CPU affinity for us
 197      * to inherit.
 198      */
 199     name = object_get_canonical_path_component(OBJECT(obj));
 200     thread_name = g_strdup_printf("IO %s", name);
 201     qemu_thread_create(&iothread->thread, thread_name, iothread_run,
 202                        iothread, QEMU_THREAD_JOINABLE);
 203     g_free(thread_name);
 204     g_free(name);
 205
 206     /* Wait for initialization to complete */
 207     while (iothread->thread_id == -1) {
 208         qemu_sem_wait(&iothread->init_done_sem);
 209     }
 210 }
 211
 212 typedef struct {
 213     const char *name;
 214     ptrdiff_t offset; /* field's byte offset in IOThread struct */
 215 } PollParamInfo;
 216
 217 static PollParamInfo poll_max_ns_info = {
 218     "poll-max-ns", offsetof(IOThread, poll_max_ns),
 219 };
 220 static PollParamInfo poll_grow_info = {
 221     "poll-grow", offsetof(IOThread, poll_grow),
 222 };
 223 static PollParamInfo poll_shrink_info = {
 224     "poll-shrink", offsetof(IOThread, poll_shrink),
 225 };
 226
 227 static void iothread_get_poll_param(Object *obj, Visitor *v,
 228         const char *name, void *opaque, Error **errp)
 229 {
 230     IOThread *iothread = IOTHREAD(obj);
 231     PollParamInfo *info = opaque;
 232     int64_t *field = (void *)iothread + info->offset;
 233
 234     visit_type_int64(v, name, field, errp);
 235 }
 236
 237 static void iothread_set_poll_param(Object *obj, Visitor *v,
 238         const char *name, void *opaque, Error **errp)
 239 {
 240     IOThread *iothread = IOTHREAD(obj);
 241     PollParamInfo *info = opaque;
 242     int64_t *field = (void *)iothread + info->offset;
 243     Error *local_err = NULL;
 244     int64_t value;
 245
 246     visit_type_int64(v, name, &value, &local_err);
 247     if (local_err) {
 248         goto out;
 249     }
 250
 251     if (value < 0) {
 252         error_setg(&local_err, "%s value must be in range [0, %"PRId64"]",
 253                    info->name, INT64_MAX);
 254         goto out;
 255     }
 256
 257     *field = value;
 258
 259     if (iothread->ctx) {
 260         aio_context_set_poll_params(iothread->ctx,
 261                                     iothread->poll_max_ns,
 262                                     iothread->poll_grow,
 263                                     iothread->poll_shrink,
 264                                     &local_err);
 265     }
 266
 267 out:
 268     error_propagate(errp, local_err);
 269 }
 270
 271 static void iothread_class_init(ObjectClass *klass, void *class_data)
 272 {
 273     UserCreatableClass *ucc = USER_CREATABLE_CLASS(klass);
 274     ucc->complete = iothread_complete;
 275
 276     object_class_property_add(klass, "poll-max-ns", "int",
 277                               iothread_get_poll_param,
 278                               iothread_set_poll_param,
 279                               NULL, &poll_max_ns_info, &error_abort);
 280     object_class_property_add(klass, "poll-grow", "int",
 281                               iothread_get_poll_param,
 282                               iothread_set_poll_param,
 283                               NULL, &poll_grow_info, &error_abort);
 284     object_class_property_add(klass, "poll-shrink", "int",
 285                               iothread_get_poll_param,
 286                               iothread_set_poll_param,
 287                               NULL, &poll_shrink_info, &error_abort);
 288 }
 289
 290 static const TypeInfo iothread_info = {
 291     .name = TYPE_IOTHREAD,
 292     .parent = TYPE_OBJECT,
 293     .class_init = iothread_class_init,
 294     .instance_size = sizeof(IOThread),
 295     .instance_init = iothread_instance_init,
 296     .instance_finalize = iothread_instance_finalize,
 297     .interfaces = (InterfaceInfo[]) {
 298         {TYPE_USER_CREATABLE},
 299         {}
 300     },
 301 };
 302
 303 static void iothread_register_types(void)
 304 {
 305     type_register_static(&iothread_info);
 306 }
 307
 308 type_init(iothread_register_types)
 309
 310 char *iothread_get_id(IOThread *iothread)
 311 {
 312     return object_get_canonical_path_component(OBJECT(iothread));
 313 }
 314
 315 AioContext *iothread_get_aio_context(IOThread *iothread)
 316 {
 317     return iothread->ctx;
 318 }
 319
 320 static int query_one_iothread(Object *object, void *opaque)
 321 {
 322     IOThreadInfoList ***prev = opaque;
 323     IOThreadInfoList *elem;
 324     IOThreadInfo *info;
 325     IOThread *iothread;
 326
 327     iothread = (IOThread *)object_dynamic_cast(object, TYPE_IOTHREAD);
 328     if (!iothread) {
 329         return 0;
 330     }
 331
 332     info = g_new0(IOThreadInfo, 1);
 333     info->id = iothread_get_id(iothread);
 334     info->thread_id = iothread->thread_id;
 335     info->poll_max_ns = iothread->poll_max_ns;
 336     info->poll_grow = iothread->poll_grow;
 337     info->poll_shrink = iothread->poll_shrink;
 338
 339     elem = g_new0(IOThreadInfoList, 1);
 340     elem->value = info;
 341     elem->next = NULL;
 342
 343     **prev = elem;
 344     *prev = &elem->next;
 345     return 0;
 346 }
 347
 348 IOThreadInfoList *qmp_query_iothreads(Error **errp)
 349 {
 350     IOThreadInfoList *head = NULL;
 351     IOThreadInfoList **prev = &head;
 352     Object *container = object_get_objects_root();
 353
 354     object_child_foreach(container, query_one_iothread, &prev);
 355     return head;
 356 }
 357
 358 GMainContext *iothread_get_g_main_context(IOThread *iothread)
 359 {
 360     atomic_set(&iothread->run_gcontext, 1);
 361     aio_notify(iothread->ctx);
 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 }