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 } 380