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 DECLARE_CLASS_CHECKERS(IOThreadClass, IOTHREAD, 30 TYPE_IOTHREAD) 31 32 #ifdef CONFIG_POSIX 33 /* Benchmark results from 2016 on NVMe SSD drives show max polling times around 34 * 16-32 microseconds yield IOPS improvements for both iodepth=1 and iodepth=32 35 * workloads. 36 */ 37 #define IOTHREAD_POLL_MAX_NS_DEFAULT 32768ULL 38 #else 39 #define IOTHREAD_POLL_MAX_NS_DEFAULT 0ULL 40 #endif 41 42 static __thread IOThread *my_iothread; 43 44 AioContext *qemu_get_current_aio_context(void) 45 { 46 return my_iothread ? my_iothread->ctx : qemu_get_aio_context(); 47 } 48 49 static void *iothread_run(void *opaque) 50 { 51 IOThread *iothread = opaque; 52 53 rcu_register_thread(); 54 /* 55 * g_main_context_push_thread_default() must be called before anything 56 * in this new thread uses glib. 57 */ 58 g_main_context_push_thread_default(iothread->worker_context); 59 my_iothread = iothread; 60 iothread->thread_id = qemu_get_thread_id(); 61 qemu_sem_post(&iothread->init_done_sem); 62 63 while (iothread->running) { 64 /* 65 * Note: from functional-wise the g_main_loop_run() below can 66 * already cover the aio_poll() events, but we can't run the 67 * main loop unconditionally because explicit aio_poll() here 68 * is faster than g_main_loop_run() when we do not need the 69 * gcontext at all (e.g., pure block layer iothreads). In 70 * other words, when we want to run the gcontext with the 71 * iothread we need to pay some performance for functionality. 72 */ 73 aio_poll(iothread->ctx, true); 74 75 /* 76 * We must check the running state again in case it was 77 * changed in previous aio_poll() 78 */ 79 if (iothread->running && atomic_read(&iothread->run_gcontext)) { 80 g_main_loop_run(iothread->main_loop); 81 } 82 } 83 84 g_main_context_pop_thread_default(iothread->worker_context); 85 rcu_unregister_thread(); 86 return NULL; 87 } 88 89 /* Runs in iothread_run() thread */ 90 static void iothread_stop_bh(void *opaque) 91 { 92 IOThread *iothread = opaque; 93 94 iothread->running = false; /* stop iothread_run() */ 95 96 if (iothread->main_loop) { 97 g_main_loop_quit(iothread->main_loop); 98 } 99 } 100 101 void iothread_stop(IOThread *iothread) 102 { 103 if (!iothread->ctx || iothread->stopping) { 104 return; 105 } 106 iothread->stopping = true; 107 aio_bh_schedule_oneshot(iothread->ctx, iothread_stop_bh, iothread); 108 qemu_thread_join(&iothread->thread); 109 } 110 111 static void iothread_instance_init(Object *obj) 112 { 113 IOThread *iothread = IOTHREAD(obj); 114 115 iothread->poll_max_ns = IOTHREAD_POLL_MAX_NS_DEFAULT; 116 iothread->thread_id = -1; 117 qemu_sem_init(&iothread->init_done_sem, 0); 118 /* By default, we don't run gcontext */ 119 atomic_set(&iothread->run_gcontext, 0); 120 } 121 122 static void iothread_instance_finalize(Object *obj) 123 { 124 IOThread *iothread = IOTHREAD(obj); 125 126 iothread_stop(iothread); 127 128 /* 129 * Before glib2 2.33.10, there is a glib2 bug that GSource context 130 * pointer may not be cleared even if the context has already been 131 * destroyed (while it should). Here let's free the AIO context 132 * earlier to bypass that glib bug. 133 * 134 * We can remove this comment after the minimum supported glib2 135 * version boosts to 2.33.10. Before that, let's free the 136 * GSources first before destroying any GMainContext. 137 */ 138 if (iothread->ctx) { 139 aio_context_unref(iothread->ctx); 140 iothread->ctx = NULL; 141 } 142 if (iothread->worker_context) { 143 g_main_context_unref(iothread->worker_context); 144 iothread->worker_context = NULL; 145 g_main_loop_unref(iothread->main_loop); 146 iothread->main_loop = NULL; 147 } 148 qemu_sem_destroy(&iothread->init_done_sem); 149 } 150 151 static void iothread_init_gcontext(IOThread *iothread) 152 { 153 GSource *source; 154 155 iothread->worker_context = g_main_context_new(); 156 source = aio_get_g_source(iothread_get_aio_context(iothread)); 157 g_source_attach(source, iothread->worker_context); 158 g_source_unref(source); 159 iothread->main_loop = g_main_loop_new(iothread->worker_context, TRUE); 160 } 161 162 static void iothread_complete(UserCreatable *obj, Error **errp) 163 { 164 Error *local_error = NULL; 165 IOThread *iothread = IOTHREAD(obj); 166 char *thread_name; 167 168 iothread->stopping = false; 169 iothread->running = true; 170 iothread->ctx = aio_context_new(errp); 171 if (!iothread->ctx) { 172 return; 173 } 174 175 /* 176 * Init one GMainContext for the iothread unconditionally, even if 177 * it's not used 178 */ 179 iothread_init_gcontext(iothread); 180 181 aio_context_set_poll_params(iothread->ctx, 182 iothread->poll_max_ns, 183 iothread->poll_grow, 184 iothread->poll_shrink, 185 &local_error); 186 if (local_error) { 187 error_propagate(errp, local_error); 188 aio_context_unref(iothread->ctx); 189 iothread->ctx = NULL; 190 return; 191 } 192 193 /* This assumes we are called from a thread with useful CPU affinity for us 194 * to inherit. 195 */ 196 thread_name = g_strdup_printf("IO %s", 197 object_get_canonical_path_component(OBJECT(obj))); 198 qemu_thread_create(&iothread->thread, thread_name, iothread_run, 199 iothread, QEMU_THREAD_JOINABLE); 200 g_free(thread_name); 201 202 /* Wait for initialization to complete */ 203 while (iothread->thread_id == -1) { 204 qemu_sem_wait(&iothread->init_done_sem); 205 } 206 } 207 208 typedef struct { 209 const char *name; 210 ptrdiff_t offset; /* field's byte offset in IOThread struct */ 211 } PollParamInfo; 212 213 static PollParamInfo poll_max_ns_info = { 214 "poll-max-ns", offsetof(IOThread, poll_max_ns), 215 }; 216 static PollParamInfo poll_grow_info = { 217 "poll-grow", offsetof(IOThread, poll_grow), 218 }; 219 static PollParamInfo poll_shrink_info = { 220 "poll-shrink", offsetof(IOThread, poll_shrink), 221 }; 222 223 static void iothread_get_poll_param(Object *obj, Visitor *v, 224 const char *name, void *opaque, Error **errp) 225 { 226 IOThread *iothread = IOTHREAD(obj); 227 PollParamInfo *info = opaque; 228 int64_t *field = (void *)iothread + info->offset; 229 230 visit_type_int64(v, name, field, errp); 231 } 232 233 static void iothread_set_poll_param(Object *obj, Visitor *v, 234 const char *name, void *opaque, Error **errp) 235 { 236 IOThread *iothread = IOTHREAD(obj); 237 PollParamInfo *info = opaque; 238 int64_t *field = (void *)iothread + info->offset; 239 int64_t value; 240 241 if (!visit_type_int64(v, name, &value, errp)) { 242 return; 243 } 244 245 if (value < 0) { 246 error_setg(errp, "%s value must be in range [0, %" PRId64 "]", 247 info->name, INT64_MAX); 248 return; 249 } 250 251 *field = value; 252 253 if (iothread->ctx) { 254 aio_context_set_poll_params(iothread->ctx, 255 iothread->poll_max_ns, 256 iothread->poll_grow, 257 iothread->poll_shrink, 258 errp); 259 } 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); 271 object_class_property_add(klass, "poll-grow", "int", 272 iothread_get_poll_param, 273 iothread_set_poll_param, 274 NULL, &poll_grow_info); 275 object_class_property_add(klass, "poll-shrink", "int", 276 iothread_get_poll_param, 277 iothread_set_poll_param, 278 NULL, &poll_shrink_info); 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 g_strdup(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 } 378