1 /* 2 * Event loop thread 3 * 4 * Copyright Red Hat Inc., 2013, 2020 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/event-loop-base.h" 21 #include "sysemu/iothread.h" 22 #include "qapi/error.h" 23 #include "qapi/qapi-commands-misc.h" 24 #include "qemu/error-report.h" 25 #include "qemu/rcu.h" 26 #include "qemu/main-loop.h" 27 28 typedef ObjectClass IOThreadClass; 29 30 DECLARE_CLASS_CHECKERS(IOThreadClass, IOTHREAD, 31 TYPE_IOTHREAD) 32 33 #ifdef CONFIG_POSIX 34 /* Benchmark results from 2016 on NVMe SSD drives show max polling times around 35 * 16-32 microseconds yield IOPS improvements for both iodepth=1 and iodepth=32 36 * workloads. 37 */ 38 #define IOTHREAD_POLL_MAX_NS_DEFAULT 32768ULL 39 #else 40 #define IOTHREAD_POLL_MAX_NS_DEFAULT 0ULL 41 #endif 42 43 static void *iothread_run(void *opaque) 44 { 45 IOThread *iothread = opaque; 46 47 rcu_register_thread(); 48 /* 49 * g_main_context_push_thread_default() must be called before anything 50 * in this new thread uses glib. 51 */ 52 g_main_context_push_thread_default(iothread->worker_context); 53 qemu_set_current_aio_context(iothread->ctx); 54 iothread->thread_id = qemu_get_thread_id(); 55 qemu_sem_post(&iothread->init_done_sem); 56 57 while (iothread->running) { 58 /* 59 * Note: from functional-wise the g_main_loop_run() below can 60 * already cover the aio_poll() events, but we can't run the 61 * main loop unconditionally because explicit aio_poll() here 62 * is faster than g_main_loop_run() when we do not need the 63 * gcontext at all (e.g., pure block layer iothreads). In 64 * other words, when we want to run the gcontext with the 65 * iothread we need to pay some performance for functionality. 66 */ 67 aio_poll(iothread->ctx, true); 68 69 /* 70 * We must check the running state again in case it was 71 * changed in previous aio_poll() 72 */ 73 if (iothread->running && qatomic_read(&iothread->run_gcontext)) { 74 g_main_loop_run(iothread->main_loop); 75 } 76 } 77 78 g_main_context_pop_thread_default(iothread->worker_context); 79 rcu_unregister_thread(); 80 return NULL; 81 } 82 83 /* Runs in iothread_run() thread */ 84 static void iothread_stop_bh(void *opaque) 85 { 86 IOThread *iothread = opaque; 87 88 iothread->running = false; /* stop iothread_run() */ 89 90 if (iothread->main_loop) { 91 g_main_loop_quit(iothread->main_loop); 92 } 93 } 94 95 void iothread_stop(IOThread *iothread) 96 { 97 if (!iothread->ctx || iothread->stopping) { 98 return; 99 } 100 iothread->stopping = true; 101 aio_bh_schedule_oneshot(iothread->ctx, iothread_stop_bh, iothread); 102 qemu_thread_join(&iothread->thread); 103 } 104 105 static void iothread_instance_init(Object *obj) 106 { 107 IOThread *iothread = IOTHREAD(obj); 108 109 iothread->poll_max_ns = IOTHREAD_POLL_MAX_NS_DEFAULT; 110 iothread->thread_id = -1; 111 qemu_sem_init(&iothread->init_done_sem, 0); 112 /* By default, we don't run gcontext */ 113 qatomic_set(&iothread->run_gcontext, 0); 114 } 115 116 static void iothread_instance_finalize(Object *obj) 117 { 118 IOThread *iothread = IOTHREAD(obj); 119 120 iothread_stop(iothread); 121 122 /* 123 * Before glib2 2.33.10, there is a glib2 bug that GSource context 124 * pointer may not be cleared even if the context has already been 125 * destroyed (while it should). Here let's free the AIO context 126 * earlier to bypass that glib bug. 127 * 128 * We can remove this comment after the minimum supported glib2 129 * version boosts to 2.33.10. Before that, let's free the 130 * GSources first before destroying any GMainContext. 131 */ 132 if (iothread->ctx) { 133 aio_context_unref(iothread->ctx); 134 iothread->ctx = NULL; 135 } 136 if (iothread->worker_context) { 137 g_main_context_unref(iothread->worker_context); 138 iothread->worker_context = NULL; 139 g_main_loop_unref(iothread->main_loop); 140 iothread->main_loop = NULL; 141 } 142 qemu_sem_destroy(&iothread->init_done_sem); 143 } 144 145 static void iothread_init_gcontext(IOThread *iothread) 146 { 147 GSource *source; 148 149 iothread->worker_context = g_main_context_new(); 150 source = aio_get_g_source(iothread_get_aio_context(iothread)); 151 g_source_attach(source, iothread->worker_context); 152 g_source_unref(source); 153 iothread->main_loop = g_main_loop_new(iothread->worker_context, TRUE); 154 } 155 156 static void iothread_set_aio_context_params(EventLoopBase *base, Error **errp) 157 { 158 IOThread *iothread = IOTHREAD(base); 159 ERRP_GUARD(); 160 161 if (!iothread->ctx) { 162 return; 163 } 164 165 aio_context_set_poll_params(iothread->ctx, 166 iothread->poll_max_ns, 167 iothread->poll_grow, 168 iothread->poll_shrink, 169 errp); 170 if (*errp) { 171 return; 172 } 173 174 aio_context_set_aio_params(iothread->ctx, 175 iothread->parent_obj.aio_max_batch, 176 errp); 177 178 aio_context_set_thread_pool_params(iothread->ctx, base->thread_pool_min, 179 base->thread_pool_max, errp); 180 } 181 182 183 static void iothread_init(EventLoopBase *base, Error **errp) 184 { 185 Error *local_error = NULL; 186 IOThread *iothread = IOTHREAD(base); 187 char *thread_name; 188 189 iothread->stopping = false; 190 iothread->running = true; 191 iothread->ctx = aio_context_new(errp); 192 if (!iothread->ctx) { 193 return; 194 } 195 196 /* 197 * Init one GMainContext for the iothread unconditionally, even if 198 * it's not used 199 */ 200 iothread_init_gcontext(iothread); 201 202 iothread_set_aio_context_params(base, &local_error); 203 if (local_error) { 204 error_propagate(errp, local_error); 205 aio_context_unref(iothread->ctx); 206 iothread->ctx = NULL; 207 return; 208 } 209 210 /* This assumes we are called from a thread with useful CPU affinity for us 211 * to inherit. 212 */ 213 thread_name = g_strdup_printf("IO %s", 214 object_get_canonical_path_component(OBJECT(base))); 215 qemu_thread_create(&iothread->thread, thread_name, iothread_run, 216 iothread, QEMU_THREAD_JOINABLE); 217 g_free(thread_name); 218 219 /* Wait for initialization to complete */ 220 while (iothread->thread_id == -1) { 221 qemu_sem_wait(&iothread->init_done_sem); 222 } 223 } 224 225 typedef struct { 226 const char *name; 227 ptrdiff_t offset; /* field's byte offset in IOThread struct */ 228 } IOThreadParamInfo; 229 230 static IOThreadParamInfo poll_max_ns_info = { 231 "poll-max-ns", offsetof(IOThread, poll_max_ns), 232 }; 233 static IOThreadParamInfo poll_grow_info = { 234 "poll-grow", offsetof(IOThread, poll_grow), 235 }; 236 static IOThreadParamInfo poll_shrink_info = { 237 "poll-shrink", offsetof(IOThread, poll_shrink), 238 }; 239 240 static void iothread_get_param(Object *obj, Visitor *v, 241 const char *name, IOThreadParamInfo *info, Error **errp) 242 { 243 IOThread *iothread = IOTHREAD(obj); 244 int64_t *field = (void *)iothread + info->offset; 245 246 visit_type_int64(v, name, field, errp); 247 } 248 249 static bool iothread_set_param(Object *obj, Visitor *v, 250 const char *name, IOThreadParamInfo *info, Error **errp) 251 { 252 IOThread *iothread = IOTHREAD(obj); 253 int64_t *field = (void *)iothread + info->offset; 254 int64_t value; 255 256 if (!visit_type_int64(v, name, &value, errp)) { 257 return false; 258 } 259 260 if (value < 0) { 261 error_setg(errp, "%s value must be in range [0, %" PRId64 "]", 262 info->name, INT64_MAX); 263 return false; 264 } 265 266 *field = value; 267 268 return true; 269 } 270 271 static void iothread_get_poll_param(Object *obj, Visitor *v, 272 const char *name, void *opaque, Error **errp) 273 { 274 IOThreadParamInfo *info = opaque; 275 276 iothread_get_param(obj, v, name, info, errp); 277 } 278 279 static void iothread_set_poll_param(Object *obj, Visitor *v, 280 const char *name, void *opaque, Error **errp) 281 { 282 IOThread *iothread = IOTHREAD(obj); 283 IOThreadParamInfo *info = opaque; 284 285 if (!iothread_set_param(obj, v, name, info, errp)) { 286 return; 287 } 288 289 if (iothread->ctx) { 290 aio_context_set_poll_params(iothread->ctx, 291 iothread->poll_max_ns, 292 iothread->poll_grow, 293 iothread->poll_shrink, 294 errp); 295 } 296 } 297 298 static void iothread_class_init(ObjectClass *klass, void *class_data) 299 { 300 EventLoopBaseClass *bc = EVENT_LOOP_BASE_CLASS(klass); 301 302 bc->init = iothread_init; 303 bc->update_params = iothread_set_aio_context_params; 304 305 object_class_property_add(klass, "poll-max-ns", "int", 306 iothread_get_poll_param, 307 iothread_set_poll_param, 308 NULL, &poll_max_ns_info); 309 object_class_property_add(klass, "poll-grow", "int", 310 iothread_get_poll_param, 311 iothread_set_poll_param, 312 NULL, &poll_grow_info); 313 object_class_property_add(klass, "poll-shrink", "int", 314 iothread_get_poll_param, 315 iothread_set_poll_param, 316 NULL, &poll_shrink_info); 317 } 318 319 static const TypeInfo iothread_info = { 320 .name = TYPE_IOTHREAD, 321 .parent = TYPE_EVENT_LOOP_BASE, 322 .class_init = iothread_class_init, 323 .instance_size = sizeof(IOThread), 324 .instance_init = iothread_instance_init, 325 .instance_finalize = iothread_instance_finalize, 326 }; 327 328 static void iothread_register_types(void) 329 { 330 type_register_static(&iothread_info); 331 } 332 333 type_init(iothread_register_types) 334 335 char *iothread_get_id(IOThread *iothread) 336 { 337 return g_strdup(object_get_canonical_path_component(OBJECT(iothread))); 338 } 339 340 AioContext *iothread_get_aio_context(IOThread *iothread) 341 { 342 return iothread->ctx; 343 } 344 345 static int query_one_iothread(Object *object, void *opaque) 346 { 347 IOThreadInfoList ***tail = opaque; 348 IOThreadInfo *info; 349 IOThread *iothread; 350 351 iothread = (IOThread *)object_dynamic_cast(object, TYPE_IOTHREAD); 352 if (!iothread) { 353 return 0; 354 } 355 356 info = g_new0(IOThreadInfo, 1); 357 info->id = iothread_get_id(iothread); 358 info->thread_id = iothread->thread_id; 359 info->poll_max_ns = iothread->poll_max_ns; 360 info->poll_grow = iothread->poll_grow; 361 info->poll_shrink = iothread->poll_shrink; 362 info->aio_max_batch = iothread->parent_obj.aio_max_batch; 363 364 QAPI_LIST_APPEND(*tail, info); 365 return 0; 366 } 367 368 IOThreadInfoList *qmp_query_iothreads(Error **errp) 369 { 370 IOThreadInfoList *head = NULL; 371 IOThreadInfoList **prev = &head; 372 Object *container = object_get_objects_root(); 373 374 object_child_foreach(container, query_one_iothread, &prev); 375 return head; 376 } 377 378 GMainContext *iothread_get_g_main_context(IOThread *iothread) 379 { 380 qatomic_set(&iothread->run_gcontext, 1); 381 aio_notify(iothread->ctx); 382 return iothread->worker_context; 383 } 384 385 IOThread *iothread_create(const char *id, Error **errp) 386 { 387 Object *obj; 388 389 obj = object_new_with_props(TYPE_IOTHREAD, 390 object_get_internal_root(), 391 id, errp, NULL); 392 393 return IOTHREAD(obj); 394 } 395 396 void iothread_destroy(IOThread *iothread) 397 { 398 object_unparent(OBJECT(iothread)); 399 } 400 401 /* Lookup IOThread by its id. Only finds user-created objects, not internal 402 * iothread_create() objects. */ 403 IOThread *iothread_by_id(const char *id) 404 { 405 return IOTHREAD(object_resolve_path_type(id, TYPE_IOTHREAD, NULL)); 406 } 407 408 bool qemu_in_iothread(void) 409 { 410 return qemu_get_current_aio_context() == qemu_get_aio_context() ? 411 false : true; 412 } 413