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