iothread.c

   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
 179
 180 static void iothread_init(EventLoopBase *base, Error **errp)
 181 {
 182     Error *local_error = NULL;
 183     IOThread *iothread = IOTHREAD(base);
 184     char *thread_name;
 185
 186     iothread->stopping = false;
 187     iothread->running = true;
 188     iothread->ctx = aio_context_new(errp);
 189     if (!iothread->ctx) {
 190         return;
 191     }
 192
 193     /*
 194      * Init one GMainContext for the iothread unconditionally, even if
 195      * it's not used
 196      */
 197     iothread_init_gcontext(iothread);
 198
 199     iothread_set_aio_context_params(base, &local_error);
 200     if (local_error) {
 201         error_propagate(errp, local_error);
 202         aio_context_unref(iothread->ctx);
 203         iothread->ctx = NULL;
 204         return;
 205     }
 206
 207     /* This assumes we are called from a thread with useful CPU affinity for us
 208      * to inherit.
 209      */
 210     thread_name = g_strdup_printf("IO %s",
 211                         object_get_canonical_path_component(OBJECT(base)));
 212     qemu_thread_create(&iothread->thread, thread_name, iothread_run,
 213                        iothread, QEMU_THREAD_JOINABLE);
 214     g_free(thread_name);
 215
 216     /* Wait for initialization to complete */
 217     while (iothread->thread_id == -1) {
 218         qemu_sem_wait(&iothread->init_done_sem);
 219     }
 220 }
 221
 222 typedef struct {
 223     const char *name;
 224     ptrdiff_t offset; /* field's byte offset in IOThread struct */
 225 } IOThreadParamInfo;
 226
 227 static IOThreadParamInfo poll_max_ns_info = {
 228     "poll-max-ns", offsetof(IOThread, poll_max_ns),
 229 };
 230 static IOThreadParamInfo poll_grow_info = {
 231     "poll-grow", offsetof(IOThread, poll_grow),
 232 };
 233 static IOThreadParamInfo poll_shrink_info = {
 234     "poll-shrink", offsetof(IOThread, poll_shrink),
 235 };
 236
 237 static void iothread_get_param(Object *obj, Visitor *v,
 238         const char *name, IOThreadParamInfo *info, Error **errp)
 239 {
 240     IOThread *iothread = IOTHREAD(obj);
 241     int64_t *field = (void *)iothread + info->offset;
 242
 243     visit_type_int64(v, name, field, errp);
 244 }
 245
 246 static bool iothread_set_param(Object *obj, Visitor *v,
 247         const char *name, IOThreadParamInfo *info, Error **errp)
 248 {
 249     IOThread *iothread = IOTHREAD(obj);
 250     int64_t *field = (void *)iothread + info->offset;
 251     int64_t value;
 252
 253     if (!visit_type_int64(v, name, &value, errp)) {
 254         return false;
 255     }
 256
 257     if (value < 0) {
 258         error_setg(errp, "%s value must be in range [0, %" PRId64 "]",
 259                    info->name, INT64_MAX);
 260         return false;
 261     }
 262
 263     *field = value;
 264
 265     return true;
 266 }
 267
 268 static void iothread_get_poll_param(Object *obj, Visitor *v,
 269         const char *name, void *opaque, Error **errp)
 270 {
 271     IOThreadParamInfo *info = opaque;
 272
 273     iothread_get_param(obj, v, name, info, errp);
 274 }
 275
 276 static void iothread_set_poll_param(Object *obj, Visitor *v,
 277         const char *name, void *opaque, Error **errp)
 278 {
 279     IOThread *iothread = IOTHREAD(obj);
 280     IOThreadParamInfo *info = opaque;
 281
 282     if (!iothread_set_param(obj, v, name, info, errp)) {
 283         return;
 284     }
 285
 286     if (iothread->ctx) {
 287         aio_context_set_poll_params(iothread->ctx,
 288                                     iothread->poll_max_ns,
 289                                     iothread->poll_grow,
 290                                     iothread->poll_shrink,
 291                                     errp);
 292     }
 293 }
 294
 295 static void iothread_class_init(ObjectClass *klass, void *class_data)
 296 {
 297     EventLoopBaseClass *bc = EVENT_LOOP_BASE_CLASS(klass);
 298
 299     bc->init = iothread_init;
 300     bc->update_params = iothread_set_aio_context_params;
 301
 302     object_class_property_add(klass, "poll-max-ns", "int",
 303                               iothread_get_poll_param,
 304                               iothread_set_poll_param,
 305                               NULL, &poll_max_ns_info);
 306     object_class_property_add(klass, "poll-grow", "int",
 307                               iothread_get_poll_param,
 308                               iothread_set_poll_param,
 309                               NULL, &poll_grow_info);
 310     object_class_property_add(klass, "poll-shrink", "int",
 311                               iothread_get_poll_param,
 312                               iothread_set_poll_param,
 313                               NULL, &poll_shrink_info);
 314 }
 315
 316 static const TypeInfo iothread_info = {
 317     .name = TYPE_IOTHREAD,
 318     .parent = TYPE_EVENT_LOOP_BASE,
 319     .class_init = iothread_class_init,
 320     .instance_size = sizeof(IOThread),
 321     .instance_init = iothread_instance_init,
 322     .instance_finalize = iothread_instance_finalize,
 323 };
 324
 325 static void iothread_register_types(void)
 326 {
 327     type_register_static(&iothread_info);
 328 }
 329
 330 type_init(iothread_register_types)
 331
 332 char *iothread_get_id(IOThread *iothread)
 333 {
 334     return g_strdup(object_get_canonical_path_component(OBJECT(iothread)));
 335 }
 336
 337 AioContext *iothread_get_aio_context(IOThread *iothread)
 338 {
 339     return iothread->ctx;
 340 }
 341
 342 static int query_one_iothread(Object *object, void *opaque)
 343 {
 344     IOThreadInfoList ***tail = opaque;
 345     IOThreadInfo *info;
 346     IOThread *iothread;
 347
 348     iothread = (IOThread *)object_dynamic_cast(object, TYPE_IOTHREAD);
 349     if (!iothread) {
 350         return 0;
 351     }
 352
 353     info = g_new0(IOThreadInfo, 1);
 354     info->id = iothread_get_id(iothread);
 355     info->thread_id = iothread->thread_id;
 356     info->poll_max_ns = iothread->poll_max_ns;
 357     info->poll_grow = iothread->poll_grow;
 358     info->poll_shrink = iothread->poll_shrink;
 359     info->aio_max_batch = iothread->parent_obj.aio_max_batch;
 360
 361     QAPI_LIST_APPEND(*tail, info);
 362     return 0;
 363 }
 364
 365 IOThreadInfoList *qmp_query_iothreads(Error **errp)
 366 {
 367     IOThreadInfoList *head = NULL;
 368     IOThreadInfoList **prev = &head;
 369     Object *container = object_get_objects_root();
 370
 371     object_child_foreach(container, query_one_iothread, &prev);
 372     return head;
 373 }
 374
 375 GMainContext *iothread_get_g_main_context(IOThread *iothread)
 376 {
 377     qatomic_set(&iothread->run_gcontext, 1);
 378     aio_notify(iothread->ctx);
 379     return iothread->worker_context;
 380 }
 381
 382 IOThread *iothread_create(const char *id, Error **errp)
 383 {
 384     Object *obj;
 385
 386     obj = object_new_with_props(TYPE_IOTHREAD,
 387                                 object_get_internal_root(),
 388                                 id, errp, NULL);
 389
 390     return IOTHREAD(obj);
 391 }
 392
 393 void iothread_destroy(IOThread *iothread)
 394 {
 395     object_unparent(OBJECT(iothread));
 396 }
 397
 398 /* Lookup IOThread by its id.  Only finds user-created objects, not internal
 399  * iothread_create() objects. */
 400 IOThread *iothread_by_id(const char *id)
 401 {
 402     return IOTHREAD(object_resolve_path_type(id, TYPE_IOTHREAD, NULL));
 403 }
 404
 405 bool qemu_in_iothread(void)
 406 {
 407     return qemu_get_current_aio_context() == qemu_get_aio_context() ?
 408                     false : true;
 409 }