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/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 && qatomic_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     qatomic_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 ***tail = opaque;
 314     IOThreadInfo *info;
 315     IOThread *iothread;
 316
 317     iothread = (IOThread *)object_dynamic_cast(object, TYPE_IOTHREAD);
 318     if (!iothread) {
 319         return 0;
 320     }
 321
 322     info = g_new0(IOThreadInfo, 1);
 323     info->id = iothread_get_id(iothread);
 324     info->thread_id = iothread->thread_id;
 325     info->poll_max_ns = iothread->poll_max_ns;
 326     info->poll_grow = iothread->poll_grow;
 327     info->poll_shrink = iothread->poll_shrink;
 328
 329     QAPI_LIST_APPEND(*tail, info);
 330     return 0;
 331 }
 332
 333 IOThreadInfoList *qmp_query_iothreads(Error **errp)
 334 {
 335     IOThreadInfoList *head = NULL;
 336     IOThreadInfoList **prev = &head;
 337     Object *container = object_get_objects_root();
 338
 339     object_child_foreach(container, query_one_iothread, &prev);
 340     return head;
 341 }
 342
 343 GMainContext *iothread_get_g_main_context(IOThread *iothread)
 344 {
 345     qatomic_set(&iothread->run_gcontext, 1);
 346     aio_notify(iothread->ctx);
 347     return iothread->worker_context;
 348 }
 349
 350 IOThread *iothread_create(const char *id, Error **errp)
 351 {
 352     Object *obj;
 353
 354     obj = object_new_with_props(TYPE_IOTHREAD,
 355                                 object_get_internal_root(),
 356                                 id, errp, NULL);
 357
 358     return IOTHREAD(obj);
 359 }
 360
 361 void iothread_destroy(IOThread *iothread)
 362 {
 363     object_unparent(OBJECT(iothread));
 364 }
 365
 366 /* Lookup IOThread by its id.  Only finds user-created objects, not internal
 367  * iothread_create() objects. */
 368 IOThread *iothread_by_id(const char *id)
 369 {
 370     return IOTHREAD(object_resolve_path_type(id, TYPE_IOTHREAD, NULL));
 371 }
 372
 373 bool qemu_in_iothread(void)
 374 {
 375     return qemu_get_current_aio_context() == qemu_get_aio_context() ?
 376                     false : true;
 377 }