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