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
  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 }