iothread.c

   1 /*
   2  * Event loop thread
   3  *
   4  * Copyright Red Hat Inc., 2013
   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 "qmp-commands.h"
  22 #include "qemu/error-report.h"
  23 #include "qemu/rcu.h"
  24 #include "qemu/main-loop.h"
  25
  26 typedef ObjectClass IOThreadClass;
  27
  28 #define IOTHREAD_GET_CLASS(obj) \
  29    OBJECT_GET_CLASS(IOThreadClass, obj, TYPE_IOTHREAD)
  30 #define IOTHREAD_CLASS(klass) \
  31    OBJECT_CLASS_CHECK(IOThreadClass, klass, TYPE_IOTHREAD)
  32
  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
  39 static __thread IOThread *my_iothread;
  40
  41 AioContext *qemu_get_current_aio_context(void)
  42 {
  43     return my_iothread ? my_iothread->ctx : qemu_get_aio_context();
  44 }
  45
  46 static void *iothread_run(void *opaque)
  47 {
  48     IOThread *iothread = opaque;
  49
  50     rcu_register_thread();
  51
  52     my_iothread = iothread;
  53     qemu_mutex_lock(&iothread->init_done_lock);
  54     iothread->thread_id = qemu_get_thread_id();
  55     qemu_cond_signal(&iothread->init_done_cond);
  56     qemu_mutex_unlock(&iothread->init_done_lock);
  57
  58     while (!atomic_read(&iothread->stopping)) {
  59         aio_poll(iothread->ctx, true);
  60     }
  61
  62     rcu_unregister_thread();
  63     return NULL;
  64 }
  65
  66 static int iothread_stop(Object *object, void *opaque)
  67 {
  68     IOThread *iothread;
  69
  70     iothread = (IOThread *)object_dynamic_cast(object, TYPE_IOTHREAD);
  71     if (!iothread || !iothread->ctx) {
  72         return 0;
  73     }
  74     iothread->stopping = true;
  75     aio_notify(iothread->ctx);
  76     qemu_thread_join(&iothread->thread);
  77     return 0;
  78 }
  79
  80 static void iothread_instance_init(Object *obj)
  81 {
  82     IOThread *iothread = IOTHREAD(obj);
  83
  84     iothread->poll_max_ns = IOTHREAD_POLL_MAX_NS_DEFAULT;
  85 }
  86
  87 static void iothread_instance_finalize(Object *obj)
  88 {
  89     IOThread *iothread = IOTHREAD(obj);
  90
  91     iothread_stop(obj, NULL);
  92     qemu_cond_destroy(&iothread->init_done_cond);
  93     qemu_mutex_destroy(&iothread->init_done_lock);
  94     if (!iothread->ctx) {
  95         return;
  96     }
  97     aio_context_unref(iothread->ctx);
  98 }
  99
 100 static void iothread_complete(UserCreatable *obj, Error **errp)
 101 {
 102     Error *local_error = NULL;
 103     IOThread *iothread = IOTHREAD(obj);
 104     char *name, *thread_name;
 105
 106     iothread->stopping = false;
 107     iothread->thread_id = -1;
 108     iothread->ctx = aio_context_new(&local_error);
 109     if (!iothread->ctx) {
 110         error_propagate(errp, local_error);
 111         return;
 112     }
 113
 114     aio_context_set_poll_params(iothread->ctx,
 115                                 iothread->poll_max_ns,
 116                                 iothread->poll_grow,
 117                                 iothread->poll_shrink,
 118                                 &local_error);
 119     if (local_error) {
 120         error_propagate(errp, local_error);
 121         aio_context_unref(iothread->ctx);
 122         iothread->ctx = NULL;
 123         return;
 124     }
 125
 126     qemu_mutex_init(&iothread->init_done_lock);
 127     qemu_cond_init(&iothread->init_done_cond);
 128
 129     /* This assumes we are called from a thread with useful CPU affinity for us
 130      * to inherit.
 131      */
 132     name = object_get_canonical_path_component(OBJECT(obj));
 133     thread_name = g_strdup_printf("IO %s", name);
 134     qemu_thread_create(&iothread->thread, thread_name, iothread_run,
 135                        iothread, QEMU_THREAD_JOINABLE);
 136     g_free(thread_name);
 137     g_free(name);
 138
 139     /* Wait for initialization to complete */
 140     qemu_mutex_lock(&iothread->init_done_lock);
 141     while (iothread->thread_id == -1) {
 142         qemu_cond_wait(&iothread->init_done_cond,
 143                        &iothread->init_done_lock);
 144     }
 145     qemu_mutex_unlock(&iothread->init_done_lock);
 146 }
 147
 148 typedef struct {
 149     const char *name;
 150     ptrdiff_t offset; /* field's byte offset in IOThread struct */
 151 } PollParamInfo;
 152
 153 static PollParamInfo poll_max_ns_info = {
 154     "poll-max-ns", offsetof(IOThread, poll_max_ns),
 155 };
 156 static PollParamInfo poll_grow_info = {
 157     "poll-grow", offsetof(IOThread, poll_grow),
 158 };
 159 static PollParamInfo poll_shrink_info = {
 160     "poll-shrink", offsetof(IOThread, poll_shrink),
 161 };
 162
 163 static void iothread_get_poll_param(Object *obj, Visitor *v,
 164         const char *name, void *opaque, Error **errp)
 165 {
 166     IOThread *iothread = IOTHREAD(obj);
 167     PollParamInfo *info = opaque;
 168     int64_t *field = (void *)iothread + info->offset;
 169
 170     visit_type_int64(v, name, field, errp);
 171 }
 172
 173 static void iothread_set_poll_param(Object *obj, Visitor *v,
 174         const char *name, void *opaque, Error **errp)
 175 {
 176     IOThread *iothread = IOTHREAD(obj);
 177     PollParamInfo *info = opaque;
 178     int64_t *field = (void *)iothread + info->offset;
 179     Error *local_err = NULL;
 180     int64_t value;
 181
 182     visit_type_int64(v, name, &value, &local_err);
 183     if (local_err) {
 184         goto out;
 185     }
 186
 187     if (value < 0) {
 188         error_setg(&local_err, "%s value must be in range [0, %"PRId64"]",
 189                    info->name, INT64_MAX);
 190         goto out;
 191     }
 192
 193     *field = value;
 194
 195     if (iothread->ctx) {
 196         aio_context_set_poll_params(iothread->ctx,
 197                                     iothread->poll_max_ns,
 198                                     iothread->poll_grow,
 199                                     iothread->poll_shrink,
 200                                     &local_err);
 201     }
 202
 203 out:
 204     error_propagate(errp, local_err);
 205 }
 206
 207 static void iothread_class_init(ObjectClass *klass, void *class_data)
 208 {
 209     UserCreatableClass *ucc = USER_CREATABLE_CLASS(klass);
 210     ucc->complete = iothread_complete;
 211
 212     object_class_property_add(klass, "poll-max-ns", "int",
 213                               iothread_get_poll_param,
 214                               iothread_set_poll_param,
 215                               NULL, &poll_max_ns_info, &error_abort);
 216     object_class_property_add(klass, "poll-grow", "int",
 217                               iothread_get_poll_param,
 218                               iothread_set_poll_param,
 219                               NULL, &poll_grow_info, &error_abort);
 220     object_class_property_add(klass, "poll-shrink", "int",
 221                               iothread_get_poll_param,
 222                               iothread_set_poll_param,
 223                               NULL, &poll_shrink_info, &error_abort);
 224 }
 225
 226 static const TypeInfo iothread_info = {
 227     .name = TYPE_IOTHREAD,
 228     .parent = TYPE_OBJECT,
 229     .class_init = iothread_class_init,
 230     .instance_size = sizeof(IOThread),
 231     .instance_init = iothread_instance_init,
 232     .instance_finalize = iothread_instance_finalize,
 233     .interfaces = (InterfaceInfo[]) {
 234         {TYPE_USER_CREATABLE},
 235         {}
 236     },
 237 };
 238
 239 static void iothread_register_types(void)
 240 {
 241     type_register_static(&iothread_info);
 242 }
 243
 244 type_init(iothread_register_types)
 245
 246 char *iothread_get_id(IOThread *iothread)
 247 {
 248     return object_get_canonical_path_component(OBJECT(iothread));
 249 }
 250
 251 AioContext *iothread_get_aio_context(IOThread *iothread)
 252 {
 253     return iothread->ctx;
 254 }
 255
 256 static int query_one_iothread(Object *object, void *opaque)
 257 {
 258     IOThreadInfoList ***prev = opaque;
 259     IOThreadInfoList *elem;
 260     IOThreadInfo *info;
 261     IOThread *iothread;
 262
 263     iothread = (IOThread *)object_dynamic_cast(object, TYPE_IOTHREAD);
 264     if (!iothread) {
 265         return 0;
 266     }
 267
 268     info = g_new0(IOThreadInfo, 1);
 269     info->id = iothread_get_id(iothread);
 270     info->thread_id = iothread->thread_id;
 271     info->poll_max_ns = iothread->poll_max_ns;
 272     info->poll_grow = iothread->poll_grow;
 273     info->poll_shrink = iothread->poll_shrink;
 274
 275     elem = g_new0(IOThreadInfoList, 1);
 276     elem->value = info;
 277     elem->next = NULL;
 278
 279     **prev = elem;
 280     *prev = &elem->next;
 281     return 0;
 282 }
 283
 284 IOThreadInfoList *qmp_query_iothreads(Error **errp)
 285 {
 286     IOThreadInfoList *head = NULL;
 287     IOThreadInfoList **prev = &head;
 288     Object *container = object_get_objects_root();
 289
 290     object_child_foreach(container, query_one_iothread, &prev);
 291     return head;
 292 }
 293
 294 void iothread_stop_all(void)
 295 {
 296     Object *container = object_get_objects_root();
 297     BlockDriverState *bs;
 298     BdrvNextIterator it;
 299
 300     for (bs = bdrv_first(&it); bs; bs = bdrv_next(&it)) {
 301         AioContext *ctx = bdrv_get_aio_context(bs);
 302         if (ctx == qemu_get_aio_context()) {
 303             continue;
 304         }
 305         aio_context_acquire(ctx);
 306         bdrv_set_aio_context(bs, qemu_get_aio_context());
 307         aio_context_release(ctx);
 308     }
 309
 310     object_child_foreach(container, iothread_stop, NULL);
 311 }