qemu

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iothread.c (11900B)

      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     aio_context_set_thread_pool_params(iothread->ctx, base->thread_pool_min,
    179                                        base->thread_pool_max, errp);
    180 }
    181 
    182 
    183 static void iothread_init(EventLoopBase *base, Error **errp)
    184 {
    185     Error *local_error = NULL;
    186     IOThread *iothread = IOTHREAD(base);
    187     char *thread_name;
    188 
    189     iothread->stopping = false;
    190     iothread->running = true;
    191     iothread->ctx = aio_context_new(errp);
    192     if (!iothread->ctx) {
    193         return;
    194     }
    195 
    196     /*
    197      * Init one GMainContext for the iothread unconditionally, even if
    198      * it's not used
    199      */
    200     iothread_init_gcontext(iothread);
    201 
    202     iothread_set_aio_context_params(base, &local_error);
    203     if (local_error) {
    204         error_propagate(errp, local_error);
    205         aio_context_unref(iothread->ctx);
    206         iothread->ctx = NULL;
    207         return;
    208     }
    209 
    210     /* This assumes we are called from a thread with useful CPU affinity for us
    211      * to inherit.
    212      */
    213     thread_name = g_strdup_printf("IO %s",
    214                         object_get_canonical_path_component(OBJECT(base)));
    215     qemu_thread_create(&iothread->thread, thread_name, iothread_run,
    216                        iothread, QEMU_THREAD_JOINABLE);
    217     g_free(thread_name);
    218 
    219     /* Wait for initialization to complete */
    220     while (iothread->thread_id == -1) {
    221         qemu_sem_wait(&iothread->init_done_sem);
    222     }
    223 }
    224 
    225 typedef struct {
    226     const char *name;
    227     ptrdiff_t offset; /* field's byte offset in IOThread struct */
    228 } IOThreadParamInfo;
    229 
    230 static IOThreadParamInfo poll_max_ns_info = {
    231     "poll-max-ns", offsetof(IOThread, poll_max_ns),
    232 };
    233 static IOThreadParamInfo poll_grow_info = {
    234     "poll-grow", offsetof(IOThread, poll_grow),
    235 };
    236 static IOThreadParamInfo poll_shrink_info = {
    237     "poll-shrink", offsetof(IOThread, poll_shrink),
    238 };
    239 
    240 static void iothread_get_param(Object *obj, Visitor *v,
    241         const char *name, IOThreadParamInfo *info, Error **errp)
    242 {
    243     IOThread *iothread = IOTHREAD(obj);
    244     int64_t *field = (void *)iothread + info->offset;
    245 
    246     visit_type_int64(v, name, field, errp);
    247 }
    248 
    249 static bool iothread_set_param(Object *obj, Visitor *v,
    250         const char *name, IOThreadParamInfo *info, Error **errp)
    251 {
    252     IOThread *iothread = IOTHREAD(obj);
    253     int64_t *field = (void *)iothread + info->offset;
    254     int64_t value;
    255 
    256     if (!visit_type_int64(v, name, &value, errp)) {
    257         return false;
    258     }
    259 
    260     if (value < 0) {
    261         error_setg(errp, "%s value must be in range [0, %" PRId64 "]",
    262                    info->name, INT64_MAX);
    263         return false;
    264     }
    265 
    266     *field = value;
    267 
    268     return true;
    269 }
    270 
    271 static void iothread_get_poll_param(Object *obj, Visitor *v,
    272         const char *name, void *opaque, Error **errp)
    273 {
    274     IOThreadParamInfo *info = opaque;
    275 
    276     iothread_get_param(obj, v, name, info, errp);
    277 }
    278 
    279 static void iothread_set_poll_param(Object *obj, Visitor *v,
    280         const char *name, void *opaque, Error **errp)
    281 {
    282     IOThread *iothread = IOTHREAD(obj);
    283     IOThreadParamInfo *info = opaque;
    284 
    285     if (!iothread_set_param(obj, v, name, info, errp)) {
    286         return;
    287     }
    288 
    289     if (iothread->ctx) {
    290         aio_context_set_poll_params(iothread->ctx,
    291                                     iothread->poll_max_ns,
    292                                     iothread->poll_grow,
    293                                     iothread->poll_shrink,
    294                                     errp);
    295     }
    296 }
    297 
    298 static void iothread_class_init(ObjectClass *klass, void *class_data)
    299 {
    300     EventLoopBaseClass *bc = EVENT_LOOP_BASE_CLASS(klass);
    301 
    302     bc->init = iothread_init;
    303     bc->update_params = iothread_set_aio_context_params;
    304 
    305     object_class_property_add(klass, "poll-max-ns", "int",
    306                               iothread_get_poll_param,
    307                               iothread_set_poll_param,
    308                               NULL, &poll_max_ns_info);
    309     object_class_property_add(klass, "poll-grow", "int",
    310                               iothread_get_poll_param,
    311                               iothread_set_poll_param,
    312                               NULL, &poll_grow_info);
    313     object_class_property_add(klass, "poll-shrink", "int",
    314                               iothread_get_poll_param,
    315                               iothread_set_poll_param,
    316                               NULL, &poll_shrink_info);
    317 }
    318 
    319 static const TypeInfo iothread_info = {
    320     .name = TYPE_IOTHREAD,
    321     .parent = TYPE_EVENT_LOOP_BASE,
    322     .class_init = iothread_class_init,
    323     .instance_size = sizeof(IOThread),
    324     .instance_init = iothread_instance_init,
    325     .instance_finalize = iothread_instance_finalize,
    326 };
    327 
    328 static void iothread_register_types(void)
    329 {
    330     type_register_static(&iothread_info);
    331 }
    332 
    333 type_init(iothread_register_types)
    334 
    335 char *iothread_get_id(IOThread *iothread)
    336 {
    337     return g_strdup(object_get_canonical_path_component(OBJECT(iothread)));
    338 }
    339 
    340 AioContext *iothread_get_aio_context(IOThread *iothread)
    341 {
    342     return iothread->ctx;
    343 }
    344 
    345 static int query_one_iothread(Object *object, void *opaque)
    346 {
    347     IOThreadInfoList ***tail = opaque;
    348     IOThreadInfo *info;
    349     IOThread *iothread;
    350 
    351     iothread = (IOThread *)object_dynamic_cast(object, TYPE_IOTHREAD);
    352     if (!iothread) {
    353         return 0;
    354     }
    355 
    356     info = g_new0(IOThreadInfo, 1);
    357     info->id = iothread_get_id(iothread);
    358     info->thread_id = iothread->thread_id;
    359     info->poll_max_ns = iothread->poll_max_ns;
    360     info->poll_grow = iothread->poll_grow;
    361     info->poll_shrink = iothread->poll_shrink;
    362     info->aio_max_batch = iothread->parent_obj.aio_max_batch;
    363 
    364     QAPI_LIST_APPEND(*tail, info);
    365     return 0;
    366 }
    367 
    368 IOThreadInfoList *qmp_query_iothreads(Error **errp)
    369 {
    370     IOThreadInfoList *head = NULL;
    371     IOThreadInfoList **prev = &head;
    372     Object *container = object_get_objects_root();
    373 
    374     object_child_foreach(container, query_one_iothread, &prev);
    375     return head;
    376 }
    377 
    378 GMainContext *iothread_get_g_main_context(IOThread *iothread)
    379 {
    380     qatomic_set(&iothread->run_gcontext, 1);
    381     aio_notify(iothread->ctx);
    382     return iothread->worker_context;
    383 }
    384 
    385 IOThread *iothread_create(const char *id, Error **errp)
    386 {
    387     Object *obj;
    388 
    389     obj = object_new_with_props(TYPE_IOTHREAD,
    390                                 object_get_internal_root(),
    391                                 id, errp, NULL);
    392 
    393     return IOTHREAD(obj);
    394 }
    395 
    396 void iothread_destroy(IOThread *iothread)
    397 {
    398     object_unparent(OBJECT(iothread));
    399 }
    400 
    401 /* Lookup IOThread by its id.  Only finds user-created objects, not internal
    402  * iothread_create() objects. */
    403 IOThread *iothread_by_id(const char *id)
    404 {
    405     return IOTHREAD(object_resolve_path_type(id, TYPE_IOTHREAD, NULL));
    406 }
    407 
    408 bool qemu_in_iothread(void)
    409 {
    410     return qemu_get_current_aio_context() == qemu_get_aio_context() ?
    411                     false : true;
    412 }