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qemu/iothread.c

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/*
* Event loop thread
*
* Copyright Red Hat Inc., 2013
*
* Authors:
* Stefan Hajnoczi <stefanha@redhat.com>
*
* This work is licensed under the terms of the GNU GPL, version 2 or later.
* See the COPYING file in the top-level directory.
*
*/
#include "qemu/osdep.h"
#include "qom/object.h"
#include "qom/object_interfaces.h"
#include "qemu/module.h"
#include "block/aio.h"
#include "block/block.h"
#include "sysemu/iothread.h"
#include "qapi/error.h"
#include "qapi/qapi-commands-misc.h"
#include "qemu/error-report.h"
#include "qemu/rcu.h"
#include "qemu/main-loop.h"
typedef ObjectClass IOThreadClass;
#define IOTHREAD_GET_CLASS(obj) \
OBJECT_GET_CLASS(IOThreadClass, obj, TYPE_IOTHREAD)
#define IOTHREAD_CLASS(klass) \
OBJECT_CLASS_CHECK(IOThreadClass, klass, TYPE_IOTHREAD)
#ifdef CONFIG_POSIX
/* Benchmark results from 2016 on NVMe SSD drives show max polling times around
* 16-32 microseconds yield IOPS improvements for both iodepth=1 and iodepth=32
* workloads.
*/
#define IOTHREAD_POLL_MAX_NS_DEFAULT 32768ULL
#else
#define IOTHREAD_POLL_MAX_NS_DEFAULT 0ULL
#endif
static __thread IOThread *my_iothread;
AioContext *qemu_get_current_aio_context(void)
{
return my_iothread ? my_iothread->ctx : qemu_get_aio_context();
}
static void *iothread_run(void *opaque)
{
IOThread *iothread = opaque;
rcu_register_thread();
/*
* g_main_context_push_thread_default() must be called before anything
* in this new thread uses glib.
*/
g_main_context_push_thread_default(iothread->worker_context);
my_iothread = iothread;
iothread->thread_id = qemu_get_thread_id();
qemu_sem_post(&iothread->init_done_sem);
while (iothread->running) {
/*
* Note: from functional-wise the g_main_loop_run() below can
* already cover the aio_poll() events, but we can't run the
* main loop unconditionally because explicit aio_poll() here
* is faster than g_main_loop_run() when we do not need the
* gcontext at all (e.g., pure block layer iothreads). In
* other words, when we want to run the gcontext with the
* iothread we need to pay some performance for functionality.
*/
aio_poll(iothread->ctx, true);
/*
* We must check the running state again in case it was
* changed in previous aio_poll()
*/
if (iothread->running && atomic_read(&iothread->run_gcontext)) {
g_main_loop_run(iothread->main_loop);
}
}
g_main_context_pop_thread_default(iothread->worker_context);
rcu_unregister_thread();
return NULL;
}
/* Runs in iothread_run() thread */
static void iothread_stop_bh(void *opaque)
{
IOThread *iothread = opaque;
iothread->running = false; /* stop iothread_run() */
if (iothread->main_loop) {
g_main_loop_quit(iothread->main_loop);
}
}
void iothread_stop(IOThread *iothread)
{
if (!iothread->ctx || iothread->stopping) {
return;
}
iothread->stopping = true;
aio_bh_schedule_oneshot(iothread->ctx, iothread_stop_bh, iothread);
qemu_thread_join(&iothread->thread);
}
static void iothread_instance_init(Object *obj)
{
IOThread *iothread = IOTHREAD(obj);
iothread->poll_max_ns = IOTHREAD_POLL_MAX_NS_DEFAULT;
iothread->thread_id = -1;
qemu_sem_init(&iothread->init_done_sem, 0);
/* By default, we don't run gcontext */
atomic_set(&iothread->run_gcontext, 0);
}
static void iothread_instance_finalize(Object *obj)
{
IOThread *iothread = IOTHREAD(obj);
iothread_stop(iothread);
/*
* Before glib2 2.33.10, there is a glib2 bug that GSource context
* pointer may not be cleared even if the context has already been
* destroyed (while it should). Here let's free the AIO context
* earlier to bypass that glib bug.
*
* We can remove this comment after the minimum supported glib2
* version boosts to 2.33.10. Before that, let's free the
* GSources first before destroying any GMainContext.
*/
if (iothread->ctx) {
aio_context_unref(iothread->ctx);
iothread->ctx = NULL;
}
if (iothread->worker_context) {
g_main_context_unref(iothread->worker_context);
iothread->worker_context = NULL;
g_main_loop_unref(iothread->main_loop);
iothread->main_loop = NULL;
}
qemu_sem_destroy(&iothread->init_done_sem);
}
static void iothread_init_gcontext(IOThread *iothread)
{
GSource *source;
iothread->worker_context = g_main_context_new();
source = aio_get_g_source(iothread_get_aio_context(iothread));
g_source_attach(source, iothread->worker_context);
g_source_unref(source);
iothread->main_loop = g_main_loop_new(iothread->worker_context, TRUE);
}
static void iothread_complete(UserCreatable *obj, Error **errp)
{
Error *local_error = NULL;
IOThread *iothread = IOTHREAD(obj);
char *name, *thread_name;
iothread->stopping = false;
iothread->running = true;
iothread->ctx = aio_context_new(&local_error);
if (!iothread->ctx) {
error_propagate(errp, local_error);
return;
}
/*
* Init one GMainContext for the iothread unconditionally, even if
* it's not used
*/
iothread_init_gcontext(iothread);
aio_context_set_poll_params(iothread->ctx,
iothread->poll_max_ns,
iothread->poll_grow,
iothread->poll_shrink,
&local_error);
if (local_error) {
error_propagate(errp, local_error);
aio_context_unref(iothread->ctx);
iothread->ctx = NULL;
return;
}
/* This assumes we are called from a thread with useful CPU affinity for us
* to inherit.
*/
name = object_get_canonical_path_component(OBJECT(obj));
thread_name = g_strdup_printf("IO %s", name);
qemu_thread_create(&iothread->thread, thread_name, iothread_run,
iothread, QEMU_THREAD_JOINABLE);
g_free(thread_name);
g_free(name);
/* Wait for initialization to complete */
while (iothread->thread_id == -1) {
qemu_sem_wait(&iothread->init_done_sem);
}
}
typedef struct {
const char *name;
ptrdiff_t offset; /* field's byte offset in IOThread struct */
} PollParamInfo;
static PollParamInfo poll_max_ns_info = {
"poll-max-ns", offsetof(IOThread, poll_max_ns),
};
static PollParamInfo poll_grow_info = {
"poll-grow", offsetof(IOThread, poll_grow),
};
static PollParamInfo poll_shrink_info = {
"poll-shrink", offsetof(IOThread, poll_shrink),
};
static void iothread_get_poll_param(Object *obj, Visitor *v,
const char *name, void *opaque, Error **errp)
{
IOThread *iothread = IOTHREAD(obj);
PollParamInfo *info = opaque;
int64_t *field = (void *)iothread + info->offset;
visit_type_int64(v, name, field, errp);
}
static void iothread_set_poll_param(Object *obj, Visitor *v,
const char *name, void *opaque, Error **errp)
{
IOThread *iothread = IOTHREAD(obj);
PollParamInfo *info = opaque;
int64_t *field = (void *)iothread + info->offset;
Error *local_err = NULL;
int64_t value;
visit_type_int64(v, name, &value, &local_err);
if (local_err) {
goto out;
}
if (value < 0) {
error_setg(&local_err, "%s value must be in range [0, %"PRId64"]",
info->name, INT64_MAX);
goto out;
}
*field = value;
if (iothread->ctx) {
aio_context_set_poll_params(iothread->ctx,
iothread->poll_max_ns,
iothread->poll_grow,
iothread->poll_shrink,
&local_err);
}
out:
error_propagate(errp, local_err);
}
static void iothread_class_init(ObjectClass *klass, void *class_data)
{
UserCreatableClass *ucc = USER_CREATABLE_CLASS(klass);
ucc->complete = iothread_complete;
object_class_property_add(klass, "poll-max-ns", "int",
iothread_get_poll_param,
iothread_set_poll_param,
NULL, &poll_max_ns_info, &error_abort);
object_class_property_add(klass, "poll-grow", "int",
iothread_get_poll_param,
iothread_set_poll_param,
NULL, &poll_grow_info, &error_abort);
object_class_property_add(klass, "poll-shrink", "int",
iothread_get_poll_param,
iothread_set_poll_param,
NULL, &poll_shrink_info, &error_abort);
}
static const TypeInfo iothread_info = {
.name = TYPE_IOTHREAD,
.parent = TYPE_OBJECT,
.class_init = iothread_class_init,
.instance_size = sizeof(IOThread),
.instance_init = iothread_instance_init,
.instance_finalize = iothread_instance_finalize,
.interfaces = (InterfaceInfo[]) {
{TYPE_USER_CREATABLE},
{}
},
};
static void iothread_register_types(void)
{
type_register_static(&iothread_info);
}
type_init(iothread_register_types)
char *iothread_get_id(IOThread *iothread)
{
return object_get_canonical_path_component(OBJECT(iothread));
}
AioContext *iothread_get_aio_context(IOThread *iothread)
{
return iothread->ctx;
}
static int query_one_iothread(Object *object, void *opaque)
{
IOThreadInfoList ***prev = opaque;
IOThreadInfoList *elem;
IOThreadInfo *info;
IOThread *iothread;
iothread = (IOThread *)object_dynamic_cast(object, TYPE_IOTHREAD);
if (!iothread) {
return 0;
}
info = g_new0(IOThreadInfo, 1);
info->id = iothread_get_id(iothread);
info->thread_id = iothread->thread_id;
info->poll_max_ns = iothread->poll_max_ns;
info->poll_grow = iothread->poll_grow;
info->poll_shrink = iothread->poll_shrink;
elem = g_new0(IOThreadInfoList, 1);
elem->value = info;
elem->next = NULL;
**prev = elem;
*prev = &elem->next;
return 0;
}
IOThreadInfoList *qmp_query_iothreads(Error **errp)
{
IOThreadInfoList *head = NULL;
IOThreadInfoList **prev = &head;
Object *container = object_get_objects_root();
object_child_foreach(container, query_one_iothread, &prev);
return head;
}
GMainContext *iothread_get_g_main_context(IOThread *iothread)
{
atomic_set(&iothread->run_gcontext, 1);
aio_notify(iothread->ctx);
return iothread->worker_context;
}
IOThread *iothread_create(const char *id, Error **errp)
{
Object *obj;
obj = object_new_with_props(TYPE_IOTHREAD,
object_get_internal_root(),
id, errp, NULL);
return IOTHREAD(obj);
}
void iothread_destroy(IOThread *iothread)
{
object_unparent(OBJECT(iothread));
}
/* Lookup IOThread by its id. Only finds user-created objects, not internal
* iothread_create() objects. */
IOThread *iothread_by_id(const char *id)
{
return IOTHREAD(object_resolve_path_type(id, TYPE_IOTHREAD, NULL));
}
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