Skip to content

HTTPS clone URL

Subversion checkout URL

You can clone with HTTPS or Subversion.

Download ZIP
Fetching contributors…

Cannot retrieve contributors at this time

349 lines (293 sloc) 9.77 kb
/*
* QEMU block layer thread pool
*
* Copyright IBM, Corp. 2008
* Copyright Red Hat, Inc. 2012
*
* Authors:
* Anthony Liguori <aliguori@us.ibm.com>
* Paolo Bonzini <pbonzini@redhat.com>
*
* This work is licensed under the terms of the GNU GPL, version 2. See
* the COPYING file in the top-level directory.
*
* Contributions after 2012-01-13 are licensed under the terms of the
* GNU GPL, version 2 or (at your option) any later version.
*/
#include "qemu-common.h"
#include "qemu/queue.h"
#include "qemu/thread.h"
#include "qemu/osdep.h"
#include "block/coroutine.h"
#include "trace.h"
#include "block/block_int.h"
#include "qemu/event_notifier.h"
#include "block/thread-pool.h"
#include "qemu/main-loop.h"
static void do_spawn_thread(ThreadPool *pool);
typedef struct ThreadPoolElement ThreadPoolElement;
enum ThreadState {
THREAD_QUEUED,
THREAD_ACTIVE,
THREAD_DONE,
THREAD_CANCELED,
};
struct ThreadPoolElement {
BlockDriverAIOCB common;
ThreadPool *pool;
ThreadPoolFunc *func;
void *arg;
/* Moving state out of THREAD_QUEUED is protected by lock. After
* that, only the worker thread can write to it. Reads and writes
* of state and ret are ordered with memory barriers.
*/
enum ThreadState state;
int ret;
/* Access to this list is protected by lock. */
QTAILQ_ENTRY(ThreadPoolElement) reqs;
/* Access to this list is protected by the global mutex. */
QLIST_ENTRY(ThreadPoolElement) all;
};
struct ThreadPool {
EventNotifier notifier;
AioContext *ctx;
QemuMutex lock;
QemuCond check_cancel;
QemuCond worker_stopped;
QemuSemaphore sem;
int max_threads;
QEMUBH *new_thread_bh;
/* The following variables are only accessed from one AioContext. */
QLIST_HEAD(, ThreadPoolElement) head;
/* The following variables are protected by lock. */
QTAILQ_HEAD(, ThreadPoolElement) request_list;
int cur_threads;
int idle_threads;
int new_threads; /* backlog of threads we need to create */
int pending_threads; /* threads created but not running yet */
int pending_cancellations; /* whether we need a cond_broadcast */
bool stopping;
};
static void *worker_thread(void *opaque)
{
ThreadPool *pool = opaque;
qemu_mutex_lock(&pool->lock);
pool->pending_threads--;
do_spawn_thread(pool);
while (!pool->stopping) {
ThreadPoolElement *req;
int ret;
do {
pool->idle_threads++;
qemu_mutex_unlock(&pool->lock);
ret = qemu_sem_timedwait(&pool->sem, 10000);
qemu_mutex_lock(&pool->lock);
pool->idle_threads--;
} while (ret == -1 && !QTAILQ_EMPTY(&pool->request_list));
if (ret == -1 || pool->stopping) {
break;
}
req = QTAILQ_FIRST(&pool->request_list);
QTAILQ_REMOVE(&pool->request_list, req, reqs);
req->state = THREAD_ACTIVE;
qemu_mutex_unlock(&pool->lock);
ret = req->func(req->arg);
req->ret = ret;
/* Write ret before state. */
smp_wmb();
req->state = THREAD_DONE;
qemu_mutex_lock(&pool->lock);
if (pool->pending_cancellations) {
qemu_cond_broadcast(&pool->check_cancel);
}
event_notifier_set(&pool->notifier);
}
pool->cur_threads--;
qemu_cond_signal(&pool->worker_stopped);
qemu_mutex_unlock(&pool->lock);
return NULL;
}
static void do_spawn_thread(ThreadPool *pool)
{
QemuThread t;
/* Runs with lock taken. */
if (!pool->new_threads) {
return;
}
pool->new_threads--;
pool->pending_threads++;
qemu_thread_create(&t, worker_thread, pool, QEMU_THREAD_DETACHED);
}
static void spawn_thread_bh_fn(void *opaque)
{
ThreadPool *pool = opaque;
qemu_mutex_lock(&pool->lock);
do_spawn_thread(pool);
qemu_mutex_unlock(&pool->lock);
}
static void spawn_thread(ThreadPool *pool)
{
pool->cur_threads++;
pool->new_threads++;
/* If there are threads being created, they will spawn new workers, so
* we don't spend time creating many threads in a loop holding a mutex or
* starving the current vcpu.
*
* If there are no idle threads, ask the main thread to create one, so we
* inherit the correct affinity instead of the vcpu affinity.
*/
if (!pool->pending_threads) {
qemu_bh_schedule(pool->new_thread_bh);
}
}
static void event_notifier_ready(EventNotifier *notifier)
{
ThreadPool *pool = container_of(notifier, ThreadPool, notifier);
ThreadPoolElement *elem, *next;
event_notifier_test_and_clear(notifier);
restart:
QLIST_FOREACH_SAFE(elem, &pool->head, all, next) {
if (elem->state != THREAD_CANCELED && elem->state != THREAD_DONE) {
continue;
}
if (elem->state == THREAD_DONE) {
trace_thread_pool_complete(pool, elem, elem->common.opaque,
elem->ret);
}
if (elem->state == THREAD_DONE && elem->common.cb) {
QLIST_REMOVE(elem, all);
/* Read state before ret. */
smp_rmb();
elem->common.cb(elem->common.opaque, elem->ret);
qemu_aio_release(elem);
goto restart;
} else {
/* remove the request */
QLIST_REMOVE(elem, all);
qemu_aio_release(elem);
}
}
}
static void thread_pool_cancel(BlockDriverAIOCB *acb)
{
ThreadPoolElement *elem = (ThreadPoolElement *)acb;
ThreadPool *pool = elem->pool;
trace_thread_pool_cancel(elem, elem->common.opaque);
qemu_mutex_lock(&pool->lock);
if (elem->state == THREAD_QUEUED &&
/* No thread has yet started working on elem. we can try to "steal"
* the item from the worker if we can get a signal from the
* semaphore. Because this is non-blocking, we can do it with
* the lock taken and ensure that elem will remain THREAD_QUEUED.
*/
qemu_sem_timedwait(&pool->sem, 0) == 0) {
QTAILQ_REMOVE(&pool->request_list, elem, reqs);
elem->state = THREAD_CANCELED;
event_notifier_set(&pool->notifier);
} else {
pool->pending_cancellations++;
while (elem->state != THREAD_CANCELED && elem->state != THREAD_DONE) {
qemu_cond_wait(&pool->check_cancel, &pool->lock);
}
pool->pending_cancellations--;
}
qemu_mutex_unlock(&pool->lock);
}
static const AIOCBInfo thread_pool_aiocb_info = {
.aiocb_size = sizeof(ThreadPoolElement),
.cancel = thread_pool_cancel,
};
BlockDriverAIOCB *thread_pool_submit_aio(ThreadPool *pool,
ThreadPoolFunc *func, void *arg,
BlockDriverCompletionFunc *cb, void *opaque)
{
ThreadPoolElement *req;
req = qemu_aio_get(&thread_pool_aiocb_info, NULL, cb, opaque);
req->func = func;
req->arg = arg;
req->state = THREAD_QUEUED;
req->pool = pool;
QLIST_INSERT_HEAD(&pool->head, req, all);
trace_thread_pool_submit(pool, req, arg);
qemu_mutex_lock(&pool->lock);
if (pool->idle_threads == 0 && pool->cur_threads < pool->max_threads) {
spawn_thread(pool);
}
QTAILQ_INSERT_TAIL(&pool->request_list, req, reqs);
qemu_mutex_unlock(&pool->lock);
qemu_sem_post(&pool->sem);
return &req->common;
}
typedef struct ThreadPoolCo {
Coroutine *co;
int ret;
} ThreadPoolCo;
static void thread_pool_co_cb(void *opaque, int ret)
{
ThreadPoolCo *co = opaque;
co->ret = ret;
qemu_coroutine_enter(co->co, NULL);
}
int coroutine_fn thread_pool_submit_co(ThreadPool *pool, ThreadPoolFunc *func,
void *arg)
{
ThreadPoolCo tpc = { .co = qemu_coroutine_self(), .ret = -EINPROGRESS };
assert(qemu_in_coroutine());
thread_pool_submit_aio(pool, func, arg, thread_pool_co_cb, &tpc);
qemu_coroutine_yield();
return tpc.ret;
}
void thread_pool_submit(ThreadPool *pool, ThreadPoolFunc *func, void *arg)
{
thread_pool_submit_aio(pool, func, arg, NULL, NULL);
}
static void thread_pool_init_one(ThreadPool *pool, AioContext *ctx)
{
if (!ctx) {
ctx = qemu_get_aio_context();
}
memset(pool, 0, sizeof(*pool));
event_notifier_init(&pool->notifier, false);
pool->ctx = ctx;
qemu_mutex_init(&pool->lock);
qemu_cond_init(&pool->check_cancel);
qemu_cond_init(&pool->worker_stopped);
qemu_sem_init(&pool->sem, 0);
pool->max_threads = 64;
pool->new_thread_bh = aio_bh_new(ctx, spawn_thread_bh_fn, pool);
QLIST_INIT(&pool->head);
QTAILQ_INIT(&pool->request_list);
aio_set_event_notifier(ctx, &pool->notifier, event_notifier_ready);
}
ThreadPool *thread_pool_new(AioContext *ctx)
{
ThreadPool *pool = g_new(ThreadPool, 1);
thread_pool_init_one(pool, ctx);
return pool;
}
void thread_pool_free(ThreadPool *pool)
{
if (!pool) {
return;
}
assert(QLIST_EMPTY(&pool->head));
qemu_mutex_lock(&pool->lock);
/* Stop new threads from spawning */
qemu_bh_delete(pool->new_thread_bh);
pool->cur_threads -= pool->new_threads;
pool->new_threads = 0;
/* Wait for worker threads to terminate */
pool->stopping = true;
while (pool->cur_threads > 0) {
qemu_sem_post(&pool->sem);
qemu_cond_wait(&pool->worker_stopped, &pool->lock);
}
qemu_mutex_unlock(&pool->lock);
aio_set_event_notifier(pool->ctx, &pool->notifier, NULL);
qemu_sem_destroy(&pool->sem);
qemu_cond_destroy(&pool->check_cancel);
qemu_cond_destroy(&pool->worker_stopped);
qemu_mutex_destroy(&pool->lock);
event_notifier_cleanup(&pool->notifier);
g_free(pool);
}
Jump to Line
Something went wrong with that request. Please try again.