/*
* 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/osdep.h"
#include "qemu/queue.h"
#include "qemu/thread.h"
#include "qemu/coroutine.h"
#include "trace.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,
};
struct ThreadPoolElement {
BlockAIOCB 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 {
AioContext *ctx;
QEMUBH *completion_bh;
QemuMutex lock;
QemuCond worker_stopped;
QemuCond request_cond;
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 min_threads;
int max_threads;
};
static void *worker_thread(void *opaque)
{
ThreadPool *pool = opaque;
qemu_mutex_lock(&pool->lock);
pool->pending_threads--;
do_spawn_thread(pool);
while (pool->cur_threads <= pool->max_threads) {
ThreadPoolElement *req;
int ret;
if (QTAILQ_EMPTY(&pool->request_list)) {
pool->idle_threads++;
ret = qemu_cond_timedwait(&pool->request_cond, &pool->lock, 10000);
pool->idle_threads--;
if (ret == 0 &&
QTAILQ_EMPTY(&pool->request_list) &&
pool->cur_threads > pool->min_threads) {
/* Timed out + no work to do + no need for warm threads = exit. */
break;
}
/*
* Even if there was some work to do, check if there aren't
* too many worker threads before picking it up.
*/
continue;
}
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_bh_schedule(pool->completion_bh);
qemu_mutex_lock(&pool->lock);
}
pool->cur_threads--;
qemu_cond_signal(&pool->worker_stopped);
qemu_mutex_unlock(&pool->lock);
/*
* Wake up another thread, in case we got a wakeup but decided
* to exit due to pool->cur_threads > pool->max_threads.
*/
qemu_cond_signal(&pool->request_cond);
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", 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 thread_pool_completion_bh(void *opaque)
{
ThreadPool *pool = opaque;
ThreadPoolElement *elem, *next;
aio_context_acquire(pool->ctx);
restart:
QLIST_FOREACH_SAFE(elem, &pool->head, all, next) {
if (elem->state != THREAD_DONE) {
continue;
}
trace_thread_pool_complete(pool, elem, elem->common.opaque,
elem->ret);
QLIST_REMOVE(elem, all);
if (elem->common.cb) {
/* Read state before ret. */
smp_rmb();
/* Schedule ourselves in case elem->common.cb() calls aio_poll() to
* wait for another request that completed at the same time.
*/
qemu_bh_schedule(pool->completion_bh);
aio_context_release(pool->ctx);
elem->common.cb(elem->common.opaque, elem->ret);
aio_context_acquire(pool->ctx);
/* We can safely cancel the completion_bh here regardless of someone
* else having scheduled it meanwhile because we reenter the
* completion function anyway (goto restart).
*/
qemu_bh_cancel(pool->completion_bh);
qemu_aio_unref(elem);
goto restart;
} else {
qemu_aio_unref(elem);
}
}
aio_context_release(pool->ctx);
}
static void thread_pool_cancel(BlockAIOCB *acb)
{
ThreadPoolElement *elem = (ThreadPoolElement *)acb;
ThreadPool *pool = elem->pool;
trace_thread_pool_cancel(elem, elem->common.opaque);
QEMU_LOCK_GUARD(&pool->lock);
if (elem->state == THREAD_QUEUED) {
QTAILQ_REMOVE(&pool->request_list, elem, reqs);
qemu_bh_schedule(pool->completion_bh);
elem->state = THREAD_DONE;
elem->ret = -ECANCELED;
}
}
static AioContext *thread_pool_get_aio_context(BlockAIOCB *acb)
{
ThreadPoolElement *elem = (ThreadPoolElement *)acb;
ThreadPool *pool = elem->pool;
return pool->ctx;
}
static const AIOCBInfo thread_pool_aiocb_info = {
.aiocb_size = sizeof(ThreadPoolElement),
.cancel_async = thread_pool_cancel,
.get_aio_context = thread_pool_get_aio_context,
};
BlockAIOCB *thread_pool_submit_aio(ThreadPool *pool,
ThreadPoolFunc *func, void *arg,
BlockCompletionFunc *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_cond_signal(&pool->request_cond);
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;
aio_co_wake(co->co);
}
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);
}
void thread_pool_update_params(ThreadPool *pool, AioContext *ctx)
{
qemu_mutex_lock(&pool->lock);
pool->min_threads = ctx->thread_pool_min;
pool->max_threads = ctx->thread_pool_max;
/*
* We either have to:
* - Increase the number available of threads until over the min_threads
* threshold.
* - Bump the worker threads so that they exit, until under the max_threads
* threshold.
* - Do nothing. The current number of threads fall in between the min and
* max thresholds. We'll let the pool manage itself.
*/
for (int i = pool->cur_threads; i < pool->min_threads; i++) {
spawn_thread(pool);
}
for (int i = pool->cur_threads; i > pool->max_threads; i--) {
qemu_cond_signal(&pool->request_cond);
}
qemu_mutex_unlock(&pool->lock);
}
static void thread_pool_init_one(ThreadPool *pool, AioContext *ctx)
{
if (!ctx) {
ctx = qemu_get_aio_context();
}
memset(pool, 0, sizeof(*pool));
pool->ctx = ctx;
pool->completion_bh = aio_bh_new(ctx, thread_pool_completion_bh, pool);
qemu_mutex_init(&pool->lock);
qemu_cond_init(&pool->worker_stopped);
qemu_cond_init(&pool->request_cond);
pool->new_thread_bh = aio_bh_new(ctx, spawn_thread_bh_fn, pool);
QLIST_INIT(&pool->head);
QTAILQ_INIT(&pool->request_list);
thread_pool_update_params(pool, ctx);
}
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->max_threads = 0;
qemu_cond_broadcast(&pool->request_cond);
while (pool->cur_threads > 0) {
qemu_cond_wait(&pool->worker_stopped, &pool->lock);
}
qemu_mutex_unlock(&pool->lock);
qemu_bh_delete(pool->completion_bh);
qemu_cond_destroy(&pool->request_cond);
qemu_cond_destroy(&pool->worker_stopped);
qemu_mutex_destroy(&pool->lock);
g_free(pool);
}
