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aio: add generic thread-pool facility

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Add a generic thread-pool.  The code is roughly based on posix-aio-compat.c,
with some changes, especially the following:

- use QemuSemaphore instead of QemuCond;

- separate the state of the thread from the return code of the worker
function.  The return code is totally opaque for the thread pool;

- do not busy wait when doing cancellation.

A more generic threadpool (but still specific to I/O so that in the future
it can use special scheduling classes or PI mutexes) can have many uses:
it allows more flexibility in raw-posix.c and can more easily be extended
to Win32, and it will also be used to do an msync of the persistent bitmap.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2012-02-23 13:23:34 +01:00
parent 38b14db34e
commit d354c7eccf
4 changed files with 322 additions and 1 deletions
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2
Makefile.objs
View file

@ -43,7 +43,7 @@ coroutine-obj-$(CONFIG_WIN32) += coroutine-win32.o
block-obj-y = iov.o cache-utils.o qemu-option.o module.o async.o
block-obj-y += nbd.o block.o blockjob.o aes.o qemu-config.o
block-obj-y += qemu-progress.o qemu-sockets.o uri.o notify.o
block-obj-y += thread-pool.o qemu-progress.o qemu-sockets.o uri.o notify.o
block-obj-y += $(coroutine-obj-y) $(qobject-obj-y) $(version-obj-y)
block-obj-$(CONFIG_POSIX) += posix-aio-compat.o
block-obj-$(CONFIG_POSIX) += event_notifier-posix.o aio-posix.o

282
thread-pool.c Normal file
View file

@ -0,0 +1,282 @@
/*
* 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 "osdep.h"
#include "qemu-coroutine.h"
#include "trace.h"
#include "block_int.h"
#include "event_notifier.h"
#include "thread-pool.h"
static void do_spawn_thread(void);
typedef struct ThreadPoolElement ThreadPoolElement;
enum ThreadState {
THREAD_QUEUED,
THREAD_ACTIVE,
THREAD_DONE,
THREAD_CANCELED,
};
struct ThreadPoolElement {
BlockDriverAIOCB common;
ThreadPoolFunc *func;
void *arg;
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;
};
static EventNotifier notifier;
static QemuMutex lock;
static QemuCond check_cancel;
static QemuSemaphore sem;
static int max_threads = 64;
static QEMUBH *new_thread_bh;
/* The following variables are protected by the global mutex. */
static QLIST_HEAD(, ThreadPoolElement) head;
/* The following variables are protected by lock. */
static QTAILQ_HEAD(, ThreadPoolElement) request_list;
static int cur_threads;
static int idle_threads;
static int new_threads; /* backlog of threads we need to create */
static int pending_threads; /* threads created but not running yet */
static int pending_cancellations; /* whether we need a cond_broadcast */
static void *worker_thread(void *unused)
{
qemu_mutex_lock(&lock);
pending_threads--;
do_spawn_thread();
while (1) {
ThreadPoolElement *req;
int ret;
do {
idle_threads++;
qemu_mutex_unlock(&lock);
ret = qemu_sem_timedwait(&sem, 10000);
qemu_mutex_lock(&lock);
idle_threads--;
} while (ret == -1 && !QTAILQ_EMPTY(&request_list));
if (ret == -1) {
break;
}
req = QTAILQ_FIRST(&request_list);
QTAILQ_REMOVE(&request_list, req, reqs);
req->state = THREAD_ACTIVE;
qemu_mutex_unlock(&lock);
ret = req->func(req->arg);
qemu_mutex_lock(&lock);
req->state = THREAD_DONE;
req->ret = ret;
if (pending_cancellations) {
qemu_cond_broadcast(&check_cancel);
}
event_notifier_set(&notifier);
}
cur_threads--;
qemu_mutex_unlock(&lock);
return NULL;
}
static void do_spawn_thread(void)
{
QemuThread t;
/* Runs with lock taken. */
if (!new_threads) {
return;
}
new_threads--;
pending_threads++;
qemu_thread_create(&t, worker_thread, NULL, QEMU_THREAD_DETACHED);
}
static void spawn_thread_bh_fn(void *opaque)
{
qemu_mutex_lock(&lock);
do_spawn_thread();
qemu_mutex_unlock(&lock);
}
static void spawn_thread(void)
{
cur_threads++;
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 (!pending_threads) {
qemu_bh_schedule(new_thread_bh);
}
}
static void event_notifier_ready(EventNotifier *notifier)
{
ThreadPoolElement *elem, *next;
event_notifier_test_and_clear(notifier);
restart:
QLIST_FOREACH_SAFE(elem, &head, all, next) {
if (elem->state != THREAD_CANCELED && elem->state != THREAD_DONE) {
continue;
}
if (elem->state == THREAD_DONE) {
trace_thread_pool_complete(elem, elem->common.opaque, elem->ret);
}
if (elem->state == THREAD_DONE && elem->common.cb) {
qemu_mutex_lock(&lock);
int ret = elem->ret;
qemu_mutex_unlock(&lock);
QLIST_REMOVE(elem, all);
elem->common.cb(elem->common.opaque, ret);
qemu_aio_release(elem);
goto restart;
} else {
/* remove the request */
QLIST_REMOVE(elem, all);
qemu_aio_release(elem);
}
}
}
static int thread_pool_active(EventNotifier *notifier)
{
return !QLIST_EMPTY(&head);
}
static void thread_pool_cancel(BlockDriverAIOCB *acb)
{
ThreadPoolElement *elem = (ThreadPoolElement *)acb;
trace_thread_pool_cancel(elem, elem->common.opaque);
qemu_mutex_lock(&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(&sem, 0) == 0) {
QTAILQ_REMOVE(&request_list, elem, reqs);
elem->state = THREAD_CANCELED;
event_notifier_set(&notifier);
} else {
pending_cancellations++;
while (elem->state != THREAD_CANCELED && elem->state != THREAD_DONE) {
qemu_cond_wait(&check_cancel, &lock);
}
pending_cancellations--;
}
qemu_mutex_unlock(&lock);
}
static AIOPool thread_pool_cb_pool = {
.aiocb_size = sizeof(ThreadPoolElement),
.cancel = thread_pool_cancel,
};
BlockDriverAIOCB *thread_pool_submit_aio(ThreadPoolFunc *func, void *arg,
BlockDriverCompletionFunc *cb, void *opaque)
{
ThreadPoolElement *req;
req = qemu_aio_get(&thread_pool_cb_pool, NULL, cb, opaque);
req->func = func;
req->arg = arg;
req->state = THREAD_QUEUED;
QLIST_INSERT_HEAD(&head, req, all);
trace_thread_pool_submit(req, arg);
qemu_mutex_lock(&lock);
if (idle_threads == 0 && cur_threads < max_threads) {
spawn_thread();
}
QTAILQ_INSERT_TAIL(&request_list, req, reqs);
qemu_mutex_unlock(&lock);
qemu_sem_post(&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(ThreadPoolFunc *func, void *arg)
{
ThreadPoolCo tpc = { .co = qemu_coroutine_self(), .ret = -EINPROGRESS };
assert(qemu_in_coroutine());
thread_pool_submit_aio(func, arg, thread_pool_co_cb, &tpc);
qemu_coroutine_yield();
return tpc.ret;
}
void thread_pool_submit(ThreadPoolFunc *func, void *arg)
{
thread_pool_submit_aio(func, arg, NULL, NULL);
}
static void thread_pool_init(void)
{
QLIST_INIT(&head);
event_notifier_init(&notifier, false);
qemu_mutex_init(&lock);
qemu_cond_init(&check_cancel);
qemu_sem_init(&sem, 0);
qemu_aio_set_event_notifier(&notifier, event_notifier_ready,
thread_pool_active);
QTAILQ_INIT(&request_list);
new_thread_bh = qemu_bh_new(spawn_thread_bh_fn, NULL);
}
block_init(thread_pool_init)

34
thread-pool.h Normal file
View file

@ -0,0 +1,34 @@
/*
* 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.
*/
#ifndef QEMU_THREAD_POOL_H
#define QEMU_THREAD_POOL_H 1
#include "qemu-common.h"
#include "qemu-queue.h"
#include "qemu-thread.h"
#include "qemu-coroutine.h"
#include "block_int.h"
typedef int ThreadPoolFunc(void *opaque);
BlockDriverAIOCB *thread_pool_submit_aio(ThreadPoolFunc *func, void *arg,
BlockDriverCompletionFunc *cb, void *opaque);
int coroutine_fn thread_pool_submit_co(ThreadPoolFunc *func, void *arg);
void thread_pool_submit(ThreadPoolFunc *func, void *arg);
#endif

5
trace-events
View file

@ -90,6 +90,11 @@ virtio_blk_rw_complete(void *req, int ret) "req %p ret %d"
virtio_blk_handle_write(void *req, uint64_t sector, size_t nsectors) "req %p sector %"PRIu64" nsectors %zu"
virtio_blk_handle_read(void *req, uint64_t sector, size_t nsectors) "req %p sector %"PRIu64" nsectors %zu"
# thread-pool.c
thread_pool_submit(void *req, void *opaque) "req %p opaque %p"
thread_pool_complete(void *req, void *opaque, int ret) "req %p opaque %p ret %d"
thread_pool_cancel(void *req, void *opaque) "req %p opaque %p"
# posix-aio-compat.c
paio_submit(void *acb, void *opaque, int64_t sector_num, int nb_sectors, int type) "acb %p opaque %p sector_num %"PRId64" nb_sectors %d type %d"
paio_complete(void *acb, void *opaque, int ret) "acb %p opaque %p ret %d"