[Qemu-devel] Re: [PATCH V3 2/3] qemu: Generic asynchronous threading framework to offload tasks

[Corentin Chary]

On Thu, Jun 3, 2010 at 10:56 AM, Gautham R Shenoy <address@hidden> wrote:
> From: Aneesh Kumar K.V <address@hidden>
>
> This patch creates a generic asynchronous-task-offloading infrastructure. It's
> extracted out of the threading framework that is being used by paio.
>
> The reason for extracting out this generic infrastructure of the
> posix-aio-compat.c is so that other subsystems, such as virtio-9p could make 
> use
> of it for offloading tasks that could block.
>
> address@hidden: work_item_pool, async_work_init, async_work_release,
> async_cancel_work]
>
> Signed-off-by: Aneesh Kumar K.V <address@hidden>
> Signed-off-by: Gautham R Shenoy <address@hidden>
> ---
>  Makefile.objs |    3 +
>  async-work.c  |  136 
> +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  async-work.h  |   85 ++++++++++++++++++++++++++++++++++++
>  3 files changed, 223 insertions(+), 1 deletions(-)
>  create mode 100644 async-work.c
>  create mode 100644 async-work.h
>
> diff --git a/Makefile.objs b/Makefile.objs
> index ecdd53e..fd5ea4d 100644
> --- a/Makefile.objs
> +++ b/Makefile.objs
> @@ -9,6 +9,8 @@ qobject-obj-y += qerror.o
>
>  block-obj-y = cutils.o cache-utils.o qemu-malloc.o qemu-option.o module.o
>  block-obj-y += nbd.o block.o aio.o aes.o osdep.o qemu-config.o
> +block-obj-y += qemu-thread.o
> +block-obj-y += async-work.o
>  block-obj-$(CONFIG_POSIX) += posix-aio-compat.o
>  block-obj-$(CONFIG_LINUX_AIO) += linux-aio.o
>
> @@ -108,7 +110,6 @@ common-obj-y += iov.o
>  common-obj-$(CONFIG_VNC_TLS) += vnc-tls.o vnc-auth-vencrypt.o
>  common-obj-$(CONFIG_VNC_SASL) += vnc-auth-sasl.o
>  common-obj-$(CONFIG_COCOA) += cocoa.o
> -common-obj-$(CONFIG_IOTHREAD) += qemu-thread.o
>  common-obj-y += notify.o event_notifier.o
>  common-obj-y += qemu-timer.o
>
> diff --git a/async-work.c b/async-work.c
> new file mode 100644
> index 0000000..0675732
> --- /dev/null
> +++ b/async-work.c
> @@ -0,0 +1,136 @@
> +/*
> + * Async work support
> + *
> + * Copyright IBM, Corp. 2010
> + *
> + * Authors:
> + *  Aneesh Kumar K.V <address@hidden>
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2.  See
> + * the COPYING file in the top-level directory.
> + *
> + */
> +#include <stdio.h>
> +#include <errno.h>
> +#include <string.h>
> +#include <stdlib.h>
> +#include <signal.h>
> +#include "async-work.h"
> +#include "osdep.h"
> +
> +static void async_abort(int err, const char *what)
> +{
> +    fprintf(stderr, "%s failed: %s\n", what, strerror(err));
> +    abort();
> +}
> +
> +static void *async_worker_thread(void *data)
> +{
> +    struct async_queue *queue = data;
> +
> +    while (1) {
> +        struct work_item *work;
> +        int ret = 0;
> +        qemu_mutex_lock(&(queue->lock));
> +
> +        while (QTAILQ_EMPTY(&(queue->request_list)) &&
> +               (ret != ETIMEDOUT)) {
> +            ret = qemu_cond_timedwait(&(queue->cond),
> +                                        &(queue->lock), 10*100000);
> +        }
> +
> +        if (QTAILQ_EMPTY(&(queue->request_list)))
> +            goto check_exit;
> +
> +        work = QTAILQ_FIRST(&(queue->request_list));
> +        QTAILQ_REMOVE(&(queue->request_list), work, node);
> +        queue->idle_threads--;
> +        qemu_mutex_unlock(&(queue->lock));
> +
> +        /* execute the work function */
> +        work->func(work);

Here the queue is empty, but there is a job running. In the VNC server
I need to be able to "join" jobs (before resize, deconnection, etc..).
What do you thing about adding something like qemu_async_join(queue,
work) (if work is null, join all job) ?

> +        async_work_release(queue, work);
> +
> +        qemu_mutex_lock(&(queue->lock));
> +        queue->idle_threads++;
> +
> +check_exit:
> +        if ((queue->idle_threads > 0) &&
> +            (queue->cur_threads > queue->min_threads)) {
> +            /* we retain minimum number of threads */
> +            break;
> +        }
> +        qemu_mutex_unlock(&(queue->lock));
> +    }
> +
> +    queue->idle_threads--;
> +    queue->cur_threads--;
> +    qemu_mutex_unlock(&(queue->lock));
> +
> +    return NULL;
> +}
> +
> +static void spawn_async_thread(struct async_queue *queue)
> +{
> +    QemuThreadAttr attr;
> +    QemuThread thread;
> +    sigset_t set, oldset;
> +
> +    queue->cur_threads++;
> +    queue->idle_threads++;
> +
> +    qemu_thread_attr_init(&attr);
> +
> +    /* create a detached thread so that we don't need to wait on it */
> +    qemu_thread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
> +
> +    /* block all signals */
> +    if (sigfillset(&set)) {
> +        async_abort(errno, "sigfillset");
> +    }
> +
> +    if (sigprocmask(SIG_SETMASK, &set, &oldset)) {
> +        async_abort(errno, "sigprocmask");
> +    }
> +
> +    qemu_thread_create_attr(&thread, &attr, async_worker_thread, queue);
> +
> +    if (sigprocmask(SIG_SETMASK, &oldset, NULL)) {
> +        async_abort(errno, "sigprocmask restore");
> +    }

Using PTHREAD_CREATE_DETACHED and signal stuff here doesn't looks
really portable. Can't we abstract that into qemu-thread (then, we
just need port qemu-thread to windows) ?

> +}
> +
> +void qemu_async_submit(struct async_queue *queue, struct work_item *work)
> +{
> +    qemu_mutex_lock(&(queue->lock));
> +    if (queue->idle_threads == 0 && queue->cur_threads < queue->max_threads) 
> {
> +        spawn_async_thread(queue);
> +    }
> +    QTAILQ_INSERT_TAIL(&(queue->request_list), work, node);
> +    qemu_mutex_unlock(&(queue->lock));
> +    qemu_cond_signal(&(queue->cond));
> +}
> +
> +int qemu_async_cancel_work(struct async_queue *queue, struct work_item *work)
> +{
> +    struct work_item *ret_work;
> +    int found = 0;
> +
> +    qemu_mutex_lock(&(queue->lock));
> +    QTAILQ_FOREACH(ret_work, &(queue->request_list), node) {
> +        if (ret_work == work) {
> +            QTAILQ_REMOVE(&(queue->request_list), ret_work, node);
> +            found = 1;
> +            break;
> +        }
> +    }
> +    qemu_mutex_unlock(&(queue->lock));
> +
> +    if (found) {
> +        async_work_release(queue, work);
> +        return 0;
> +    }
> +
> +    return 1;
> +}
> +
> diff --git a/async-work.h b/async-work.h
> new file mode 100644
> index 0000000..8389f56
> --- /dev/null
> +++ b/async-work.h
> @@ -0,0 +1,85 @@
> +/*
> + * Async work support
> + *
> + * Copyright IBM, Corp. 2010
> + *
> + * Authors:
> + *  Aneesh Kumar K.V <address@hidden>
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2.  See
> + * the COPYING file in the top-level directory.
> + *
> + */
> +#ifndef QEMU_ASYNC_WORK_H
> +#define QEMU_ASYNC_WORK_H
> +
> +#include "qemu-queue.h"
> +#include "qemu-common.h"
> +#include "qemu-thread.h"
> +
> +struct async_queue
> +{
> +    QemuMutex lock;
> +    QemuCond cond;
> +    int max_threads;
> +    int min_threads;
> +    int cur_threads;
> +    int idle_threads;
> +    QTAILQ_HEAD(, work_item) request_list;
> +    QTAILQ_HEAD(, work_item) work_item_pool;
> +};
> +
> +struct work_item
> +{
> +    QTAILQ_ENTRY(work_item) node;
> +    void (*func)(struct work_item *work);
> +    void *private;
> +};
> +
> +static inline void async_queue_init(struct async_queue *queue,
> +                                   int max_threads, int min_threads)
> +{
> +    queue->cur_threads  = 0;
> +    queue->idle_threads = 0;
> +    queue->max_threads  = max_threads;
> +    queue->min_threads  = min_threads;
> +    QTAILQ_INIT(&(queue->request_list));
> +    QTAILQ_INIT(&(queue->work_item_pool));
> +    qemu_mutex_init(&(queue->lock));
> +    qemu_cond_init(&(queue->cond));
> +}
> +
> +static inline struct work_item *async_work_init(struct async_queue *queue,
> +                                  void (*func)(struct work_item *),
> +                                  void *data)
> +{
> +    struct work_item *work;
> +    qemu_mutex_lock(&(queue->lock));
> +    if (QTAILQ_EMPTY(&(queue->work_item_pool))) {
> +        work = qemu_mallocz(sizeof(*work));
> +    } else {
> +        work = QTAILQ_FIRST(&(queue->work_item_pool));
> +        QTAILQ_REMOVE(&(queue->work_item_pool), work, node);
> +    }
> +
> +    work->func  = func;
> +    work->private  = data;
> +    qemu_mutex_unlock(&(queue->lock));
> +
> +    return work;
> +}
> +
> +static inline void async_work_release(struct async_queue *queue,
> +                                        struct work_item *work)
> +{
> +    qemu_mutex_lock(&(queue->lock));
> +    QTAILQ_INSERT_TAIL(&(queue->work_item_pool), work, node);
> +    qemu_mutex_unlock(&(queue->lock));
> +}
> +
> +extern void qemu_async_submit(struct async_queue *queue,
> +                                 struct work_item *work);
> +
> +extern int qemu_async_cancel_work(struct async_queue *queue,
> +                    struct work_item *work);
> +#endif
>
>



-- 
Corentin Chary
http://xf.iksaif.net