[v4,3/6] iothread: add I/O thread object

This is a stand-in for Michael Roth's QContext.  I expect this to be
replaced once QContext is completed.

The IOThread object is an AioContext event loop thread.  This patch adds
the concept of multiple event loop threads, allowing users to define
them.

When SMP guests run on SMP hosts it makes sense to instantiate multiple
IOThreads.  This spreads event loop processing across multiple cores.
Note that additional patches are required to actually bind a device to
an IOThread.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 Makefile.objs             |   1 +
 include/sysemu/iothread.h |  30 +++++++++++
 iothread.c                | 123 ++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 154 insertions(+)
 create mode 100644 include/sysemu/iothread.h
 create mode 100644 iothread.c

On Fri, 21 Feb 2014 15:46:55 +0100
Stefan Hajnoczi <stefanha@redhat.com> wrote:

> This is a stand-in for Michael Roth's QContext.  I expect this to be
> replaced once QContext is completed.
> 
> The IOThread object is an AioContext event loop thread.  This patch adds
> the concept of multiple event loop threads, allowing users to define
> them.
> 
> When SMP guests run on SMP hosts it makes sense to instantiate multiple
> IOThreads.  This spreads event loop processing across multiple cores.
> Note that additional patches are required to actually bind a device to
> an IOThread.
> 
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  Makefile.objs             |   1 +
>  include/sysemu/iothread.h |  30 +++++++++++
>  iothread.c                | 123 ++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 154 insertions(+)
>  create mode 100644 include/sysemu/iothread.h
>  create mode 100644 iothread.c
> 
> diff --git a/Makefile.objs b/Makefile.objs
> index ac1d0e1..e24b89c 100644
> --- a/Makefile.objs
> +++ b/Makefile.objs
> @@ -42,6 +42,7 @@ libcacard-y += libcacard/vcardt.o
>  
>  ifeq ($(CONFIG_SOFTMMU),y)
>  common-obj-y = $(block-obj-y) blockdev.o blockdev-nbd.o block/
> +common-obj-y += iothread.o
>  common-obj-y += net/
>  common-obj-y += qdev-monitor.o device-hotplug.o
>  common-obj-$(CONFIG_WIN32) += os-win32.o
> diff --git a/include/sysemu/iothread.h b/include/sysemu/iothread.h
> new file mode 100644
> index 0000000..a32214a
> --- /dev/null
> +++ b/include/sysemu/iothread.h
> @@ -0,0 +1,30 @@
> +/*
> + * 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.
> + *
> + */
> +
> +#ifndef IOTHREAD_H
> +#define IOTHREAD_H
> +
> +#include "block/aio.h"
> +
> +#define TYPE_IOTHREAD "iothread"
> +
> +typedef struct IOThread IOThread;
> +
> +#define IOTHREAD(obj) \
> +   OBJECT_CHECK(IOThread, obj, TYPE_IOTHREAD)
> +
> +IOThread *iothread_find(const char *id);
> +char *iothread_get_id(IOThread *iothread);
> +AioContext *iothread_get_aio_context(IOThread *iothread);
> +
> +#endif /* IOTHREAD_H */
> diff --git a/iothread.c b/iothread.c
> new file mode 100644
> index 0000000..033de7f
> --- /dev/null
> +++ b/iothread.c
> @@ -0,0 +1,123 @@
> +/*
> + * 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 "qom/object.h"
> +#include "qom/object_interfaces.h"
> +#include "qemu/module.h"
> +#include "qemu/thread.h"
> +#include "block/aio.h"
> +#include "sysemu/iothread.h"
> +
> +#define IOTHREADS_PATH "/objects"
> +
> +typedef ObjectClass IOThreadClass;
> +struct IOThread {
> +    Object parent;
> +    QemuThread thread;
> +    AioContext *ctx;
> +    bool stopping;
> +};
> +
> +#define IOTHREAD_GET_CLASS(obj) \
> +   OBJECT_GET_CLASS(IOThreadClass, obj, TYPE_IOTHREAD)
> +#define IOTHREAD_CLASS(klass) \
> +   OBJECT_CLASS_CHECK(IOThreadClass, klass, TYPE_IOTHREAD)
> +
> +static void *iothread_run(void *opaque)
> +{
> +    IOThread *iothread = opaque;
> +
> +    while (!iothread->stopping) {
> +        aio_context_acquire(iothread->ctx);
> +        while (!iothread->stopping && aio_poll(iothread->ctx, true)) {
> +            /* Progress was made, keep going */
> +        }
> +        aio_context_release(iothread->ctx);
> +    }
> +    return NULL;
> +}
> +
> +static void iothread_instance_finalize(Object *obj)
> +{
> +    IOThread *iothread = IOTHREAD(obj);
> +
> +    iothread->stopping = true;
> +    aio_notify(iothread->ctx);
> +    qemu_thread_join(&iothread->thread);
> +    aio_context_unref(iothread->ctx);
> +}
> +
> +static void iothread_complete(UserCreatable *obj, Error **errp)
> +{
> +    IOThread *iothread = IOTHREAD(obj);
> +
> +    iothread->stopping = false;
> +    iothread->ctx = aio_context_new();
> +
> +    /* This assumes we are called from a thread with useful CPU affinity for us
> +     * to inherit.
> +     */
> +    qemu_thread_create(&iothread->thread, iothread_run,
> +                       iothread, QEMU_THREAD_JOINABLE);
> +}
> +
> +static void iothread_class_init(ObjectClass *klass, void *class_data)
> +{
> +    UserCreatableClass *ucc = USER_CREATABLE_CLASS(klass);
> +    ucc->complete = iothread_complete;
> +}
> +
> +static const TypeInfo iothread_info = {
> +    .name = TYPE_IOTHREAD,
> +    .parent = TYPE_OBJECT,
> +    .class_init = iothread_class_init,
> +    .instance_size = sizeof(IOThread),
> +    .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)
> +
> +IOThread *iothread_find(const char *id)
> +{
> +    Object *container = container_get(object_get_root(), IOTHREADS_PATH);
> +    Object *child;
> +
> +    child = object_property_get_link(container, id, NULL);
> +    if (!child) {
> +        return NULL;
> +    }
> +    return (IOThread *)object_dynamic_cast(child, TYPE_IOTHREAD);
> +}
> +
> +char *iothread_get_id(IOThread *iothread)
> +{
> +    /* The last path component is the identifier */
> +    char *path = object_get_canonical_path(OBJECT(iothread));
> +    char *id = g_strdup(&path[sizeof(IOTHREADS_PATH)]);
> +    g_free(path);
> +    return id;
> +}
it seems to be a more generic issue, i.e. QOM object wanting to know its
name. I've did something similar for memory_backend except of cutting
of parent's path.
Could we make and use a more generic accessor for object name?


> +AioContext *iothread_get_aio_context(IOThread *iothread)
> +{
> +    return iothread->ctx;
> +}

On Wed, Feb 26, 2014 at 11:00:19AM +0100, Igor Mammedov wrote:
> On Fri, 21 Feb 2014 15:46:55 +0100
> Stefan Hajnoczi <stefanha@redhat.com> wrote:
> > +char *iothread_get_id(IOThread *iothread)
> > +{
> > +    /* The last path component is the identifier */
> > +    char *path = object_get_canonical_path(OBJECT(iothread));
> > +    char *id = g_strdup(&path[sizeof(IOTHREADS_PATH)]);
> > +    g_free(path);
> > +    return id;
> > +}
> it seems to be a more generic issue, i.e. QOM object wanting to know its
> name. I've did something similar for memory_backend except of cutting
> of parent's path.
> Could we make and use a more generic accessor for object name?

Yes, I think we can do it in object.c.  Will send another revision.

Stefan