[Qemu-devel] [RFC 3/7] iothread: add I/O thread object

[Stefan Hajnoczi]

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 <address@hidden>
---
 Makefile.objs             |   1 +
 include/sysemu/iothread.h |  31 +++++++++++++
 iothread.c                | 115 ++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 147 insertions(+)
 create mode 100644 include/sysemu/iothread.h
 create mode 100644 iothread.c

diff --git a/Makefile.objs b/Makefile.objs
index 2b6c1fe..a1102a5 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 += readline.o
 common-obj-y += qdev-monitor.o device-hotplug.o
diff --git a/include/sysemu/iothread.h b/include/sysemu/iothread.h
new file mode 100644
index 0000000..8c49bd6
--- /dev/null
+++ b/include/sysemu/iothread.h
@@ -0,0 +1,31 @@
+/*
+ * Event loop thread
+ *
+ * Copyright Red Hat Inc., 2013
+ *
+ * Authors:
+ *  Stefan Hajnoczi   <address@hidden>
+ *
+ * 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"
+#define IOTHREADS_PATH "/backends/iothreads"
+
+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..dbc6047
--- /dev/null
+++ b/iothread.c
@@ -0,0 +1,115 @@
+/*
+ * Event loop thread
+ *
+ * Copyright Red Hat Inc., 2013
+ *
+ * Authors:
+ *  Stefan Hajnoczi   <address@hidden>
+ *
+ * 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 "qemu/module.h"
+#include "qemu/thread.h"
+#include "block/aio.h"
+#include "sysemu/iothread.h"
+
+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;
+
+    for (;;) {
+        /* TODO can we optimize away acquire/release to only happen when
+         * aio_notify() was called?
+         */
+        aio_context_acquire(iothread->ctx);
+        if (iothread->stopping) {
+            aio_context_release(iothread->ctx);
+            break;
+        }
+        aio_poll(iothread->ctx, true);
+        aio_context_release(iothread->ctx);
+    }
+    return NULL;
+}
+
+static void iothread_instance_init(Object *obj)
+{
+    IOThread *iothread = IOTHREAD(obj);
+
+    iothread->stopping = false;
+    iothread->ctx = aio_context_new();
+
+    /* This assumes .instance_init() is 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_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 const TypeInfo iothread_info = {
+    .name = TYPE_IOTHREAD,
+    .parent = TYPE_OBJECT,
+    .instance_size = sizeof(IOThread),
+    .instance_init = iothread_instance_init,
+    .instance_finalize = iothread_instance_finalize,
+};
+
+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(child);
+}
+
+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;
+}
+
+AioContext *iothread_get_aio_context(IOThread *iothread)
+{
+    return iothread->ctx;
+}
-- 
1.8.4.2