virtio-balloon: optimize the virtio-balloon on the ARM platform

Optimize the virtio-balloon feature on the ARM platform by adding
a variable to keep track of the current hot-plugged pc-dimm size,
instead of traversing the virtual machine's memory modules to count
the current RAM size during the balloon inflation or deflation
process. This variable can be updated only when plugging or unplugging
the device, which will result in an increase of approximately 60%
efficiency of balloon process on the ARM platform.

We tested the total amount of time required for the balloon inflation process on ARM:
inflate the balloon to 64GB of a 128GB guest under stress.
Before: 102 seconds
After: 42 seconds

Signed-off-by: Qi Xi <xiqi2@huawei.com>
Signed-off-by: Ming Yang yangming73@huawei.com
Message-Id: <e13bc78f96774bfab4576814c293aa52@huawei.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: David Hildenbrand <david@redhat.com>

1 files changed, 5 insertions, 28 deletions

diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
index 746f07c..2814a47 100644
--- a/hw/virtio/virtio-balloon.c
+++ b/hw/virtio/virtio-balloon.c
@@ -729,37 +729,14 @@ static void virtio_balloon_get_config(VirtIODevice *vdev, uint8_t *config_data)
     memcpy(config_data, &config, virtio_balloon_config_size(dev));
 }
 
-static int build_dimm_list(Object *obj, void *opaque)
-{
-    GSList **list = opaque;
-
-    if (object_dynamic_cast(obj, TYPE_PC_DIMM)) {
-        DeviceState *dev = DEVICE(obj);
-        if (dev->realized) { /* only realized DIMMs matter */
-            *list = g_slist_prepend(*list, dev);
-        }
-    }
-
-    object_child_foreach(obj, build_dimm_list, opaque);
-    return 0;
-}
-
 static ram_addr_t get_current_ram_size(void)
 {
-    GSList *list = NULL, *item;
-    ram_addr_t size = current_machine->ram_size;
-
-    build_dimm_list(qdev_get_machine(), &list);
-    for (item = list; item; item = g_slist_next(item)) {
-        Object *obj = OBJECT(item->data);
-        if (!strcmp(object_get_typename(obj), TYPE_PC_DIMM)) {
-            size += object_property_get_int(obj, PC_DIMM_SIZE_PROP,
-                                            &error_abort);
-        }
+    MachineState *machine = MACHINE(qdev_get_machine());
+    if (machine->device_memory) {
+        return machine->ram_size + machine->device_memory->dimm_size;
+    } else {
+        return machine->ram_size;
     }
-    g_slist_free(list);
-
-    return size;
 }
 
 static bool virtio_balloon_page_poison_support(void *opaque)