[PATCH] virtio-balloon: optimize the virtio-balloon on the ARM platform.

[Yangming]

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 more 
than 60% efficiency of balloon process on the ARM platform.

Signed-off-by: Qi Xi <xiqi2@huawei.com>
Signed-off-by: Ming Yang yangming73@huawei.com
---
 hw/mem/pc-dimm.c           |  2 ++
 hw/virtio/virtio-balloon.c | 44 +++++++++++++-------------------------
 include/hw/boards.h        |  1 +
 3 files changed, 18 insertions(+), 29 deletions(-)

diff --git a/hw/mem/pc-dimm.c b/hw/mem/pc-dimm.c index 50ef83215c..192fc7922c 
100644
--- a/hw/mem/pc-dimm.c
+++ b/hw/mem/pc-dimm.c
@@ -81,6 +81,7 @@ void pc_dimm_plug(PCDIMMDevice *dimm, MachineState *machine)
 
     memory_device_plug(MEMORY_DEVICE(dimm), machine);
     vmstate_register_ram(vmstate_mr, DEVICE(dimm));
+    machine->device_memory->dimm_size += vmstate_mr->size;
 }
 
 void pc_dimm_unplug(PCDIMMDevice *dimm, MachineState *machine) @@ -90,6 +91,7 
@@ void pc_dimm_unplug(PCDIMMDevice *dimm, MachineState *machine)
 
     memory_device_unplug(MEMORY_DEVICE(dimm), machine);
     vmstate_unregister_ram(vmstate_mr, DEVICE(dimm));
+    machine->device_memory->dimm_size -= vmstate_mr->size;
 }
 
 static int pc_dimm_slot2bitmap(Object *obj, void *opaque) diff --git 
a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c index 
746f07c4d2..40fa40109d 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 != NULL) {
+        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) @@ -776,7 +753,11 
@@ static void virtio_balloon_set_config(VirtIODevice *vdev,
     VirtIOBalloon *dev = VIRTIO_BALLOON(vdev);
     struct virtio_balloon_config config;
     uint32_t oldactual = dev->actual;
-    ram_addr_t vm_ram_size = get_current_ram_size();
+    ram_addr_t vm_ram_size;
+    ram_addr_t vm_ram_size_new;
+
+retry:
+    vm_ram_size = get_current_ram_size();
 
     memcpy(&config, config_data, virtio_balloon_config_size(dev));
     dev->actual = le32_to_cpu(config.actual); @@ -784,6 +765,11 @@ static void 
virtio_balloon_set_config(VirtIODevice *vdev,
         qapi_event_send_balloon_change(vm_ram_size -
                         ((ram_addr_t) dev->actual << 
VIRTIO_BALLOON_PFN_SHIFT));
     }
+    vm_ram_size_new = get_current_ram_size();
+    if (vm_ram_size_new != vm_ram_size) {
+        goto retry;
+    }
+
     dev->poison_val = 0;
     if (virtio_balloon_page_poison_support(dev)) {
         dev->poison_val = le32_to_cpu(config.poison_val); diff --git 
a/include/hw/boards.h b/include/hw/boards.h index 6fbbfd56c8..551b4b419e 100644
--- a/include/hw/boards.h
+++ b/include/hw/boards.h
@@ -296,6 +296,7 @@ struct MachineClass {  typedef struct DeviceMemoryState {
     hwaddr base;
     MemoryRegion mr;
+    ram_addr_t dimm_size;
 } DeviceMemoryState;
 
 /**
--
2.33.0