WPF Primitive Element could still uses Sofware Rendering

The following simple Animation strangely still uses swIRT shown in Perforator.

It turns out that WPF Rendering pipe need to rasterize DrawingBrush in software and hand over to GPU. And the only solution is to use RenderingOption,CachingHint on DrawingBrush

<Window x:Class="WpfApplication5.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">

    <Window.Resources>
        <DrawingBrush x:Key="MyBlueGridBrushResource" Viewport="0,0,10,10" ViewportUnits="Absolute" TileMode="Tile"
                      RenderOptions.CachingHint="Cache"
                      RenderOptions.CacheInvalidationThresholdMaximum="1000" RenderOptions.CacheInvalidationThresholdMinimum="0.5">
            <DrawingBrush.Drawing>
                <DrawingGroup>
                    <DrawingGroup.Children>
                        <GeometryDrawing Brush="White">
                            <GeometryDrawing.Geometry>
                                <RectangleGeometry Rect="0,0,1,1" />
                            </GeometryDrawing.Geometry>
                        </GeometryDrawing>
                      
                    </DrawingGroup.Children>
                </DrawingGroup>
            </DrawingBrush.Drawing>
        </DrawingBrush>
    </Window.Resources>

    <DockPanel Margin="10">
        <Canvas Width="250" Height="250"  Background="{StaticResource MyBlueGridBrushResource}">
            <Rectangle
            Height="50" Width="50" Fill="#CCCCCCFF" Stroke="Blue" StrokeThickness="2"
            Canvas.Left="100" Canvas.Top="100">
                <Rectangle.RenderTransform>
                    <ScaleTransform x:Name="MyAnimatedScaleTransform" CenterX="25" CenterY="25" ScaleX="1" ScaleY="1" />
                </Rectangle.RenderTransform>
            </Rectangle>
            <Rectangle Height="50" Width="50" Stroke="#99000000"
            StrokeDashArray="4,1" StrokeThickness="2"
            Canvas.Left="100" Canvas.Top="100" />
        </Canvas>
        <DockPanel  HorizontalAlignment="Center" VerticalAlignment="Bottom"
        Margin="10">
            <Button Name="startButton" Margin="0,0,2,0">Start</Button>
            <DockPanel.Triggers>
                <EventTrigger SourceName="startButton" RoutedEvent="Button.Click">
                    <BeginStoryboard Name="myBeginStoryboard">
                        <Storyboard>
                            <DoubleAnimation 
                  Storyboard.TargetName="MyAnimatedScaleTransform" 
                  Storyboard.TargetProperty="ScaleX" 
                  From="0" To="5" Duration="0:0:2" />
                            <DoubleAnimation 
                  Storyboard.TargetName="MyAnimatedScaleTransform" 
                  Storyboard.TargetProperty="ScaleY" 
                  From="0" To="5" Duration="0:0:2" />
                        </Storyboard>
                    </BeginStoryboard>
                </EventTrigger>
            </DockPanel.Triggers>
        </DockPanel>
    </DockPanel>
</Window>