Radeon 1600, DirectX 9, resolving MSAA z-buffer with StretchRect() works very slow

Discussion created by hax666 on Feb 23, 2008
Latest reply on Mar 16, 2008 by avk
DirectX 9, we are resolving MSAA z-buffer to non-MSAA zbuffer, and then using it for rendering with RenderTarget texture. This helps us to lower fillrate during postprocessing (some of our postprocessing effects require z-compare). All surfaces have same width/height, zbuffer is not discardable, StretchRect() is called between EndScene()/BeginScene().
FPS is 3-4. Works fine on nVidia cards.
Is this driver issue, or hardware just can't handle this efficiently?