Microsoft is to overhaul Windows’ graphic driver model after realising that the Windows Display Driver Model (WDDM) 1.0 AÂ¢aâÂ¬” which will ship with Vista AÂ¢aâÂ¬” needs improvement in the way it shares GPU resources between programs and Windows itself.
Steve Pronovost of Microsoft’s DirectX team disclosed at WinHEC in Seattle last week that although the WDDM 1.0 introduces some rudimentary task scheduling for GPUs a new generation of GPU hardware and a major architectural change to the way Windows deals with video cards will be required.
He said that the trouble with WDDM 1.0 is that once one program is using the GPU other programs are shut out until the process completes. In Vista that can cause less fluid rendering of on-screen graphics if multiple programs are trying to use GPU resources at once.
Until now the inability to share GPU resources hasn’t been an obvious problem under Windows XP because XP uses GDI AÂ¢aâÂ¬” a 2D graphics system AÂ¢aâÂ¬” to draw windows and operating system interface elements. In general only 3D games and other major grahics apps use GPU resources and users only run one such app at a time he said.
However inadequate GPU sharing is a problem for Windows Vista because it uses the GPU to draw all elements of Vista’s new Aero interface and more generally there is a trend towards using the massive computing power in GPUs to process an array of non-graphics tasks as well.
The gotcha is that improving GPU task scheduling will require new hardware he said. The overhauled device driver model WDDM 2.0 will only run on a new yet-to-be-released generation of GPUs. NVIDIA and ATI are already aware of Microsoft’s plans and are working on new hardware.
However it means that what is a Windows Vista logo-compliant machine today may not be able to optimally run future iterations of Windows incorporating WDDM 2.0.
Microsoft is also looking at a further revision of the standard WDDM 2.1 which will run on the same hardware as 2.0 but offer even finer-grained multitasking on the GPU.
Henry Moreton of NVIDIA said the power of GPUs was finally being tapped by application developers. For example he said a Windows Vista desktop PC user could easily be running the Windows Vista Desktop Manager (WDM) GPU-aware photo editing software video feed viewers and TV PVR applications simultaneously.
“Some GPU operations are so massive they take a non-trivial amount of time to complete” he said “while Other GPU operations are time sensitive.”
Pronovost did not say when Microsoft expected WDDM 2.0 and 2.1 to be introduced into Windows and Microsoft said it “did not have any information to share” in response to an APC enquiry.
Microsoft also talked at WinHEC about how it was introducing I/O scheduling for Vista so disk-intensive tasks such as virus scanning or large file copy operations couldn’t cause a system to become unresponsive.
Dan Warne travelled to Windows Hardware Engineering Conference 2006 in Seattle as a guest of Microsoft.