IDirect3DDevice9Ex::SetGPUThreadPriority method (d3d9.h)
Set the priority on the GPU thread.
HRESULT SetGPUThreadPriority( [in] INT Priority );
The thread priority, ranging from -7 to 7.
Possible return values include: D3D_OK, D3DERR_INVALIDCALL, or D3DERR_DEVICEREMOVED (see D3DERR).
GPU thread priority is not reset when a device is lost. The effects of calls to this method are not recorded in state blocks.