They are submitted along a command buffer and are used to patch command buffers to actual physical addresses before submission to an engine. In the physical mode the user-mode driver continues to generate the allocation and patch location lists.

In the physical mode, the scheduling model remains the same as it is with WDDM v1.x. Individual engines of a GPU can operate in either physical or virtual mode: This allows the user-mode driver to reference allocations through their GPU virtual address without having to worry about the underlying physical memory changing through its lifetime. An allocation, created or opened by a process, gets assigned a unique GPU virtual address within that process GPU virtual address space that remains constant and unique for the lifetime of the allocation.

In this model, each process gets assigned a unique GPU virtual address space in which every GPU context to execute in. To achieve this, WDDM v2 supports GPU virtual addressing. This tracking and patching was expensive and essentially imposed a scheduling model where the video memory manager (VidMm) had to inspect every packet before it could be submitted to an engine.Īs more hardware vendors moved toward a hardware-based scheduling model, where work is submitted to the GPU directly from user mode and where the GPU manages the various queue of work itself, it became necessary to eliminate the need for VidMm to inspect and patch every command buffer before submission to a GPU engine. This led to the need to track memory references inside command buffers through allocation and patch location lists, and to patch those buffers with the correct physical memory reference before submission to a GPU engine. As segments were shared across applications and over-committed, resources got relocated through their lifetime and their assigned physical addresses change. Under Windows Display Driver Model (WDDM) v1.x, the device driver interface (DDI) was built such that graphics processing unit (GPU) engines were expected to reference memory through segment physical addresses. This functionality is available starting with Windows 10. This section provides details about GPU virtual memory, including why the changes were made and how drivers use it.

Directx 12 wddm 2.0