Multi-Adapter Support in DirectX* 12

Download Code Sample   Download PDF


This sample shows how to implement an explicit multi-adapter application using DirectX 12. Intel’s integrated GPU (iGPU) and a discrete NVIDIA GPU (dGPU) are used to share the workload of ray-tracing a scene. The parallel use of both GPUs allows for an increase in performance and for more complex workloads.

This sample uses multiple adapters to render a simple ray-traced scene using a pixel shader. Both adapters render a portion of the scene in parallel.

Explicit Multi-Adapter Overview

Support for explicit multi-adapter is a new feature in DirectX 12. This feature allows for the parallel use of multiple GPUs regardless of manufacturer and type (for example, integrated or discrete). The ability to separate work across multiple GPUs is provided by the presence of independent resource management and parallel queues for each GPU at the API level.

DirectX 12 introduces two main API features that help enable multi-adapter applications:

  • Cross-adapter memory that is visible to both adapters.

    DirectX 12 introduces cross-adapter-specific resource and heap flags:
    The cross-adapter resources exist in memory on the primary adapter and can be referenced from another adapter with minimal cost.

  • Parallel queues and cross-adapter synchronization that allows for parallel execution of commands. A special flag is used when creating a synchronization fence: D3D12_FENCE_FLAG_SHARED_CROSS_ADAPTER.

    A cross-adapter fence allows a queue on one adapter to be signaled by a queue on the other.

    The above diagram shows the use of three queues to facilitate copying into cross-adapter resources. This is the technique used in this sample and showcases the following steps:
    1. Queue 1 on GPU A and Queue 1 on GPU B render portions of a 3D scene in parallel.
    2. When rendering is complete, Queue 1 signals, allowing Queue 2 to begin copying.
    3. Queue 2 copies the rendered scene into a cross-adapter resource and signals.
    4. Queue 1 on GPU B waits for Queue 2 on GPU A to signal and combines both rendered scenes into the final output.

Cross-Adapter Implementation Steps

Incorporating a secondary adapter into a DirectX 12 application involves the following steps:

  1. Create cross-adapter resources on the primary GPU as well as a handle to these resources on the secondary GPU.
    // Describe cross-adapter shared resources on primaryDevice adapter
    D3D12_RESOURCE_DESC crossAdapterDesc = mRenderTargets[0]->GetDesc();
    crossAdapterDesc.Flags = D3D12_RESOURCE_FLAG_ALLOW_CROSS_ADAPTER;
    crossAdapterDesc.Layout = D3D12_TEXTURE_LAYOUT_ROW_MAJOR;
    // Create a shader resource and shared handle
    for (int i = 0; i < NumRenderTargets; i++)
        HANDLE heapHandle = nullptr;
        // Open shared handle on secondaryDevice device
        mSecondaryDevice->OpenSharedHandle(heapHandle, IID_PPV_ARGS(&shaderResourceViews[i]));
    // Create a shader resource view (SRV) for each of the cross adapter resources
    CD3DX12_CPU_DESCRIPTOR_HANDLE secondarySRVHandle(mSecondaryCbvSrvUavHeap->GetCPUDescriptorHandleForHeapStart());
    for (int i = 0; i < NumRenderTargets; i++)
        mSecondaryDevice->CreateShaderResourceView(shaderResourceViews[i].Get(), nullptr, secondarySRVHandle);
  2. Create synchronization fences for the resources that are shared between both adapters.
    // Create fence for cross adapter resources
    // Create a shared handle to the cross adapter fence
    HANDLE fenceHandle = nullptr;
    // Open shared handle to fence on secondaryDevice GPU
    mSecondaryDevice->OpenSharedHandle(fenceHandle, IID_PPV_ARGS(&secondaryFence));
  3. Render on primary GPU into an offscreen render target, and signal queue on completion.
    // Render scene on primary device
    mPrimaryCommandQueue->ExecuteCommandLists(1, primaryCommandList);;
    // Signal primary device command queue to indicate render is complete
    mPrimaryCommandQueue->Signal(mPrimaryFence.Get(), currentFenceValue));
    fenceValues[currentFrameIndex] = currentFenceValue;
  4. Copy resources from offscreen render target into cross-adapter resources, and signal queue on completion.
    // Wait for primary device to finish rendering the frame
    mCopyCommandQueue->Wait(mPrimaryFence.Get(), fenceValues[currentFrameIndex]);
    // Copy from off-screen render target to cross-adapter resource
    mCopyCommandQueue->ExecuteCommandLists(1, crossAdapterResources->mCopyCommandLists.Get());
    // Signal secondary device to indicate copy is complete
    mCopyCommandQueue->Signal(mPrimaryCrossAdapterFence.Get(), mCurrentCrossAdapterFenceValue));
    mCrossAdapterFenceValues[mCurrentFrameIndex] = mCurrentCrossAdapterFenceValue;
  5. Render on secondary GPU, using handle to cross-adapter resource to access resources as a texture.
    // Wait for primary device to finish copying
    mSecondaryCommandQueue->Wait(mSecondaryCrossAdapterFence.Get(), mCrossAdapterFenceValues[mCurrentFrameIndex]));
    // Render cross adapter resources and segmented texture overlay on secondary device
    mSecondaryCommandQueue->ExecuteCommandLists(1, secondaryCommandList);
  6. Secondary GPU displays frame to screen.
    mSwapChain->Present(0, 0);

Note that the code provided above has been modified for simplification with all error checking removed. It is not expected to compile.

Performance and Results

Using multiple adapters to render a scene in parallel yields a significant increase in performance compared to relying on a single adapter to perform the entire rendering workload.

Figure 1. Frame time of 100 frames in milliseconds versus work split between integrated and discrete cards.

In the sample ray-traced scene, a decrease of approximately 26 milliseconds was observed when both an NVIDIA GeForce* 840M and Intel® HD Graphics 5500 were used to share the rendering load.

By parallelizing the workload, it is possible to reduce the frame time required by nearly 50 percent compared to using a single adapter.

Note that the workload shown in this sample is easily parallelizable and may not immediately translate to real-world gaming applications.

Appendix: Sample Architecture Overview

This sample can be downloaded from  Github. It is architected as follows:

  • WinMain.cpp
    • Entry point to the application
    • Creates objects and instantiates renderer
  • DXDevice.cpp
    • Encapsulates ID3D12Device object alongside related objects
    • Contains command queue, allocator, render targets, fences, and descriptor heaps
  • DXRenderer.cpp
    • Base renderer class
    • Implements shared functionality (for example, creating vertex buffer or updating texture)
  • DXMultiAdapterRenderer.cpp
    • Perform all core, implementation-specific rendering functionality (that is, set up pipeline, load assets, and populate command lists)
  • DXCrossAdapterResources.cpp
    • Abstracts creation and updating of multi-adapter resources
    • Handles copying of resources and fencing between both GPUs

DXMultiAdapterRenderer.cpp consists of the following functions:

    DXMultiAdapterRenderer(std::vector<DXDevice*> devices, MS::ComPtr<IDXGIFactory4> dxgiFactory, UINT width, UINT height, HWND hwnd);
    virtual void OnUpdate() override;
    float GetSharePercentage();
    void IncrementSharePercentage();
    void DecrementSharePercentage();
    virtual void CreateRootSignatures() override;
    virtual void LoadPipeline() override;
    virtual void LoadAssets() override;
    virtual void CreateCommandLists() override;
    virtual void PopulateCommandLists() override;
    virtual void ExecuteCommandLists() override;
    virtual void MoveToNextFrame() override;

This class implements all the core rendering functionality. The LoadPipeline() and LoadAssets() functions are responsible for creating all necessary root signatures, compiling shaders, and creating pipeline state objects as well as specifying and creating all textures, constant buffers, and vertex buffers and their associated views. All necessary command lists are created at this time as well.

For each frame, PopulateCommandLists() and ExecuteCommandLists() are called.

In order to separate the traditional DirectX 12 rendering functionality from that which is necessary for using multiple-adapters, all of the necessary cross-adapter functionality is encapsulated in the DXCrossAdapterResources class, which contains the following functions:

    DXCrossAdapterResources(DXDevice* primaryDevice, DXDevice* secondaryDevice);
    void CreateResources();
    void CreateCommandList();
    void PopulateCommandList(int currentFrameIndex);
    void SetupFences();

The CreateResources(), CreateCommandList(), and SetupFences() functions are all called upon initialization to create the cross-adapter resources and initialize the synchronization objects.

Every frame, the PopulateCommandList() function is called to populate the copy command list.

The DXCrossAdapterResources class contains a separate command allocator, command queue, and command list that are used for copying resources from a render target on the primary adapter into the cross-adapter resources.

About the Author

The author of this article is Nicolas Langley, who is an intern working with Intel's Visual Computing Software Division on Multi-Adapter Support in DirectX* 12 project.


Intel technologies may require enabled hardware, specific software, or services activation. Performance varies depending on system configuration. Check with your system manufacturer or retailer.

Software and workloads used in performance tests may have been optimized for performance only on Intel microprocessors. Performance tests, such as SYSmark* and MobileMark*, are measured using specific computer systems, components, software, operations and functions. Any change to any of those factors may cause the results to vary. You should consult other information and performance tests to assist you in fully evaluating your contemplated purchases, including the performance of that product when combined with other products.

No license (express or implied, by estoppel or otherwise) to any intellectual property rights is granted by this document.

Intel disclaims all express and implied warranties, including without limitation, the implied warranties of merchantability, fitness for a particular purpose, and non-infringement, as well as any warranty arising from course of performance, course of dealing, or usage in trade.

This document contains information on products, services and/or processes in development. All information provided here is subject to change without notice. Contact your Intel representative to obtain the latest forecast, schedule, specifications and roadmaps.

The products and services described may contain defects or errors known as errata which may cause deviations from published specifications. Current characterized errata are available on request.

Copies of documents which have an order number and are referenced in this document may be obtained by calling 1-800-548-4725 or by visiting

Intel and the Intel logo are trademarks of Intel Corporation in the U.S. and/or other countries.

*Other names and brands may be claimed as the property of others

© 2015 Intel Corporation.

For more complete information about compiler optimizations, see our Optimization Notice.