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  Új Válasz 2023-03-31 20:08:48 #60752

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  D3D12 GPU Upload Heaps
  https://github.com/microsoft/DirectX-Specs/commit/808d66358976f2c88f59d8bdf46504cc4b4b0514
  ( committed yesterday )

  "It used to be typical for a discrete GPU to have only a small portion of its frame buffer exposed over the PCI bus. D3D chose not to expose this because the I/O region for a frame buffer is usually only 256MB, which is not that useful. A bigger problem was that it's not a properly virtualizable resource. If app A comes in and allocates all 256MB, then app B wouldn't be able to allocate any. So we can't provide any guarantees around it, at which point it seemed like a bad idea to expose to apps.

  However, now there are a lot of GPUs that support a resizable base address register(also known as Resizable BAR). With a resizable bar, Windows will renegotiate the size of a GPU's BAR in WDDM Version 2.0 and later. Another good reason for D3D12 to expose Resizable BAR is that some performance testing on some platforms has shown that games perform better with resizeable BAR enabled.

  D3D now decides to support the use of CPU visible VRAM via D3D GPU upload heaps on both discrete and integrated GPUs.

  One reason to use GPU upload heaps on integrated GPUs is that you can use GPU upload heaps instead of using upload + default heaps for resources, so there's no need to do a lot of copy operations just to put the resource in a different state. Alternatively this optimization can be done via UMA Optimizations: CPU Accessible Textures and Standard Swizzle."
  
  +
  https://devblogs.microsoft.com/directx/preview-agility-sdk-1-710-0/
  "
  Historically a GPU’s VRAM was inaccessible to the CPU, forcing programs to have to copy large amounts of data to the GPU via the PCI bus. Most modern GPUs have introduced VRAM resizable base address register (BAR) enabling Windows to manage the GPU VRAM in WDDM 2.0 or later.
  With the VRAM being managed by Windows, D3D now exposes the heap memory access directly to the CPU! This allows both the CPU and GPU to directly access the memory simultaneously, removing the need to copy data from the CPU to the GPU increasing performance in certain scenarios. "

  [ Szerkesztve ]

  Mottó: "A verseny jó!"

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