On Wed, 20 May 2020 at 02:33, Sasha Levin <sashal@xxxxxxxxxx> wrote: > > There is a blog post that goes into more detail about the bigger > picture, and walks through all the required pieces to make this work. It > is available here: > https://devblogs.microsoft.com/directx/directx-heart-linux . The rest of > this cover letter will focus on the Linux Kernel bits. > > Overview > ======== > > This is the first draft of the Microsoft Virtual GPU (vGPU) driver. The > driver exposes a paravirtualized GPU to user mode applications running > in a virtual machine on a Windows host. This enables hardware > acceleration in environment such as WSL (Windows Subsystem for Linux) > where the Linux virtual machine is able to share the GPU with the > Windows host. > > The projection is accomplished by exposing the WDDM (Windows Display > Driver Model) interface as a set of IOCTL. This allows APIs and user > mode driver written against the WDDM GPU abstraction on Windows to be > ported to run within a Linux environment. This enables the port of the > D3D12 and DirectML APIs as well as their associated user mode driver to > Linux. This also enables third party APIs, such as the popular NVIDIA > Cuda compute API, to be hardware accelerated within a WSL environment. > > Only the rendering/compute aspect of the GPU are projected to the > virtual machine, no display functionality is exposed. Further, at this > time there are no presentation integration. So although the D3D12 API > can be use to render graphics offscreen, there is no path (yet) for > pixel to flow from the Linux environment back onto the Windows host > desktop. This GPU stack is effectively side-by-side with the native > Linux graphics stack. Okay I've had some caffiene and absorbed some more of this. This is a driver that connects a binary blob interface in the Windows kernel drivers to a binary blob that you run inside a Linux guest. It's a binary transport between two binary pieces. Personally this holds little of interest to me, I can see why it might be nice to have this upstream, but I don't forsee any other Linux distributor ever enabling it or having to ship it, it's purely a WSL2 pipe. I'm not saying I'd be happy to see this in the tree, since I don't see the value of maintaining it upstream, but it probably should just exists in a drivers/hyperv type area. Having said that, I hit one stumbling block: "Further, at this time there are no presentation integration. " If we upstream this driver as-is into some hyperv specific place, and you decide to add presentation integration this is more than likely going to mean you will want to interact with dma-bufs and dma-fences. If the driver is hidden away in a hyperv place it's likely we won't even notice that feature landing until it's too late. I would like to see a coherent plan for presentation support (not code, just an architectural diagram), because I think when you contemplate how that works it will change the picture of how this driver looks and intergrates into the rest of the Linux graphics ecosystem. As-is I'd rather this didn't land under my purview, since I don't see the value this adds to the Linux ecosystem at all, and I think it's important when putting a burden on upstream that you provide some value. Dave.
