So my hope, eventually, is to have my own purpose-built computer which is an expandable skeleton and will more-or-less never need to be entirely tossed out, only supplanted/upgraded Ship of Theseus style.
However, Microsoft is getting a bit too uppity for my tastes, and I hope to mainly run Linux on that eventual computer.
However, I'm also a gaming man, and I recognize that, in many cases, Linux kinda sucks for games, or, at least, that's what I've heard. Emulation is also a pain I'd rather not deal with (both of Windows and of games themselves), and so, for games that don't support Linux, I'd like to have the option of having Windows on the same machine, so that I can run Linux most of the time, but switch to Windows whenever I wanna play games.
My question is how realistic is that? I know that machines with multiple OS's exist, and you can choose which one you want at boot, but I'm hoping for this to be an extremely fancy computer, connected to a lot of extremely fancy computer peripherals. Would switching OS's without power cycling the machine screw with the other hardware? Is it even possible, or would you need to power cycle it in any case? Is there any way to build this hypothetical computer, or am I asking too much/investing too much effort? Would it be easier/better to just build a really good Windows machine and a really good Linux machine?
So the use case you're talking about is pretty popular among a certain kinds of Tech Nerd, and most of them solve it with iommu GPU Passthrough and a windows VM on Linux. I knew a few people doing this back in like 2018 and while it's a little fidgety it's fairly reliable.
You can't share GPU's the way you can share CPU and Memory. Not on consumer hardware, anyway. So if you want to run a VM with windows with a gaming GPU, it needs its own entire GPU just for that.
The basic layout is this: Build a normal high end system with a lot of extra resources, say, 32+GB of RAM, 10+ CPU cores, a couple terabytes of storage, and two separate GPU's. Run Linux on the system, as your host, and only use one of the GPU's. Create a VM on the host under qemu and hand it 16GB of RAM, 6 cores, a terabyte or two of storage, and use iommu to pass it the other GPU. Now use software like LookingGlass to capture the framebuffer directly off the Windows GPU and forward it to your Linux GPU, so that you can display your windows system inside Linux seamlessly.
Now, you do need two GPU's, so it can get expensive. A lot of people choose to run one higher end GPU for windows and a basic GPU for Linux, but that's up to your use case. You can run two identical GPU's if you wish.
The main place this kind of thing is being tinkered with is the Level1Techs forum, Wendell is a big advocate of GPU virtualization and so has aggregated a lot of information and people with relevance here. He also makes a lot of video stuff on IOMMU.
So I have to have two whole GPU's?
Kind of. There ARE ways to live-reset a running GPU which allows you to do tricks where you can swap a single GPU between the host and the VM without rebooting, but it's extremely dubious and flaky. Virtualized GPU partitioning exists but only on extremely expensive server GPU's aimed at virtualization servers for enterprise so it's well outside of our price range.
If you're interested in single-GPU, there is ongoing work getting it to run on consumer hardware on the Level1Techs forum and he's even running some kind of Hackathon on it, but even the people having success with this have pretty unreliable systems.
https://forum.level1techs.com/t/vfio-passthrough-in-2023-call-to-arms/199671
This setup works fine maybe 25% of the time. I can always start the VM just fine, my linux desktop stays active and any software launched after the VM gets the GPU will render on the iGPU without issues. However I suffer from the reset bug, and 75% of the time shutting down the VM won’t return the GPU to Linux and I have to reboot to fix that.
I'm quite satisfied with this setup.
Is this a good idea
It depends on what you need and how willing you are to switch between the host and VM. A LOT more things run smoothly on Linux these days. Wendell started tinkering with IOMMU back in like 2015, and I started gaming on Linux back in 2016. If you had native software, great! Without that, well, good luck with anything less than five years old.
I played Burnout Paradise and even Subnautica on my 750Ti laptop on plain old Wine, and then DXVK came out in 2018 and the world got flipped turned upside down and I have video of me running Warframe on Linux with that same mediocre system a few weeks before Proton hit the scene and we got flipped turned... right way up? Now with Proton I would say most things run pretty well under a mixture of automatic steam stuff and scripts off lutris and homemade WINEPREFIXes.
That said, if you want everything to Just Work, it's hard to beat a VM. I'm not sure how competitive games run, but for everything else a VM is going to be more reliable than WINE.
