Isn't WSL2 just a VM?

by sedatk • 8 months ago

175 112 8 months ago

mindcrash• 8 months ago

WSL 2 runs on a subset of Hyper-V, and on a hypervisor, so basically yes.

However, there's some interesting things going on in WSL 2 versus a "normal" Hyper-V virtual machine. For example, a Linux distro running on WSL can (and will) use GPU partitioning (aka PCI/GPU passthrough) and a special implementation of DirectX enabling the installed video card to accelerate graphics within X and/or Wayland.

Although this feature can be enabled with a lot of hacking in both the Linux guest and vanilla Hyper-V on the host (the latter through Powershell) it is officially unsupported on Windows 10 and Windows 11, and is only supported on Windows Server.

sedatk3• 8 months ago

Oh, I thought GPU passthrough was enabled on vanilla Windows 11, but I didn't delve into that feature enough. It's still extremely impressive of course. Perhaps I should write another article about graphical features.

DiabloD3• 8 months ago

No, PCI-E passthrough is not enabled on non-Server, and you arguably wouldn't do this on a Windows hypervisor. anyways, you'd do it with a Linux+KVM hypervisor for either Linux or Windows guests.

Using GPU passthrough, however, is allowed. WSL2 does this by using the existing Mesa/DRI/DRM open source stack, but instead of a GPU-specific DRM driver, it is one that speaks WDDM (the DRM equivalent in the Windows driver stack), and only requires a GPU-specific ennoblement package (provided by the vendor, and matches the Windows driver it is talking to; AMD, Nvidia, and Intel all ship one inside of WSL2).

my123• 8 months ago

Regular Hyper-V VMs can use it too but it's not well documented.

The keyword to search for: "GPU-P"

https://learn.microsoft.com/en-us/windows-server/virtualizat...

evanjrowley• 8 months ago

https://learn.microsoft.com/en-us/windows-server/virtualizat...

It relies upon SR-IOV and only several server-specific Nvidia GPUs are listed as supported.

Intel's Flex dGPUs and Arc iGPUs have supported SR-IOV for years now, but they aren't listed there. It would be super awesome if Microsoft could add it for Intel Arc iGPUs, desktop versions of Windows, and WSL2! Intel's GPU SR-IOV already works with KVM on Linux!

rusk• 8 months ago

Thus far I have found the native WSL2 graphics integration to be pretty disappointing in comparison to what I used to get with X-server setup. Unfortunately the legacy X implementation doesn’t have the modern API and application developers are tapering their interest in it. Hopefully the groundswell of WSL2 support will improve this in time …

danjl• 8 months ago

Agreed. No way to really test WebGPU, for instance. You can't really test GPU drivers under Linux or using the native Windows browsers. Lots of incomplete attempts to make this work, none of which are reliable or easy to use.

user34283• 8 months ago

Same here, but maybe for different reasons.

As an end user, the out of the box experience of getting a blurry window with the wrong content size isn't very useful. And I've never tried to actually configure it properly.

I wonder if it's a decent experience even when configured properly. In that case, why do all the IDEs come with remote development / WSL integrations that involve running the client on the Windows side?

nine_k• 8 months ago

Don't WSL2 and the WinNT kernel both run on top of Hyper-V, on (very approximately) equal footing? The NT kernel, of course, has all the hardware access, not necessarily granted to other VMs, such as WSL2.

p_ing2• 8 months ago

See https://learn.microsoft.com/en-us/windows-server/virtualizat....

bogwog• 8 months ago

and is only supported on Windows Server.

Imagine licensing and installing Windows Server to run Linux software through WSL

someguy101010• 8 months ago

clearly you have never worked in enterprise

lukeschlather• 8 months ago

There are a variety of applications that it's not really possible to run natively on Linux, for example Widevine L1. I don't think there are any applications that can't run through WSL.

pjmlp7• 8 months ago

It is actually a product people pay for,

https://learn.microsoft.com/en-us/azure/iot-edge/tutorial-de...

CoolCold• 8 months ago

I'm 99% sure ive seen such questions/requests on Reddit for Windows server.

arghwhat2• 8 months ago

For example, a Linux distro running on WSL can (and will) use GPU partitioning (aka PCI/GPU passthrough) and a special implementation of DirectX

That is still just a normal VM, but it's nice that it's automated.

enabling the installed video card to accelerate graphics within X and/or Wayland.

nit: X and/or Wayland is not involved in application rendering at all - its applications themselves that use the GPU and its acceleration directly.

Wayland and/or X is only involved when the apps are all done rendering[0], and the display servers own rendering is the comparatively simple task of stitching windows together[1], and sometimes not even that.

0: You can send buffers early over Wayland if you also send a sync fence, but this is just forwarded as a render dependency that the GPU scheduler will patiently wait for.

1: well also dealing with stuff like color transforms which can be complex to understand, but are computationally cheap and for fullscreen content possibly entirely free.

kiddico• 8 months ago

How did you learn about the things in [0]? Idk where to even start.

andix11• 8 months ago

Yes, it's "just" a VM.

WSL2 is a bit like Firecracker for Linux. It's a lightweight VM, with a lot of optimizations here and there. For faster startup, lower memory footprint and so on.

PS: which means you need a lot of memory, if you use WSL2 extensively (multiple Docker containers for example). 8-16 GB on top of your usual workloads is a good starting point. Docker on WSL2 is not a lot of fun with less than 20 GB system memory.

nu11ptr• 8 months ago

For faster startup, lower memory footprint and so on

Any idea how they do this? My WSL2 starts insanely fast, like about 1-2 seconds. I've never seen a linux distro natively boot that fast. Assuming they suppress any sort of BIOS startup screen for starters, but what else?

andix11• 8 months ago

Actually I don't know it either. But WSL2 doesn't really start a lot of processes, like a desktop/server Linux distribution. It starts up only a minimal set of processes, and a shell.

dmesg looks like the kernel is booting up normally, so I guess they don't use some memory snapshots magic.

I guess they just tweaked the kernel and the hypervisor to start up fast. There is also no BIOS/UEFI delay.

sedatk3• 8 months ago

It’s a very trimmed down kernel with minimal set of drivers and modules. It doesn’t even support SD cards out of the box. That’s probably the main reason as no hardware probing/initialization delays are incurred.

em500• 8 months ago

At high level, WSL2 provides a single optimized VM and Microsoft-compiled Linux kernel. Optimized here means that the VM only provides a small set of devices to the Linux kernel, and the kernel operates with exact known hardware, which is much smaller and simpler compared to a full blown kernel (which detects a large variety of hardware) and fuller featured VMs (c.f. qemu emulated devices: https://kashyapc.fedorapeople.org/virt/qemu/qemu-list-of-emu...).

And when you run multiple "distributions" or instances, they all share the same running VM and kernel. So after a one-time startup of the VM+kernel, opening more distributions/instances is like starting new system containers (similar to lxc/lxd or systemd-nspawn, which are also very quick to spawn on Linux) rather than new VMs. The architecture is quite similar to Linux-on-ChromeOS (Crostini).

pjmlp7• 8 months ago

Thankfully getting laptops with 32 GB on PC land isn't the same as paying Apple premium.

andix11• 8 months ago

I guess you didn't check the latest memory prices. 64 GB used to be dirt cheap, but not anymore.

antonkochubey• 8 months ago

if you're buying 'gaming' laptops - sure, but in business laptop world, Lenovo/Dell/HP premiums on RAM and SSD can be much higher than Apple's.

pak9rabid• 8 months ago

Yes, a VM with extremely tight integration with the Windows environment to make things that would otherwise require lots of time to setup a breeze. I use it as my daily driver for dev work (at work, since we're required to use Windows :( ) and to be honest it's quite pleasant most of the time.

scuff3d• 8 months ago

I usually work in a VM hosted by my company. But the performance is really starting to irritate me. Been considering switching to WSL2, but last time I checked all they supported was Debian based distros, and we do all our work on RHEL8. I don't think it would matter much but it's still annoying working on an entirely different setup from the rest of the team.

How is the graphical app support these days?

spockz• 8 months ago

You can create your own images: https://learn.microsoft.com/en-us/windows/wsl/build-custom-d...

Or more step by step: https://gist.github.com/artman41/858450e2c29b239d8692213b684...

pod_krad• 8 months ago

They support Oracle Linux. It is almost the same as RHEL.

stackedinserter• 8 months ago

How is it "tight" when even `ps` or `top` show VM processes instead of OS ones? Could you give an example of functionality that can't be done with `docker run -it ubuntu`?

I used it for a little bit (got Windows laptop, thought maybe I'll switch but no), and just hated that split brain workspace.

baq• 8 months ago

you can access the internal VM disk via

    \\wsl$

UNC and you should be able to easily subst a drive letter for the dumb software from eons ago that doesn't support UNC paths.

Thaxll• 8 months ago

I always found wsl to be a hack and not a true Linux distro, fake pid 1 not really starting or shutting down ect... Even the docker integration is really odd. I know it was fixed with wsl2 but wsl1 had terrible i/o performance.

bangaladore• 8 months ago

Imo, WSL2 is almost indistinguishable from a true Ubuntu VM. If you haven't tried it since WSL1, I'd give it a shot.

Of course this comes down to whether you care or not about the integrations with Windows.

firesteelrain• 8 months ago

We use it work to do things on WSL2 in Azure Desktop that don’t require a Linux VM and using Windows versions of tools that feel clunky like helm, kubectl, etc. We can easily interface with ACR and AKS this way.

creata• 8 months ago

Linux and Win32 filesystem APIs were too different, and translating them made some apps and some workflows seriously suffer.

Is the reverse also true? Does Wine face any similar performance problems?

andix11• 8 months ago

I guess the main issue is, that Windows filesystem APIs are slow. Windows does a lot of things when opening/closing file handles (acls, virus scanning, and many more). Unix style applications with a lot of small files just perform really poorly. That's also why npm install takes ages on Windows.

They made it much better with Dev Drives, that use ReFS instead of NTFS and disables most of the filters in the filesystem stack.

Gabrys1• 8 months ago

The file operations on macOS are rather slow too. I needed to invest in some rsync-based syncing for an in-docker application build as accessing the mounted volume from a Docker container was around 20 times slower than on Linux :O

perching_aix• 8 months ago

Every FS I've ever had the misfortune of using chokes on lots of small files, especially if they're stored in a flat manner.

atonse3• 8 months ago

I am advising a dev team that's used to using windows to use WSL for the new NextJS app we're building.

But the filesystem performance really put a huge spoke in this. I thought everything was better with WSL2, but I was surprised to see that MS hasn't engineered some driver or something that would make this much more performant or pass-thru so that you can have a directory on windows but also have it perform really well in the VM.

duskwuff• 8 months ago

Actually, there's an interesting question - how does Wine implement (or not implement) Windows API calls which interact with filesystem features which aren't available on Linux, like alternate data streams or complex ACLs?

saghm• 8 months ago

From a quick search, it sounds like ACL metadata is stored in a way that's specific to NTFS. Given that Wine prefixes don't tend to have their own partitions, I'm guessing that if Wine supports them, they just store the info in a config file (similar to how the registry is implemented via text files stored in the root of the prefix) and then looks up accesses from there.

Wine probably isn't something you'd want to use if you're concerned about actually enforcing full Windows security rules. Even if you were able to enforce access to files when executing within Wine itself, the wine prefix will still usually just be a bunch of 644-permissioned files sitting on a Linux filesystem that can get used like any other; the entire wine prefix is just a regular directory with regular files from the external perspective of the wider system, and nothing stops anyone from doing whatever they want that they could do to any other file with the same permissions.

the84722• 8 months ago

wine gets support from the kernel, like case-insensitive directories on ext4.

add-sub-mul-div• 8 months ago

Can you create multiple instances each with their own IP address like you can with Virtualbox? Networking was the reason I didn't stick with WSL2 when I tried it but that was a long time ago and it's probably improved.

Rucadi2• 8 months ago

yes just use brige networking instead of nat

smw• 8 months ago

Strangely, if you create multiple 'instances', they're actually all running as "containers" in the same vm with the same kernel. You can see this by running `wsl --system` and noticing that ps will show you processes from all running wsl distros.

ZhiqiangWang• 8 months ago

The issue I have is VHDX keeps expanding, and you need to manually compact it to claim disk back to host.

andix11• 8 months ago

I think there is an auto shrink feature, but it might cause more trouble than good.

Rucadi2• 8 months ago

cpu 100% and shitty integration.

okanat4• 8 months ago

You need to enable sparse VHD! However it doesn't alwyas trigger. I have moderate success with enabling TRIM systemd service on the distro.

Here is the tracking issue:

https://github.com/microsoft/WSL/issues/12103

And if nothing works you can still manually optimize.

https://superuser.com/questions/1827953/reclaim-wsl2-disk-sp...

9cb14c1ec02• 8 months ago

Tip for all you hackers out there. WSL bypasses windows firewall rules by default. Not sure why Microsoft ever thought that was a good idea.

Demiurge• 8 months ago

Is this, indeed, a fact? I've always had trouble getting ssh to work under WSL.

9cb14c1ec02• 8 months ago

https://github.com/microsoft/WSL/discussions/10579

pjmlp7• 8 months ago

Missed the background info that WSL 1 was a pico process, based on Drawbridge research, and not the same as previous subsystems.

"The Linux Kernel Hidden Inside Windows 10"

https://youtu.be/_p3RtkwstNk?si=V9vhvrdDOLu2Durr

WSL Pico Process Overview

https://learn.microsoft.com/de-de/archive/blogs/wsl/pico-pro...

The same Drawbridge technology is used to run SQL Server on Linux.

https://arstechnica.com/information-technology/2016/12/how-a...

zokier• 8 months ago

The article mentions dynamic memory sizing as one of the benefits of WSL2 over traditional VMs, but afaik Hyper-V supports that on normal Linux VMs too. WSLg is genuinely pretty nifty, but for command-line stuff WSL2 imho doesn't really bring that many advantages.

finaard5• 8 months ago

While I understand _why_ they did WSL2 it's pretty sad that they at the same time they just dropped any WSL1 development.

We're using a lot of WSL in CI - we're mostly Linux based, but for some stuff toolchains came up which didn't work nicely with wine (like MSVC). So for us we want a Linux system that seamlessly can execute Windows stuff in a Linux based build process. WSL1 can do that, WSL2 can be kicked into working somewhat, but needs quite a few ugly workaround as they're not sharing a process namespace or file descriptors. While the faster IO would be nice that's pretty much the only thing we'd care about - and wouldn't work here, as we need shared access to the files. And while we could access the WSL2 files from Windows side that's even slower than just using WSL1.

awestroke• 8 months ago

Windows files are still available via /mnt/c on WSL2

finaard5• 8 months ago

As WSL1 runs on the same kernel I have stuff like named pipes available. I can fully mix processes from both worlds in one workflow. _Some_ of that works with WSL2 as well, but as it's processes on two different kernels requires hidden workarounds to make that work - and not everything is working (and may be even possible).

Intralexical• 8 months ago

For MSVC, have you explored using clang-cl as a drop-in replacement?

https://clang.llvm.org/docs/MSVCCompatibility.html

https://llvm.org/devmtg/2014-04/PDFs/Talks/clang-cl.pdf

XWin for the CRT/SDK:

https://github.com/Jake-Shadle/xwin

https://jake-shadle.github.io/xwin/

A while ago I got some Python C extension modules building using this approach, but didn't push it any further.

finaard5• 8 months ago

That'd mean we have a different compiler in CI than what the developers use on their workstations - which is not a good thing. And wouldn't be tolerated there anyway - people already had some doubts when we were wrapping IAR with wine and a bit of shell to look like a standard UNIX toolchain.

(Shout-out to IAR, though. I still think they're overpriced and you don't really need them - but if you're stuck with them their support is excellent. When an update broke license handling in our setup they didn't tell us to go away like any other vendor would've done for that kind of wildly unsupported use case, but actually made it work again in the next release. They also got us access to native Linux binaries way before they even were talking in public about working on that to play around with for our CI)

jesuslop• 8 months ago

Could one mount a real coexisting ext4 partition to reduce some of the perf penalty of having to simulate a block device on top of those ugly big image files?

CivBase2• 8 months ago

WSL1 felt like a useful compatibility layer for running some Linux applications in Windows. It had plenty of warts, but it quickly became my preferred command shell for Windows.

WSL2 is more capable, but it's not Windows anymore. I might as well run a proper Linux VM or dual boot. Better yet, I'd rather run a Windows VM in a bare metal Linux OS. Why even bother with WSL2? What's the value add?

EgoIncarnate• 8 months ago

Vs WSL1:

GPU access. Actual graphics use is so so, but essential for doing CUDA/AI stuff

Faster file system access on the Linux side (for Linux compiles etc). Ironically, accessing Windows filesystem is slower than WSL1.

Better Linux compatibility.

Vs a Linux VM:

GPU access!

Easier testing for localhost stuff, Linux ports get autoforwarded to Windows (if your test http server is running in WSL2 at port 8080, you can browse to http://localhost:8080 in your Windows browser)

Easy Windows filesystem interaction. Windows local drives show up in /mnt automatically.

Mix Windows commands with Linux commands. I use this for example to pipe strings.exe, which is UTF-16 aware, with Linux text utils.

I think WSL2 tends to be better at sharing memory (releasing unused memory) with the rest of the system than a dedicated VM.

You can mimic some of this stuff to a degree with a VM, but the built in convenience facetor can't be overlooked, and if you are doing CUDA stuff there isn't a good alternative that I am aware of. You could do PCI passthrough using datacenter class GPUs and Windows Server, but $$$.

FergusArgyll• 8 months ago

Full access to the windows filesystem

You can call windows programs from linux (e.g. explorer.exe .)

dboreham2• 8 months ago

I might as well run a proper Linux VM or dual boot.

Obviously you don't do the thing you're writing about. A "proper" Linux VM would incur more work for you and would be less useful. Dual boot would remove your ability to use the computer for activities that need a Windows OS. Running a Windows VM on Linux would take you down a rabbit hole of pain and annoyances, unless your use case for Windows is extremely limited.

CivBase2• 8 months ago

I dual boot, but I avoid Windows as much as possible.

eirikbakke• 8 months ago

I concur. This was my main experience with WSL1 vs. WSL2.

If I'm running Windows, it means that the files and projects that I care about are on the Windows file system. And they need to be there, because my IDE and other GUI apps needs files to be on a real file system to work optimally. (A network share to a WSL2 file system would not let the IDE watch for changes, for instance.)

WSL1 was a great way to get a UNIX-style command line, with git, bash, latex etc., for the Windows file system. WSL2 was just too slow for this purpose; commands like "git status" would take multiple seconds on a large codebase.

Now I switched back to MacOS, and the proper UNIX terminal is a great advantage.

Pannoniae• 8 months ago

"1.6GB on a 32GB system. [...] I think that's pretty much okay. What'a a gigabyte to spare in these days anyway? Just assume that you're running your clock app under Electron."

LOL, this made my day :P

morshu9001• 8 months ago

My limited and nontechnical experience with WSL2 is that it quacks like a subsystem. Great article though.

DeathArrow• 8 months ago

Who remembers Cooperative Linux or coLinux?

http://www.colinux.org/

rzzzt• 8 months ago

HN remembers: https://news.ycombinator.com/item?id=42989923

cachius• 8 months ago

Also one of LBW, LINE or LOW?

LBW is a Linux system call translator for Windows. It allows you to run unmodified Linux applications on top of Windows.

It is not virtualisation; only one operating system is running, which is Windows. It is not emulation; Linux applications run directly on the processor, resulting in (theoretically) full native performance.

Consider it as being like WINE, but in reverse.

https://cowlark.com/lbw/index.html https://github.com/davidgiven/LBW

LINE Is Not an Emulator. LINE executes unmodified Linux applications on Windows 98/2000 by intercepting Linux system calls. The Linux applications themselves are not emulated. They run directly on the CPU like all other Windows applications.

LINE runs best on Windows 2000

https://web.archive.org/web/20010803130404/http://line.sourc...

Call me crazy, but I've wanted to run a linux binary natively under windows for a while now; kinda like wine, but in reverse.

Well, the other day I was browsing through the MSDN docs (as you do) and discovered that it is possible to install a "vectored" exception handler. A quick bit of test code later, and I discovered that I can trap "int 0x80" instructions using this technique--those are used by linux binaries to initiate syscalls

https://web.archive.org/web/20100409222341/http://netevil.or...

kevinmgranger• 8 months ago

I keep reading that WSL2 uses 9p, but that's not _exposed_ anywhere, right?

shmerl4• 8 months ago

What's a good way to have Linux VM with graphics acceleration on Windows host? WSL doesn't cut it and VirtualBox has really broken graphics support.

tuetuopay2• 8 months ago

I’ve found VMware to work well, though it’s degrading quickly. X11 is sorta broken, and not all Wayland compositors run.

As an example, I can run KiCAD just fine under X11 with the modesetting driver, including the 3D board view.

shmerl4• 8 months ago

I need something that can run KDE Wayland session properly, including clipboard sync. VirtualBox has a broken clipboard (supposedly they plan to fix it), and it's only software rendering.

How does VMware implement OpenGL and Vulkan acceleration in the VM?

okanat4• 8 months ago

WSL supports a kernel-based DirectX to Mesa bridge. It is better than any other VM implementation. However the latest releases caused some problems with auto detection mechanism in Mesa. Sometimes the Linux kernel module also fails to load.

You need to ensure that DirectX driver is used with tools like eglinfo. Most of the time, the main culprit is LLVMpipe software driver being used due to wrong detection.

shmerl4• 8 months ago

You can't run a proper VM there though, something like a normal distro with systemd, KDE Wayland session and etc. At least from what I've figured out so far. Basically I need a normal full featured VM, not some gimped variant and with graphics acceleration preferably.

Const-me• 8 months ago

I find WSL 1 incredibly useful. C++ and .NET compiler toolchains, ssh and scp clients, and many other command-line Linux tools are working flawlessly for me despite the fake emulated kernel lacking some of the APIs. When I develop anything related to Linux be it embedded or servers, I use WSL1 a lot.

I find WSL2 pretty much useless. When I want Linux inside a VM I use VMware which is just better. VMware has tree of snapshots to rollback disk state, hardware accelerated 3D graphics (limited though, I think only GL is there no Vulkan, but it’s better than nothing), can attach complete USB devices to the guest OS, can setup proper virtual networks with multiple VMs, and the GUI to do all that is decent, no command line required.

mshroyer• 8 months ago

Some distros have better WSL support than others—some will only work with systemd disabled, others have issues with X11. Ubuntu is well supported of course, but on the RHEL-ish side I've found that AlmaLinux 10 works especially well.

Isn't WSL2 just a VM?

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