Real-time version PREEMPT_RT

[4-FLOSS-Free-Libre-Open-Source-Software]

Since mainline Linux Kernel 6.12 ships, PREEMPT_RT. No patching required anymore for real time kernel.

https://xanmod.org lists alongside LTS that we got already here, another branch

RT	Stable Real-time

Well the Xanmod is not 6.12 yet and the RT version equals LTS and is 6.6 currently.

A Locietta/xanmod-kernel-WSL2 fork, implemented it:
taalojarvi@fe4ee5e

Can we add another release, additional to LTS for RT version?

[Andarwinux]

I doubt RT makes sense for WSL, no one is trying to use WSL2 as a pro-audio workstation or an IoT edge controller, and for other general use cases it just reduces performance.

By the way, if you enable RT, you will lose THP.

ref:
https://lwn.net/Articles/938236
https://www.youtube.com/watch?v=7hwoJanE5-U

[4-FLOSS-Free-Libre-Open-Source-Software]

By the way, if you enable RT, you will lose THP.

Thanks for hint, it also disables more flags according to Disabled CONFIG_ options, but which should not affect this WSL2 Kernel version negatively further than lacking THP for now, until THP realtime support fixed.

Several features are disabled by CONFIG_PREEMPT_RT=y because of incompatibility.

Disable Incompatible Options with PREEMPT_RT:

• CONFIG_TRANSPARENT_HUGEPAGE: transparent huge page (THP) support; currently, it is disabled when PREEMPT_RT is chosen. Gleixner said that the problems with THP for realtime need to be fixed, "patches welcome". The realtime project has been focused on getting other things done, and has not tackled THP yet. There is no technical reason why the two cannot work together, they just do not right now.

[taalojarvi]

Since mainline Linux Kernel 6.12 ships PREEMPT_RT. No patcing required anymore for real time kernel.

https://xanmod.org lists alongside LTS that we got already here, another branch
RT Stable Real-time

Well the Xanmod is not 6.12 yet and the RT version equals LTS and is 6.6 currently.

An Locietta/xanmod-kernel-WSL2 fork, implemented it: taalojarvi@fe4ee5e

Can we add another release, additional to LTS for RT version?

Would it be a good idea to move from PREEMPT_VOLUNTARY to PREEMPT?

[4-FLOSS-Free-Libre-Open-Source-Software]

I was testing this. Changes were pushed out of source. Apart from scheduler latency being very consistent, there wasn't any notable improvements.

But you were testing an < 6.12 Kernel Version or?

[Andarwinux]

xanmod-kernel-WSL2/.github/workflows/build.yml

Line 59 in 2b260b0

export VERSION_BRANCH=$(curl -s https://xanmod.org/ -A $CURL_UA | awk '/MAIN/{getline; getline; print}' | grep -oP '[0-9]+\.[0-9]+')

You need to change this to EDGE to switch to 6.12.

[Locietta]

Would it be a good idea to move from PREEMPT_VOLUNTARY to PREEMPT?

How much do we care latency on WSL2? PREEMPT_NONE->PREEMPT_VOLUNTARY ->PREEMPT->PREEMPT_RT gradually trade throughput for lower system latency. Despite wslg exists, I think most use cases of WSL are still about CLI and computing, much like a linux server, that's probably why official kernel sticks with PREEMPT_NONE.

That said, switching to PREEMPT_DYNAMIC might be a good compromise. Users can just override preempt strategy to none/voluntary/full by passing kernel cmdline with .wslconfig if they want.

[4-FLOSS-Free-Libre-Open-Source-Software]

Even today rt cannot be selected with the PREEMPT_DYNAMIC boot parameter.
PREEMPT_RT would still be a separate compile time option

Ensure that PREEMPT_DYNAMIC is enabled in the kernel, possible values for the preempt parameter are:

To enable the voluntary preemption mode (PREEMPT_VOLUNTARY):

[wsl2]
kernelCommandLine = preempt=voluntary

To enable the desktop preemption mode (PREEMPT_DESKTOP):

[wsl2]
kernelCommandLine = preempt=full

To disable preemption (PREEMPT_NONE):

[wsl2]
kernelCommandLine = preempt=none

[Andarwinux]

Let's wait for PREEMPT_LAZY in 6.13, for now PREEMPT_DYNAMIC is good enough.

[4-FLOSS-Free-Libre-Open-Source-Software]

xanmod-kernel-WSL2/.github/workflows/build.yml

Line 59 in 2b260b0

export VERSION_BRANCH=$(curl -s https://xanmod.org/ -A $CURL_UA | awk '/MAIN/{getline; getline; print}' | grep -oP '[0-9]+\.[0-9]+')

You need to change this to EDGE to switch to 6.12.

Now it's the stable Branch >6.12

https://github.com/Locietta/xanmod-kernel-WSL2/releases/tag/6.12.5-locietta-WSL2-xanmod1.1

Will there be a real-time CONFIG_PREEMPT_RT enabled xanmod kernel build for wsl2?

[Andarwinux]

You can build your own toy kernel, but CI resources shouldn't be wasted on a meme, especially since we already provide three variants: do we need to build six?

[4-FLOSS-Free-Libre-Open-Source-Software]

since we already provide three variants: do we need to build six?

This is called Xanmod and Xanmod ships as

1. Main. V1,V2,v3
2. LTS V1,V2, V3
3. RT V2,V3

[4-FLOSS-Free-Libre-Open-Source-Software]

Let's wait for PREEMPT_LAZY in 6.13, for now PREEMPT_DYNAMIC is good enough.

What waiting for? This kernel is currently in version 6.13.8.

If PREEMPT_DYNAMIC is good enough for your random workload, then this issue is not for you.

This issue is about the missing realtime Kernel flavor. Since this is called xanmod and xanmod long time had patches for realtime Kernel. Now we got realtime in mainline kernel, just need to make use of it by enabling that flag.
If there could be compromise in performance, then this should be a different kernel image.
Just like xanmod shipped it's

[4-FLOSS-Free-Libre-Open-Source-Software]

How much do we care latency on WSL2? PREEMPT_NONE->PREEMPT_VOLUNTARY ->PREEMPT->PREEMPT_RT gradually trade throughput for lower system latency.

Since mainline Linux kernels (from 6.12 onward) offer PREEMPT_RT without additional patching, enabling a dedicated real-time kernel flavor can deliver consistently low scheduler latency even if it sacrifices some throughput (e.g., disabling THP) compared to non‑real-time variants. This flag justifies its inclusion for users who need predictable performance in latency-critical workloads.