information for realtime stuff.py

## Make sure the kernel in use has a real time patch available for it.
## Check the below patch site for a patch for the appropriate kernel

## For gentoo, its usually necessary to emerge a specific version of the kernel as not all version have a patch set
## Using different kernel than the one you're using also allows you to switch between a working version if something goes wrong
## You need to make sure the exact version matches, example: 5.15.65 is exact version I used

## Patch site
## https://cdn.kernel.org/pub/linux/kernel/projects/rt/5.15/


## Emerge new kernel
## most likely have to unmask the specific version to match the real time patches

## example
echo "sys-kernel/gentoo-sources:5.15.65" >> /etc/portage/package.accept_keywords/gentoo-sources-5.15.65

## emerge the specified sources you want to patch
emerge -av gentoo-sources:5.15.65  

## set kernel to the new version
eselect kernel list 
eselect kernel set # 

## change directory to the select kernel sources
cd /usr/src/linux

## Download the patch and place it in your /usr/src/linux directory
## this is the specific version for 5.15.65 and place it in your /usr/src/linux directory
wget https://cdn.kernel.org/pub/linux/kernel/projects/rt/5.15/patches-5.15.65-rt49.tar.gz

## copy over the old .config 
## I recommend making a backup of the .config of your old working kernel BEFORE you patch and update the .config
cp /usr/src/<old version>/.config /usr/src/linux/.config

## download single patch and use the following command to patch it
zcat patches-5.15.65-rt49.tar.gz | patch -p1 

## cd to kernel source dir and update the .config
## this will prompt with the new changes, if you're updating to a minor version there will really only be like 3 options
## if your moving to a different major version like from 5.15 to 5.19, then there will be a lot more options.
make olddefconfig

## compile the kernel
## set '24' to be the amount of jobs you want to spawn when compiling, my pc has lots of cores
make -j 24 && make modules_install && make install

## create new initramfs -- I use dracut but you could use genkernel too
dracut --hostonly --kver 5.15.65-gentoo-rt 

## Update Grub (I use grub) or whatever you use
grub-mkconfig -o /boot/grub/grub.cfg

## recompile the nvidia drivers with a specific flag set to allow realtime kernel. Otherwise nvidia drivers fail
IGNORE_PREEMPT_RT_PRESENCE=1 emerge -av nvidia-drivers

## Portage can be configured to set this environment variable everytime you compile the nvidia-drivers using package.env
## First make the following directories as they aren't created by default on the system
mkdir /etc/portage/{package.env, env}

## add the following to /etc/portage/env/nvidia-drivers.config
IGNORE_PREEMPT_RT_PRESENCE=1

## add the following to /etc/portage/package.env/nvidia-drivers
echo "x11-drivers/nvidia-drivers nvidia-drivers.conf" >> /etc/portage/package.env/nvidia-drivers

## When you emerge nvidia-drivers in the future it will have the IGNORE_PREEMPT_RT_PRESENCE variable set. 
## Sadly it doesn't look like there is a way to see this variable with emerge --info nvidia-drivers, but it does seem to work.

## Reboot and select new kernel