Migrating to libglvnd in Gentoo Linux on a laptop with NVIDIA Optimus

In a 2015 post I described how I configured my Gentoo Linux installation to switch between the closed-source NVIDIA driver and the open-source Intel driver on a Clevo W230SS laptop that has NVIDIA Optimus hardware (NVIDIA GeForce GTX 860M GPU plus Intel HD 4600 IGP). I did not want to use Bumblebee, preferring to use only the NVIDIA driver or only the Intel driver, switching between them by running a Bash script then logging out of KDE Plasma and back in again. Basically, the scheme a) swapped the xorg.conf file depending on which driver I wanted to use, and b) used the eselect opengl command to select the applicable OpenGL library. The latest versions of the files in my scheme are listed below if you’re interested (I use LightDM instead of KDM these days, as KDM is no more), otherwise just skip to the section after, titled ‘Migrating to libglvnd’.

Previous scheme using eselect opengl

~/Desktop/Select_NVIDIA_GPU.desktop

[Desktop Entry]
Comment[en_GB]=Run a script to configure your installation to use the NVIDIA GeForce GTX 860M GPU when you restart X Windows
Comment=Run a script to configure your installation to use the NVIDIA GeForce GTX 860M GPU when you restart X Windows
Exec=konsole -e sh /home/fitzcarraldo/nvidia.sh
GenericName[en_GB]=Configure your installation to use the NVIDIA GeForce GTX 860M GPU
GenericName=Configure your installation to use the NVIDIA GeForce GTX 860M GPU
Icon=/home/fitzcarraldo/Pictures/Icons/nvidia_icon.png
MimeType=
Name[en_GB]=NVIDIA GPU
Name=NVIDIA GPU
Path=
StartupNotify=true
Terminal=false
TerminalOptions=\s--noclose
Type=Application
X-DBUS-ServiceName=
X-DBUS-StartupType=none
X-KDE-SubstituteUID=false
X-KDE-Username=fitzcarraldo

~/nvidia.sh

#!/bin/bash
echo
echo "Your installation is currently configured to use the following graphics processor:"
echo
GPU=`eselect opengl list | grep \* | awk '{ print $2 }'`
if [ "$GPU" = "nvidia" ]; then
  echo "NVIDIA GeForce GTX 860M"
  echo
  echo "You do not need to do anything. Please close this window."
elif [ "$GPU" = "xorg-x11" ]; then
  echo "Intel HD 4600 Integrated Graphics Processor"
  echo
  echo "This script will configure your installation to use the NVIDIA GeForce GTX 860M GPU all the time."
  echo
  echo "Enter your own password."
  echo
  sudo eselect opengl set nvidia
# See separate configuration of LightDM for NVIDIA GPU and Intel HD Graphics.
  sudo cp /etc/X11/xorg.conf.nvidia /etc/X11/xorg.conf
  echo
  echo "Now you should logout to restart X Windows."
fi
echo
echo -n "Press ENTER to end: "
read ACKNOWLEDGE

/etc/X11/xorg.conf.nvidia

Section "ServerLayout"
    Identifier     "Layout0"
    Screen      1  "nvidia" 0 0
    Inactive       "intel"
EndSection

Section "Monitor"
    Identifier     "Monitor0"
    Option         "DPMS"
    Option         "DPI" "96 x 96"
EndSection

Section "Device"
    Identifier     "nvidia"
    Driver         "nvidia"
    BusID          "PCI:1:0:0"
EndSection

Section "Device"
    Identifier     "intel"
    Driver         "modesetting"
    BusID          "PCI:0:2:0"
EndSection

Section "Screen"
    Identifier     "nvidia"
    Device         "nvidia"
    Monitor        "Monitor0"
    DefaultDepth    24
    Option         "UseDisplayDevice" "none"
    SubSection     "Display"
        Depth       24
        Virtual     1920 1080
    EndSubSection
EndSection

Section "Screen"
    Identifier     "intel"
    Device         "intel"
    Monitor        "Monitor0"
EndSection

~/Desktop/Select_Intel_HD_Graphics.desktop

[Desktop Entry]
Comment[en_GB]=Run a script to configure your installation to use Intel Integrated Graphics when you restart X Windows
Comment=Run a script to configure your installation to use Intel Integrated Graphics when you restart X Windows
Exec=konsole -e sh /home/fitzcarraldo/intel.sh
GenericName[en_GB]=Configure your installation to use Intel HD Graphics
GenericName=Configure your installation to use Intel HD Graphics
Icon=/home/fitzcarraldo/Pictures/Icons/intel-hd-icon.png
MimeType=
Name[en_GB]=Intel HD Graphics
Name=Intel HD Graphics
Path=
StartupNotify=true
Terminal=false
TerminalOptions=\s--noclose
Type=Application
X-DBUS-ServiceName=
X-DBUS-StartupType=none
X-KDE-SubstituteUID=false
X-KDE-Username=fitzcarraldo

~/intel.sh

#!/bin/bash
echo
echo "Your installation is currently configured to use the following graphics processor:"
echo
GPU=`eselect opengl list | grep \* | awk '{ print $2 }'`
if [ "$GPU" = "xorg-x11" ]; then
  echo "Intel HD 4600 Integrated Graphics Processor"
  echo
  echo "You do not need to do anything. Please close this window."
elif [ "$GPU" = "nvidia" ]; then
  echo "NVIDIA GeForce GTX 860M"
  echo
  echo "This script will configure your installation to use the"
  echo "Intel HD 4600 Integrated Graphics Controller all the time."
  echo
  echo "Enter your own password."
  echo
  sudo eselect opengl set xorg-x11
# See separate configuration of LightDM for Intel HD Graphics and NVIDIA GPU.
  sudo cp /etc/X11/xorg.conf.intel /etc/X11/xorg.conf
  echo
  echo "Now you should logout to restart X Windows."
fi
echo
echo -n "Press ENTER to end: "
read ACKNOWLEDGE

/etc/X11/xorg.conf.intel

Section "Device" 
   Identifier  "Intel Graphics" 
   Driver      "intel" 
   Option      "AccelMethod" "sna" 
   Option      "TearFree" "true" 
EndSection

/etc/X11/xorg.conf.d/20-opengl.conf

Section "Files"
        ModulePath "/usr/lib/xorg/modules"
        ModulePath "/usr/lib64/xorg/modules"
EndSection

/etc/X11/Sessions/plasma (used by LightDM)

#!/bin/bash
#
# Make sure the following is in /etc/lightdm/lightdm.conf
# display-setup-script=/etc/X11/Sessions/plasma
#
GPU=`eselect opengl list | grep \* | awk '{ print $2 }'`
if [ "$GPU" = "nvidia" ]; then
    xrandr --setprovideroutputsource modesetting NVIDIA-0
    xrandr --auto
fi

Migrating to libglvnd

Well, the above scheme worked fine… until the recent decision by the Gentoo Linux developers to drop the app-eselect/eselect-opengl ebuild and switch the x11-base/xorg-server, media-libs/mesa and x11-drivers/nvidia-drivers to using the libglvnd library:

This package is masked and could be removed soon!
The mask comment indicates that this package is scheduled for removal from our package repository.
Please review the mask information below for more details.

Replaced by media-libs/libglvnd. Masked for removal in 30 days. Bug #728286

Affected packages	app-eselect/eselect-opengl

Author/Date		Matt Turner  (2020-08-11 00:00:00 +0000 UTC)

Without the eselect opengl command, my scripts were scuppered. So I decided to bite the bullet and switch to using libglvnd. It turned out not to be difficult, and I took the following steps to migrate:

  1. Deleted the file /etc/X11/xorg.conf
  2. Created the file /etc/X11/xorg.conf.d/01-nvidia-offload.conf containing the following:
    Section "ServerLayout"
        Identifier "layout"
        Option "AllowNVIDIAGPUScreens"
    EndSection
    
  3. Performed the usual ‘emerge -uvDN @world‘ to update and upgrade the relevant packages, which automatically unmerged app-eselect/eselect-opengl

If I had run into trouble with the installed app-eselect/eselect-opengl blocking the upgrade, I could have worked around that by doing the following:

root # emerge -C eselect-opengl
root # emerge -1v nvidia-drivers mesa xorg-server xorg-drivers

I removed all references to the libglvnd USE flag from /etc/portage/make.conf, and the only place libglvnd is declared explicitly now is in the file /etc/portage/package.use/world because I have a multilib installation:

root # grep libglvnd /etc/portage/package.*/*
/etc/portage/package.use/world:>=media-libs/libglvnd-1.3.1 abi_x86_32

The status of the applicable packages in my installation is now as follows:

root # eix -I nvidia-drivers
[I] x11-drivers/nvidia-drivers
     Available versions:  [M]340.108-r1(0/340)^mtd ~390.132-r4(0/390)^mtd 390.138-r1(0/390)^mtd 435.21-r6(0/435)^mtd 440.100-r2(0/440)^mtd 450.57-r1(0/450)^mtd {+X compat (+)driver gtk3 +kms +libglvnd multilib static-libs +tools uvm wayland ABI_MIPS="n32 n64 o32" ABI_RISCV="lp64 lp64d" ABI_S390="32 64" ABI_X86="32 64 x32" KERNEL="FreeBSD linux"}
     Installed versions:  450.57-r1(0/450)^mtd(22:04:56 14/08/20)(X driver kms libglvnd multilib tools wayland -compat -gtk3 -static-libs -uvm ABI_MIPS="-n32 -n64 -o32" ABI_RISCV="-lp64 -lp64d" ABI_S390="-32 -64" ABI_X86="32 64 -x32" KERNEL="linux -FreeBSD")
     Homepage:            https://www.nvidia.com/Download/Find.aspx
     Description:         NVIDIA Accelerated Graphics Driver

root # eix -I mesa
[I] media-libs/mesa
     Available versions:  20.0.8^t ~20.1.4^t ~20.1.5^t ~20.2.0_rc1^t ~20.2.0_rc2^t **9999*l^t {+X +classic d3d9 debug +dri3 +egl +gallium +gbm gles1 +gles2 +libglvnd +llvm lm-sensors opencl osmesa selinux test unwind vaapi valgrind vdpau vulkan vulkan-overlay wayland xa xvmc zink +zstd ABI_MIPS="n32 n64 o32" ABI_RISCV="lp64 lp64d" ABI_S390="32 64" ABI_X86="32 64 x32" KERNEL="linux" VIDEO_CARDS="freedreno i915 i965 intel iris lima nouveau panfrost r100 r200 r300 r600 radeon radeonsi v3d vc4 virgl vivante vmware"}
     Installed versions:  20.0.8^t(22:03:42 14/08/20)(X classic dri3 egl gallium gbm gles2 libglvnd llvm wayland zstd -d3d9 -debug -gles1 -lm-sensors -opencl -osmesa -selinux -test -unwind -vaapi -valgrind -vdpau -vulkan -vulkan-overlay -xa -xvmc ABI_MIPS="-n32 -n64 -o32" ABI_RISCV="-lp64 -lp64d" ABI_S390="-32 -64" ABI_X86="32 64 -x32" KERNEL="linux" VIDEO_CARDS="i965 intel -freedreno -i915 -iris -lima -nouveau -panfrost -r100 -r200 -r300 -r600 -radeon -radeonsi -vc4 -virgl -vivante -vmware")
     Homepage:            https://www.mesa3d.org/ https://mesa.freedesktop.org/
     Description:         OpenGL-like graphic library for Linux

[I] x11-apps/mesa-progs
     Available versions:  8.4.0 **9999*l {egl gles2}
     Installed versions:  8.4.0(13:53:51 02/05/19)(-egl -gles2)
     Homepage:            https://www.mesa3d.org/ https://mesa.freedesktop.org/ https://gitlab.freedesktop.org/mesa/demos
     Description:         Mesa's OpenGL utility and demo programs (glxgears and glxinfo)

Found 2 matches
root # eix -I xorg-server
[I] x11-base/xorg-server
     Available versions:  1.20.8-r1(0/1.20.8) **9999(0/9999)*l {debug dmx doc +elogind ipv6 kdrive +libglvnd libressl minimal selinux static-libs suid systemd +udev unwind wayland xcsecurity xephyr xnest xorg xvfb}
     Installed versions:  1.20.8-r1(0/1.20.8)(22:07:21 14/08/20)(elogind ipv6 libglvnd udev wayland xorg -debug -dmx -doc -kdrive -libressl -minimal -selinux -static-libs -suid -systemd -unwind -xcsecurity -xephyr -xnest -xvfb)
     Homepage:            https://www.x.org/wiki/ https://gitlab.freedesktop.org/xorg/xserver/xorg-server
     Description:         X.Org X servers

root # eix -I xorg-drivers
[I] x11-base/xorg-drivers
     Available versions:  1.20-r2 **9999*l {INPUT_DEVICES="elographics evdev joystick libinput synaptics vmmouse void wacom" VIDEO_CARDS="amdgpu ast dummy fbdev freedreno geode glint i915 i965 intel mga nouveau nv nvidia omap qxl r128 radeon radeonsi siliconmotion tegra vc4 vesa via virtualbox vmware"}
     Installed versions:  1.20-r2(22:05:41 14/08/20)(INPUT_DEVICES="evdev synaptics -elographics -joystick -libinput -vmmouse -void -wacom" VIDEO_CARDS="i965 intel nvidia -amdgpu -ast -dummy -fbdev -freedreno -geode -glint -i915 -mga -nouveau -nv -omap -qxl -r128 -radeon -radeonsi -siliconmotion -tegra -vc4 -vesa -via -virtualbox -vmware")
     Homepage:            https://wiki.gentoo.org/wiki/No_homepage
     Description:         Meta package containing deps on all xorg drivers

I can now delete the line display-setup-script=/etc/X11/Sessions/plasma in /etc/lightdm/lightdm.conf, and delete the script /etc/X11/Sessions/plasma, as the script no longer works and the xrandr commands in it are no longer necessary in any case. The files and scripts Select_NVIDIA_GPU.desktop, nvidia.sh, xorg.conf.nvidia, Select_Intel_HD_Graphics.desktop, intel.sh and xorg.conf.intel are also redundant now and can be deleted.

After rebooting, the LightDM login screen appears as usual and I can login to the Desktop Environment. I can connect an external monitor to the laptop via either VGA cable or HDMI cable and both methods work, and I can switch between the laptop monitor and the external monitor using KDE Plasma’s ‘System Settings’ > ‘Display Configuration’, so everything appears to be working correctly.

The command xrandr --listproviders (add ‘--verbose‘ to provide more information) lists both the NVIDIA and Intel video devices, so I assume everything is working correctly:

user $ xrandr --listproviders
Providers: number : 2
Provider 0: id: 0x47 cap: 0xb, Source Output, Sink Output, Sink Offload crtcs: 4 outputs: 4 associated providers: 0 name:Intel
Provider 1: id: 0x203 cap: 0x0 crtcs: 0 outputs: 0 associated providers: 0 name:NVIDIA-G0

It appears that the default is to use the Intel IGP:

user $ glxinfo | grep -E 'OpenGL (vendor|renderer)'
OpenGL vendor string: Intel Open Source Technology Center
OpenGL renderer string: Mesa DRI Intel(R) HD Graphics 4600 (HSW GT2)
user $ __NV_PRIME_RENDER_OFFLOAD_PROVIDER=Intel __GLX_VENDOR_LIBRARY_NAME=mesa glxinfo  | grep -E 'OpenGL (vendor|renderer)'
OpenGL vendor string: Intel Open Source Technology Center
OpenGL renderer string: Mesa DRI Intel(R) HD Graphics 4600 (HSW GT2)

unless I use environment variables explicitly to specify that the NVIDIA GPU be used for a specific application:

user $ __NV_PRIME_RENDER_OFFLOAD_PROVIDER=NVIDIA-G0 __GLX_VENDOR_LIBRARY_NAME=nvidia glxinfo  | grep -E 'OpenGL (vendor|renderer)'
OpenGL vendor string: NVIDIA Corporation
OpenGL renderer string: GeForce GTX 860M/PCIe/SSE2

Performance seems reasonable:

user $ __NV_PRIME_RENDER_OFFLOAD_PROVIDER=NVIDIA-G0 __GLX_VENDOR_LIBRARY_NAME=nvidia __GL_SYNC_TO_VBLANK=0 glxgears
27197 frames in 5.0 seconds = 5439.292 FPS
27332 frames in 5.0 seconds = 5466.274 FPS
27857 frames in 5.0 seconds = 5571.184 FPS
27553 frames in 5.0 seconds = 5510.447 FPS
27128 frames in 5.0 seconds = 5425.556 FPS
^C

To run a program such as LibreCAD using the NVIDIA GPU I can do the following:

user $ __NV_PRIME_RENDER_OFFLOAD_PROVIDER=NVIDIA-G0 __GLX_VENDOR_LIBRARY_NAME=nvidia librecad

I need to play around more to understand how to use nvidia-drivers and libglvnd with the NVIDIA Optimus hardware in this laptop, but at least I have managed to migrate from app-eselect/eselect-opengl to media-libs/libglvnd before the former is dropped from the Portage tree in the near future.

Advertisement

That UPS you bought for your home server may not be as useful as you think

Some years ago I decided to install a server at home for use as a NAS (network-attached storage) in my home network, and for an Internet-facing server. I live in a place where blackouts are very infrequent (perhaps a couple per year), but occasionally the mains drops out for only a second or two. I suspect these very short dropouts occur when substation switchgear operates, but have no way of being sure. Anyway, with a server running 24/7 I obviously wanted protection against any loss of the mains supply.

I ended up buying a 700VA APC Back-UPS ES-BE700G-UK, which has four mains sockets that are battery-backed and also have surge protection, plus another four mains sockets that have surge protection but are not battery-backed. Additionally, it has two RJ45 sockets to provide pass-through filtering for an Ethernet connection. It also has a USB port for connection to the server so that it can transmit unsolicited status information to the server (including requesting the server to shutdown) and can also be interrogated by the server using the apcaccess command. The APC UPS daemon works with this model of UPS, and was relatively easy to set up. APC, formerly American Power Conversion Corporation, is a subsidiary of European company Schneider Electric. My UPS was manufactured in The Philippines.

I have three devices plugged into the battery-backed sockets on the APC UPS: the server, an external 6TB USB HDD connected to the server for automated daily backups by the server, and a 5-port Ethernet switch. The battery in the UPS would provide between 15 and 20 minutes of power when the mains fails, although I have configured the UPS to trigger the server to shutdown when 30 per cent of the battery power remains, as battery life is reduced considerably if its power is allowed to drain completely. In case you’re wondering why my router is not also plugged into the UPS, due to the position of the broadband provider’s socket the router is in a different room and I have therefore had to connect it to a different UPS, an iLEPO multi-functional DC UPS (the ECO PLUS 412P, which is tiny but can keep the router powered for several hours). Obviously the router needs to be connected to a UPS, otherwise the server would not be able to send me e-mails when there is a mains power cut. Being able to receive UPS status e-mails from the server is important to me when I am away from home on work trips.

So I thought I had covered all bases, and, indeed, the UPS proved useful on several occasions. I would quite often be on a work trip and receive an e-mail from the server informing me that mains power to the UPS had been lost, then another e-mail soon after informing me that mains power to the UPS had returned. Only once did the power cut last longer than the battery capacity, and the server was shutdown automatically.

Now, the life of the 12-volt lead-acid battery in the APC UPS is supposed to last approximately three to five years. The life will depend on how many times the battery is discharged and ambient temperature.

While I was away from home on a long work trip, suddenly I could no longer connect to my server and I had not received an e-mail from the server informing me of any problem. Luckily it was near the end of my trip so I was not too inconvenienced. When I arrived home I found that the UPS was sounding an alarm and was not supplying power to the server even though there was mains supply to the UPS. It transpired that the UPS battery had suddenly died without warning and could no longer hold a charge, and this had happened while there was mains supply to the UPS, i.e. there had not been a power cut while I was away. Fortunately there was no loss of data on the server; I was able to run fsck during boot-up.

This failure was annoying on two counts. Firstly, the battery was only about thirteen months old (the manufacturing date stamped on the UPS box was only two or three months before the date I purchased the UPS). Secondly, I certainly did not expect the UPS to stop supplying power to the server while there was mains supply to the UPS. The APC white paper on UPS topologies, ‘The Different Types of UPS Systems‘, does not make this behaviour clear.

It turns out that the type of UPS topology (‘Standby’ — see the model’s Technical Specifications) in this model of UPS does not continue to provide power to connected equipment when the UPS battery either fails or is disconnected for whatever reason when there is mains power supply to the UPS. A quick search of the Web showed me that I was not alone in discovering this ‘feature’: an APC Back-UPS 350 owner posted ‘UPS Battery Backup — useless when the battery dies?‘.

From what I have read, the so-called ‘Line Interactive’ UPS topology does not suffer this shortcoming, so, the next time I have to buy a UPS for a piece of equipment that requires power 24/7, I will buy a line-interactive UPS rather than a standby UPS. But, before purchasing, I will be sure to ask the manufacturer what the precise model would do if its battery fails or is disconnected while there is mains supply to the UPS. The APC line-interactive UPSs are more expensive than the APC Back-UPS models; now I know why. It’s a pity I was not aware of the shortcoming of the Back-UPS models, as I would have spent more and bought a UPS that continues to work when the battery dies while there is mains supply. I would also hope the UPS would issue an alarm if the battery has failed or is disconnected while there is mains supply. Be sure to ask the manufacturer all these questions if you cannot tolerate a sudden loss of power to your equipment if the battery dies while there is mains supply.

Anyway, after checking that the dead battery was indeed useless I replaced it with a new Yuasa battery that has lasted nearly three years now. I will be replacing it shortly as a precaution, even though it has not had to be used much at all since I installed it. I have not replaced the APC Back-UPS model but I will be replacing the battery at least every three years just to be cautious, and of course taking the old batteries to my local waste disposal centre to be recycled properly. By the way, it is possible to purchase a 12-volt battery manufactured by one of the reputable battery manufacturers such as Yuasa with the same specification as the APC battery, for a significantly lower price than APC charges for replacement batteries (which I suspect are badged by APC in any case).

Re-enabling OpenGL compositing automatically after it crashes KWin at login to KDE Plasma

One of my laptops has NVIDIA Optimus hardware and runs Gentoo Linux with the closed-source NVIDIA driver. Almost every time I logged-in to KDE Plasma for the first time after booting, OpenGL and compositing would be disabled (see screenshot below), and the usual methods of toggling compositing on/off would not work.

KDE Plasma - System Settings - Compositor Settings for Desktop Effects

KDE Plasma - System Settings - Compositor Settings for Desktop Effects.

I had to perform the following ritual in order to get ‘wobbly windows’ working again:

  1. select ‘System Settings’ > ‘Display and Monitor’ > ‘Compositor’
  2. click on ‘Re-enable OpenGL detection’
  3. deselect ‘Enable compositor on startup’
  4. click ‘Apply’
  5. select ‘Enable compositor on startup’
  6. click ‘Apply’

After having to perform this tedious process almost every time I logged in to KDE Plasma following boot-up, I finally decided to find an automated method of re-enabling OpenGL detection and compositing. I discovered that, when the problem occurred, the value of the variable OpenGLIsUnsafe in the file ~/.config/kwinrc had become ‘false‘. To get things working again I created the Bash script ~/restart_compositing.sh listed below. The script reverts the value of the variable OpenGLIsUnsafe to ‘true‘, reverts the value of the variable Enabled in the same section to ‘true‘ if it happens to be ‘false‘, and restarts KWin. Simple as that.

#!/bin/bash
#
# OpenGL compositing usually crashes KWin when I login, and compositing is then disabled.
# I have to select 'System Settings' > 'Display and Monitor' > 'Compositor' and perform
# the following steps to get compositing to work in the session:
#
# 1. click 'Re-enable OpenGL detection'
# 2. deselect 'Enable compositor on startup'
# 3. click 'Apply'
# 4. select  'Enable compositor on startup'
# 5. click 'Apply
#
# This script enables me to avoid having to perform the above manual procedure.
# This script is configured to run automatically at Plasma Startup - see:
# 'System Settings' > 'Startup and Shutdown' > 'Autostart'
#
edit_kwinrc () {
                # Extract the [Compositing] section from kwinrc
                awk '/\[Compositing\]/,/^$/' $HOME/.config/kwinrc > /tmp/kwinrc-extract
                # Remove the header in the extracted section
                sed -i '/\[Compositing\]/d' /tmp/kwinrc-extract
                # Remove the empty line at the end of the extracted section
                sed -i '/^$/d' /tmp/kwinrc-extract
                # Change the state configured for next login
                if [ $1 == "disablecompositing" ]; then
                    sed -i 's/Enabled=true/Enabled=false/g' /tmp/kwinrc-extract
                elif [ $1 == "enablecompositing" ]; then
                    sed -i 's/Enabled=false/Enabled=true/g' /tmp/kwinrc-extract
                elif [ $1 == "openglunsafe" ]; then
                    sed -i 's/OpenGLIsUnsafe=false/OpenGLIsUnsafe=true/g' /tmp/kwinrc-extract
                elif [ $1 == "openglsafe" ]; then
                    sed -i 's/OpenGLIsUnsafe=true/OpenGLIsUnsafe=false/g' /tmp/kwinrc-extract
                fi
                # Replace the [Compositing] section in kwinrc
                awk 'BEGIN {p=1} /^\[Compositing\]/ {print;system("cat /tmp/kwinrc-extract");p=0} /^$/ {p=1} p' $HOME/.config/kwinrc > /tmp/kwinrc
                cp /tmp/kwinrc $HOME/.config/kwinrc
}
#
# Avoid backing up an incorrectly-edited file
if [ ! -f $HOME/.config/kwinrc.bak ]; then
    cp $HOME/.config/kwinrc $HOME/.config/kwinrc.bak
fi
#
sleep 120s # This delay works for my specific laptop but might need to be adjusted on other machines.
if $( grep -q "OpenGLIsUnsafe=true" $HOME/.config/kwinrc ); then
    edit_kwinrc openglsafe
    edit_kwinrc enablecompositing # Just in case it was disabled as well.
    kwin_x11 --replace & > /dev/null 2>&1
fi
exit 0

I then selected ‘System Settings’ > ‘Startup and Shutdown’ > ‘Autostart’, clicked on ‘Add Script…’ and specified that /home/fitzcarraldo/restart_compositing.sh has to be run at ‘Startup’ (of Plasma). Problem solved.