System Optimisation

The 03-optimise.sh script applies post-install optimisations specific to the MacBook Air 2020 running CachyOS. It can be run as root for full system tuning, or as a normal user for audio-only configuration.

Running

The optimisation script is now included in the unified interactive installer. You can run everything at once with:

make install

If you prefer to run it individually:

# Full optimisation (kernel, TLP, BTRFS, sleep, packages)
sudo bash scripts/03-optimise.sh

# Audio fix only (no root required)
bash scripts/03-optimise.sh --audio-only
systemctl --user restart pipewire pipewire-pulse

What the Script Does

1. Kernel Parameters

Adds the following to /etc/kernel/cmdline (read by limine-entry-tool):

Parameter	Purpose
intel_idle.max_cstate=4	Allow efficient C-states while avoiding audio pops
snd_hda_intel.power_save=0	Disable HDA power save for T2 audio stability
mem_sleep_default=deep	Use deep sleep (S3-equivalent) by default

Limine integration

Do not edit /boot/limine.conf directly. The script updates /etc/kernel/cmdline and limine-entry-tool regenerates boot entries automatically on kernel updates.

2. sysctl Tuning

Writes /etc/sysctl.d/99-macbook-air-2020.conf:

Setting	Value	Rationale
vm.swappiness	133	ZRAM is 15.4 GB — high value maximises compressed-RAM utilisation
vm.vfs_cache_pressure	50	Retain filesystem cache longer
vm.dirty_writeback_centisecs	1500	Balance NVMe wear with responsiveness for BTRFS
vm.dirty_expire_centisecs	1500	Match writeback interval
net.core.netdev_max_backlog	4096	Network performance
net.ipv4.tcp_fastopen	3	Enable TCP Fast Open (client + server)
kernel.nmi_watchdog	0	Reduce overhead (nowatchdog already in cmdline)

3. TLP Power Management

Writes /etc/tlp.d/10-macbook-air-2020.conf with Ice Lake-specific settings:

• CPU governor: performance on AC, powersave on battery
• CPU boost: enabled on AC, disabled on battery
• Wi-Fi power management: disabled (BCM4377b disconnects under power management)
• USB autosuspend: disabled (USB_AUTOSUSPEND=0) for T2 BCE bridge stability
• Sound power save: disabled on both AC and battery (prevents T2 audio crackling)
• PCIe ASPM: default on AC, powersupersave on battery (managed per-device by TLP for 10-15% battery savings)

4. PipeWire Audio Fix

Writes ~/.config/pipewire/pipewire.conf.d/10-t2-macbook-audio.conf:

context.properties = {
    default.clock.rate          = 48000
    default.clock.quantum       = 1024
    default.clock.min-quantum   = 256
    default.clock.max-quantum   = 2048
}

This increases the audio buffer to prevent xruns (crackling/pops) on the apple-bce audio path. The minimum quantum is 256 frames, not 1024 — this allows low-latency applications to request smaller buffers when needed.

5. BTRFS Mount Options

The script displays recommended mount options for /etc/fstab but does not edit fstab automatically (too risky). It applies noatime live via mount -o remount.

Recommended fstab options:

noatime,compress=zstd:1,space_cache=v2,discard=async

The root UUID is detected automatically via findmnt.

6. Suspend / Resume Fix

Installs /etc/systemd/system/macbook-suspend-fix.service:

• Runs on every resume from suspend
• Reloads the apple-bce module to restore keyboard/trackpad if they freeze after wake

WARNING

The service only reloads apple-bce. Wi-Fi (brcmfmac) is not reloaded by this service — it generally survives suspend without issues.

7. ZRAM Verification

Confirms that ZRAM is correctly configured (15.4 GB, zstd compression). No changes are made — CachyOS configures this during installation.

8. Power Profiles Daemon

Checks whether both TLP and power-profiles-daemon are active. If both are running, the script warns about the conflict and shows the commands to disable one or the other. It does not disable either service automatically — this is a manual decision.

9. Intel i915 GUC/HUC

Enables GPU firmware offloading by writing options i915 enable_guc=3 enable_fbc=1 to /etc/modprobe.d/i915.conf. This offloads GuC (command submission) and HuC (video decode) to the GPU's own firmware, reducing CPU overhead on the Ice Lake Iris Plus.

10. RTC UTC Clock Sync

Sets the hardware clock to UTC via timedatectl set-local-rtc 0. This ensures correct time handling when dual-booting with macOS, which also expects UTC on modern versions.

Execution Model

The script has two execution paths:

Invocation	Sections Run
sudo bash 03-optimise.sh	Kernel params, sysctl, TLP, BTRFS, sleep, packages, ZRAM check, power profiles, then calls --audio-only as $SUDO_USER
bash 03-optimise.sh --audio-only	PipeWire audio config only (user-level, no root)

Running without sudo applies only the audio fix, ZRAM check, and power profiles check.