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

# 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
pcie_aspm=off	Prevent PCIe conflicts with the T2 bridge
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	10	ZRAM is 15.4 GB — prefer keeping data in RAM
vm.vfs_cache_pressure	50	Retain filesystem cache longer
vm.dirty_writeback_centisecs	6000	Reduce NVMe write frequency for BTRFS
vm.dirty_expire_centisecs	6000	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: set to default (disabled globally via kernel cmdline)

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 and starts a background defragmentation of /home.

Recommended fstab options:

noatime,compress=zstd:1,space_cache=v2,autodefrag,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.

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.