From c385cd3713db854f47d903d01d17263f8320b134 Mon Sep 17 00:00:00 2001
From: rope <fredrik@nordhammer.it>
Date: Sun, 9 Aug 2026 09:07:59 +0100
Subject: [PATCH] macbook: drop nom, store auto-optimise, halve substitution
 jobs

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
---
 common.nix               | 17 +++++++++++++++--
 hosts/FredOS-Macbook.nix |  4 +++-
 2 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/common.nix b/common.nix
index 229139e..6330900 100644
--- a/common.nix
+++ b/common.nix
@@ -1,6 +1,15 @@
 # Common.nix
 { config, pkgs, lib, inputs, ... }:
 
+let
+  isMacbook = config.networking.hostName == "FredOS-Macbook";
+
+  # nom's Haskell renderer measured 91% CPU during a rebuild — a full core of
+  # the Macbook's four, spent drawing a progress tree, while nix itself wanted
+  # 146%. Plain `-L` output there; the other hosts can afford the pretty one.
+  buildLog = lib.optionalString (!isMacbook)
+    " --log-format internal-json 2>&1 | nom --json";
+in
 {
   imports = [
     # Host modules are imported per-host by mkHost in flake.nix.
@@ -111,7 +120,7 @@
 
   # Shell aliases (work in both bash and fish)
   environment.shellAliases = {
-    update = "bash -c 'set -o pipefail && OLD_SYSTEM=$(readlink /run/current-system) && sudo nixos-rebuild switch $@ --refresh --flake git+https://forg.gregersen.it/rope/nixos -L --log-format internal-json 2>&1 | nom --json && nvd diff $OLD_SYSTEM /run/current-system && (command -v record-update &>/dev/null && record-update $OLD_SYSTEM /run/current-system || true)' --";
+    update = "bash -c 'set -o pipefail && OLD_SYSTEM=$(readlink /run/current-system) && sudo nixos-rebuild switch $@ --refresh --flake git+https://forg.gregersen.it/rope/nixos -L${buildLog} && nvd diff $OLD_SYSTEM /run/current-system && (command -v record-update &>/dev/null && record-update $OLD_SYSTEM /run/current-system || true)' --";
     clean = "sudo nix-collect-garbage -d";
     ll = "ls -alh";
     clear = "command clear";
@@ -131,7 +140,11 @@
 
   # Hard-link identical files in the store as new paths are added, so the
   # store de-duplicates itself on every build instead of drifting.
-  nix.settings.auto-optimise-store = true;
+  # Off on the Macbook: it hashes and relinks every file the daemon writes,
+  # which lands on top of the substitution writes on a slow SATA blade —
+  # measured io pressure full avg60=57% during a rebuild. Run `nix store
+  # optimise` by hand there if the store ever gets fat.
+  nix.settings.auto-optimise-store = !isMacbook;
 
   # Offload builds to the media server. Excluded on the server itself to
   # avoid a pointless SSH round-trip to localhost.
diff --git a/hosts/FredOS-Macbook.nix b/hosts/FredOS-Macbook.nix
index de069cc..55e74f5 100644
--- a/hosts/FredOS-Macbook.nix
+++ b/hosts/FredOS-Macbook.nix
@@ -25,7 +25,9 @@
     # out-of-tree broadcom_sta (wl) driver drops association mid-build —
     # only a manual wifi reconnect brings it back. Cap the concurrency.
     nix.settings.http-connections = 8;
-    nix.settings.max-substitution-jobs = 4;
+    # 2, not 4: each job is an xz/zstd decompress, and there are only 4 threads
+    # to share with the desktop. 4 just queues them behind each other.
+    nix.settings.max-substitution-jobs = 2;
 
     services.tlp.enable = false;
     services.power-profiles-daemon.enable = true;