Nix Profiling - Revision history

Justus at 07:11, 3 March 2026

2026-03-03T07:11:36Z

← Older revision		Revision as of 07:11, 3 March 2026
Line 14:		Line 14:
	$ flamegraph < nix.profile > nix.svg		$ flamegraph < nix.profile > nix.svg
	</pre>On my system, this creates a 3.5 MiB SVG file.		</pre>On my system, this creates a 3.5 MiB SVG file.

			=== home-manager fonts ===
			<code>darwin/fonts.nix</code> curiously becomes part of a long call chain here. I've always wondered why that happens. Here's the source code of <code>darwin/fonts.nix</code>:<pre>
			# https://github.com/nix-community/home-manager/blob/2b9504d5a0169d4940a312abe2df2c5658db8de9/modules/targets/darwin/fonts.nix
			# SPDX-FileCopyrightText: 2017-2026 Home Manager contributors
			# SPDX-License-Identifier: MIT
			{
			config,
			lib,
			pkgs,
			...
			}:

			let
			homeDir = config.home.homeDirectory;
			fontsEnv = pkgs.buildEnv {
			name = "home-manager-fonts";
			paths = config.home.packages;
			pathsToLink = [ "/share/fonts" ];
			};
			fonts = "${fontsEnv}/share/fonts";
			installDir = "${homeDir}/Library/Fonts/HomeManager";
			in
			{
			# macOS won't recognize symlinked fonts
			config = lib.mkIf pkgs.stdenv.hostPlatform.isDarwin {
			home.file."Library/Fonts/.home-manager-fonts-version" = {
			text = "${fontsEnv}";
			onChange = ''
			run mkdir -p ${lib.escapeShellArg installDir}
			run ${pkgs.rsync}/bin/rsync $VERBOSE_ARG -acL --chmod=u+w --delete \
			${lib.escapeShellArgs [
			"${fonts}/"
			installDir
			]}
			'';
			};
			};
			}
			</pre>Specifically line 26 takes a long time to finish:<pre>
			${lib.escapeShellArgs [ "${fonts}/" installDir ]}
			</pre>Going further up in the call chain, I can see that this is part of the home manager activation script generation. To resolve <code>"${fonts}"</code>, you need to compute <code>config.home.packages</code>. That's why, coincidentally, creating the <code>.home-manager-fonts-version</code> file resolves all packages.

Justus: /* Nix-darwin */

2026-03-03T06:34:17Z

Nix-darwin

@@ Line 4: / Line 4: @@
 # after your hostname
 nix eval --option eval-profiler flamegraph .#darwinConfigurations.$(hostname).system
 </pre>

Justus: Create page

2026-03-03T06:19:25Z

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== Nix-darwin ==
First, run the following to get a flamegraph:<pre>
# This assumes that you've named your nix-darwin configuration
# after your hostname
nix eval --option eval-profiler flamegraph .#darwinConfigurations.$(hostname).system
</pre>