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docs: wrap up Ralph report (10.87s -> 6.99s = -35.7%)
7 dead-ends documented so they don't have to be re-tried. Key finding: after dropping nixvim (cycle 1), the eval floor is home-manager's per-entry submodule materialisation (systemd.user.services / programs.ssh.matchBlocks), not the option-declaration count of any wrapper module. Inlining jumphost-nix or vira moves the cost; it does not eliminate it.
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Sridhar Ratnakumar
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1 changed files with 134 additions and 2 deletions
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@ -116,11 +116,143 @@ boilerplate itself isn't a contributor.
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| 0 | — | baseline | 10.87 | — | — | reference |
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| 1 | nixvim is 36 % of eval; the cost is the option system, not the resulting nvim binary | delete `inputs.nixvim` + the nixvim module; replace `modules/home/editors/neovim/` with a minimal `programs.neovim { enable; defaultEditor; vimAlias; viAlias; }` | **6.98** | **−3.89 s (−35.8 %)** | ✅ | 7-run median; range 7.73–6.94 (first-run warm-up jitter). Other configs (`naiveintent`, `infinitude-macos`, `srid@zest`) still eval cleanly. **Behaviour note:** nvim is now plain — none of the previous plugins (rose-pine, telescope, treesitter, lualine, noice, LSP keymaps, nvim-tree, lazygit, outline-nvim, mapleader) survive. User explicitly approved dropping nixvim. |
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| 2a | jumphost-nix module is ~1.5 s | inline `${jumphost-nix}/module.nix` into `juspay.nix` (drop input, hard-code values, drop devbox.nix's port-option read) | 7.03 | +0.05 (noise) | ❌ | The shallow drilldown was misleading (eval-error truncation). The cost moves; it doesn't disappear. Reverted. |
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| 2b | vira HM module is ~1.3 s | inline `inputs.vira.homeManagerModules.vira` into `vira.nix` as direct `systemd.user.services.vira` + `age.secrets` | 6.94 | -0.04 (noise) | ❌ | Same explanation as 2a. Reverted. |
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| 2c | unused flake inputs accumulate cost | drop `llm-agents` (literally only commented-out reference) | 7.01 | +0.02 (noise) | ❌ | Lazy inputs don't contribute. Reverted. |
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| 2d | flake-parts modules add overhead | drop `claude-sandboxed.nix`, `devshell.nix`, `landrun-nix` | 6.91–6.99 | ≤0.06 (noise) | ❌ | Reverted. |
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| 2e | `programs.ssh.matchBlocks` is the systemd-style cost driver | strip `controlpersist.nix` (3 matchBlocks) | 7.00 | +0.01 (noise) | ❌ | matchBlocks aren't the contributor either; the cost is the **per-entry merge** that pureintent has anyway via devbox.nix's `pu-jumphost` etc. Reverted. |
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| 2f | nixos-unified's `autoWire` is overhead | replace with a hand-rolled `flake.nixosConfigurations.pureintent = mkLinuxSystem …` | ERR | — | ❌ | Pureintent itself reaches into `self.nixosModules.default` (created by autoWire), so a useful comparison needs reproducing the auto-wired attrsets first — out of scope. |
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## Final measurement
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7 warm runs, eval-cache disabled, `nixos-rebuild dry-build .#pureintent`,
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on `optimize-eval` HEAD (cycle 1 applied):
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| run | seconds |
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|----:|--------:|
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| 1 | 7.00 |
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| 2 | 7.01 |
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| 3 | 6.94 |
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| 4 | 6.99 |
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| 5 | 6.97 |
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| 6 | 7.01 |
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| 7 | 6.94 |
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**Median: 6.99 s** · range 6.94–7.01 (≈ 1 %).
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| | wall (s) | Δ |
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|---|---:|---:|
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| baseline | 10.87 | — |
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| after cycle 1 | **6.99** | **−3.88 s (−35.7 %)** |
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Three other configurations continue to evaluate cleanly:
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`nixosConfigurations.naiveintent`,
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`darwinConfigurations.infinitude-macos`,
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`homeConfigurations."srid@zest"`.
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## Dead ends
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(none yet)
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All of the following were tried after cycle 1 and produced **no
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measurable improvement** (≤ noise floor). Reported here so they don't
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have to be re-tried.
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- **Inline `${jumphost-nix}/module.nix`** into `juspay.nix`. Replaced the
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152-line work-jump-host module with an equivalent inline
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`programs.ssh.matchBlocks` / `systemd.user.services` /
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`programs.git.includes`. Result: 7.03 s — within noise. Earlier
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drilldown numbers that suggested ~1.5 s of jumphost-nix cost were
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*eval-error truncation* (devbox.nix references
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`programs.jumphost.socks5Proxy.port` and aborted eval before the rest
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of pureintent was processed). The real cost is in the resulting
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submodule materialisation (programs.ssh.matchBlocks, etc.), which is
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the same whether the values arrive via a wrapper module or a literal.
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- **Inline `inputs.vira.homeManagerModules.vira`**. 167-line option
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schema + submodule replaced with a hand-rolled
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`systemd.user.services.vira` and `age.secrets` block.
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Result: 6.94 s — within noise. Same explanation as above.
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- **Inline `inputs.kolu.homeManagerModules.default`**. Similar pattern;
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eval errored when `services.kolu.host` setter outlived the option
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declaration. With downstream-fix, expected zero benefit by the same
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argument.
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- **Prune `inputs.llm-agents`** (only reference was already commented
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out). Result: 7.01 s — within noise.
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- **Drop `modules/flake-parts/claude-sandboxed.nix`** (landrun-nix
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consumer at the flake-parts level). Result: 6.91 s — within noise.
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- **Drop `modules/flake-parts/devshell.nix`** at flake-parts level.
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Result: 6.99 s — within noise.
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- **Drop `landrun-nix` input + `claude-sandboxed.nix`**. Result:
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6.97 s — within noise.
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- **Strip `modules/home/cli/controlpersist.nix`** entirely (3
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`programs.ssh.matchBlocks` entries). Result: 7.00 s — within noise.
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- **Replace `nixos-unified.flakeModules.autoWire`** with a manual
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`flake.nixosConfigurations.pureintent = mkLinuxSystem …` — errors,
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because pureintent's own `default.nix` reaches into
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`self.nixosModules.default` which autoWire is responsible for
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creating. Measuring nixos-unified's residual overhead would require
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reproducing the auto-wired module attrsets by hand; not worth the
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effort given everything else has plateaued.
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## Why we plateau at ~7 s
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After cycle 1, the post-mortem profile (each "drop X" probe is run with
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all *downstream consumers stubbed out* so the measurement isn't
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eval-error-truncated):
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| component | wall when dropped | Δ saved |
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|---|---:|---:|
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| (post-cycle-1 baseline) | 6.99 | — |
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| `vira` HM module | ≈ 5.71 | 1.28 |
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| `kolu` HM module | ≈ 6.49 | 0.50 |
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| jumphost-nix module + body | (cannot measure cleanly; ~1.3 cost is real but inlining gives it back) | — |
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| home CLI modules (tmux, starship, terminal, git, direnv, just, npm, nix-index-database, ttyd) | ≈ 0 each, ≈ 0.4 s cumulative | — |
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| `agenix` (NixOS + HM) | ≈ 0 | — |
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| `claude-code`, `buildMachines`, `incus`, `beszel`, `firefox`, `pipewire` | ≈ 0 each | — |
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The remaining ≈ 4 s is the cost of evaluating nixpkgs `lib`, the NixOS
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module system, home-manager's option universe, and `nixos-unified`'s
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auto-wiring — together they are the irreducible floor for any host that
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uses this flake.
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The HM modules that *are* expensive (vira, kolu, jumphost-nix) cost what
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they cost because their values land in
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`systemd.user.services.<name>` or `programs.ssh.matchBlocks.<name>`,
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each of which forces a per-entry home-manager submodule. Inlining the
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wrapper module doesn't help because the merge is the same on either
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side. The only way to reclaim that time is to (a) drop the service /
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the matchBlock entirely, or (b) write the unit / ssh_config file
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directly via `home.file` / `xdg.configFile` and bypass home-manager's
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own ssh and systemd modules across the whole user — a much larger
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refactor than fit inside this PR's scope.
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## Key findings
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(filled in at wrap-up)
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1. **nixvim is 36 % of pureintent's eval time.** Its
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home-manager-style options module materialises hundreds of plugin
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submodules every eval. Cycle 1 dropped it (user-approved behaviour
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change to plain `programs.neovim`) and reclaimed 3.88 s.
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2. **HM submodule materialisation, not option-declaration count, is the
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driver.** Inlining wrapper modules (jumphost-nix, vira) gives the
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work-saving illusion in shallow probes but no real saving because
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`systemd.user.services` and `programs.ssh.matchBlocks` re-do the
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same submodule work regardless of where their values came from.
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3. **Unused flake inputs cost essentially nothing** at pureintent
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eval-time; flake inputs are lazy and only inputs reached
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transitively from `nixosConfigurations.pureintent` contribute.
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4. **Eval-error-truncated probes look like wins.** Any "drop X" probe
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where a downstream module reads X's option silently shortens the
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eval and lies about its cost. Always validate probes succeed (we
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started checking exit codes after the jumphost-nix dead end).
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## Methodology cost
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- 1 successful commit + push (cycle 1).
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- ≈ 50 probe runs on `srid-nc` over the cycle (3-run medians of dry-build).
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- 1 draft PR open: <https://github.com/srid/nixos-config/pull/117>.
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