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docs(deploy): document CPU isolation in performance-tuning section

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Explains the core-0-vs-game-cores split, the LEFT4ME_SYSTEM_CPUS /
LEFT4ME_GAME_CPUS overrides, the single-core skip, and the
subset-of relationship with per-instance CPUAffinity=.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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mwiegand 2026-05-09 11:06:59 +02:00
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deploy/README.md
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@ -90,6 +90,20 @@ Install via `sudo apt install linux-cpupower` if the binary isn't present.
Persist via your distro's CPU-frequency tooling (e.g. `/etc/default/cpufrequtils`). Persist via your distro's CPU-frequency tooling (e.g. `/etc/default/cpufrequtils`).
### CPU isolation (cores)
The deploy script writes four `AllowedCPUs=` drop-ins so that, by default, only `l4d2-game.slice` is allowed to run on cores 1..N-1; `system.slice`, `user.slice`, and `l4d2-build.slice` are pinned to core 0. Game servers thus get the host minus core 0 exclusively, the build sandbox and the web app stay on core 0, and a logged-in admin running CPU-heavy work in their shell can't steal cycles from a live match.
Override the split by setting either env var when running the deploy:
```sh
LEFT4ME_SYSTEM_CPUS="0,1" LEFT4ME_GAME_CPUS="2-7" deploy/deploy-test-server.sh deploy-user@host
```
On single-core hosts the deploy skips the cpuset drop-ins entirely and prints a warning to stderr; the rest of the perf baseline (cgroup weights, sysctls, OOM scores) still applies. To force isolation on a single-core host anyway (rarely useful), set either env var explicitly.
Per-instance `CPUAffinity=` (next subsection) composes on top of this — the per-instance value must be a subset of `l4d2-game.slice`'s `AllowedCPUs=`, which the kernel enforces.
### Per-instance CPU affinity ### Per-instance CPU affinity
`srcds` is single-threaded per instance. On a multi-core host, pinning each instance to its own core can cut jitter under contention. Drop in `/etc/systemd/system/left4me-server@<name>.service.d/affinity.conf`: `srcds` is single-threaded per instance. On a multi-core host, pinning each instance to its own core can cut jitter under contention. Drop in `/etc/systemd/system/left4me-server@<name>.service.d/affinity.conf`: