94 lines
3.4 KiB
Nix
94 lines
3.4 KiB
Nix
{
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lib,
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pkgs,
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...
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}:
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{
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powerManagement = {
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enable = true;
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powertop.enable = true;
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cpuFreqGovernor = "powersave";
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};
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# Always-on server: disable all sleep targets.
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systemd.targets = {
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sleep.enable = false;
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suspend.enable = false;
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hibernate.enable = false;
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hybrid-sleep.enable = false;
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};
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boot.kernelParams = [
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# Disable NMI watchdog at boot. Eliminates periodic perf-counter interrupts
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# across all cores (~1 W). Safe: apcupsd provides hardware hang detection
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# via UPS, and softlockup watchdog remains active.
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"nmi_watchdog=0"
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# Route kernel work items to already-busy CPUs rather than waking idle ones.
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# Reduces C-state exit frequency at the cost of slightly higher latency on
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# work items -- irrelevant for a server whose latency-sensitive paths are
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# all in userspace (caddy, jellyfin).
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"workqueue.power_efficient=1"
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# Force PCIe ASPM on even if the BIOS doesn't advertise support. ASRock
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# B550M Pro4 BIOS defaults are conservative; the Zen 3 root complex and
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# all downstream devices (NVMe, AHCI, Intel NIC) support L1 substates.
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# powertop auto-tune sets the policy to powersupersave at runtime, but
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# without `force` the kernel may refuse to enable ASPM at all if the BIOS
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# opted out, making the policy write a no-op.
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"pcie_aspm=force"
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];
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boot.kernel.sysctl = {
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# Belt-and-suspenders: also set via boot param, but sysctl ensures it
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# stays off if anything re-enables it at runtime.
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"kernel.nmi_watchdog" = 0;
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};
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# Server has no audio consumers. Power-gate the HDA codec at module load
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# rather than waiting for powertop auto-tune to do it after boot.
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boot.extraModprobeConfig = ''
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options snd_hda_intel power_save=1 power_save_controller=Y
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'';
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# Apply sysfs power knobs that powertop --auto-tune cannot reach (hardened
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# kernel blocks debugfs mount, so powertop silently skips ASPM policy and
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# may only lower EPP to balance_power instead of power).
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#
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# AMD pstate EPP "power": deepest P-states, fastest core parking. Safe because:
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# - xmrig runs at Nice=19 / CPUSchedulingPolicy=idle and tolerates latency
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# - web services (caddy, jellyfin) are I/O-bound; the ~50 us extra C-state
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# exit latency is invisible behind network RTT
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# - Minecraft server benefits from single-thread boost, which pstate still
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# provides on demand even in "power" mode (just with slightly slower ramp)
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#
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# ASPM powersupersave: deepest PCIe link power states (L1.1/L1.2). The
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# pcie_aspm=force boot param enables ASPM, but the runtime policy defaults
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# to "default" which only uses L0s. powersupersave adds L1 substates for
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# all downstream devices (NVMe, AHCI, NIC).
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systemd.services.power-tune = {
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description = "Apply power-saving sysfs knobs (EPP, ASPM policy)";
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after = [ "multi-user.target" ];
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wantedBy = [ "multi-user.target" ];
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serviceConfig = {
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Type = "oneshot";
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RemainAfterExit = true;
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ExecStart = lib.getExe (
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pkgs.writeShellApplication {
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name = "power-tune";
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text = ''
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# AMD pstate energy performance preference
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for epp in /sys/devices/system/cpu/cpu*/cpufreq/energy_performance_preference; do
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[ -f "$epp" ] && echo power > "$epp"
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done
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# PCIe ASPM policy
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aspm=/sys/module/pcie_aspm/parameters/policy
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[ -f "$aspm" ] && echo powersupersave > "$aspm"
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'';
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}
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);
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};
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};
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}
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