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Power limits and budgets

A power limit changes what a card draws. A power budget changes where work goes. They are different mechanisms with different requirements, and conflating them is the mistake this page exists to prevent.

Two different things#

Reading what a card allows#

nodeau power
nodeau power --json

Every card has a power limit it enforces and a range it will accept. Nodeau reads both and reports them, and changes nothing unless you ask.

Setting a limit#

nodeau power set --device GPU-c080d9be-9a09-0895-7162-fdb28011a7fd --limit 250
nodeau power set --device GPU-c080d9be-… --clear

Rules Nodeau holds itself to:

• The card is named by UUID, never by an index, because an index moves.
• The requested watts must lie inside **that device's own currently reported range**, read from the device at the moment of the write.
• The current and default limits are recorded before any change.
• A failed application is never reported as applied.
• The desired state is declarative and reconciled, because a power limit survives no reboot, no driver reload and no device reset.

This is local: it applies to a card in the machine you run it on and never crosses the network. There is no way to set a power limit remotely, and the capability to do so is not built.

What it will never write#

No firmware. No VBIOS. No voltage. No clocks. No unsupported sysfs. Nodeau uses NVIDIA's own supported power-limit interface and nothing else, and there is no "run this privileged GPU command" surface, local or remote.

If the card does not support it#

A card whose reported range does not admit the value you asked for refuses, and says what the range is. A card that does not support software power limits at all is reported as such rather than silently unchanged.

The scheduling power budget#

nodeau scheduling constraints --node nodeforge --power-budget 400
nodeau scheduling constraints --node nodeforge --idle-watts 60
nodeau scheduling constraints --node nodeforge --clear

An operator ceiling on predicted power that makes a candidate infeasible. It needs no privilege, writes nothing to any device, and works on hardware where power-limit mutation is unsupported.

--idle-watts tells Nodeau what a machine draws with nothing running, so waking it is counted as a cost rather than as free.

Constraints are hard: Nodeau refuses to place work rather than exceed one, and no scheduling mode can score around them.

Power and scheduling modes#

The scheduling mode decides how much weight predicted power carries when choosing between candidates:

nodeau placement explain <name> prints the predicted power of the placement it chose and of the ones it did not.

Documentation for the current published build, the beta channel. Something here wrong or missing? Tell us — a report from a machine we have never seen is the most useful thing we get.