You are here: Appendices > Appendix L Cray-Specific Power Management and Energy-Consumption-by-Job Accounting > Cray Power Management Overview

L.1 Cray Power Management Overview

The Cray XC30 and XC40 systems can perform power management using various schemes supported by the Moab Workload Manager, which includes power management of actively running compute nodes as well as management of power states for idle compute nodes.

L.1.1 Cray XC Systems Power Management

For the management of the energy consumption of actively running compute nodes, Cray XC systems provide processor P-state and Linux power governor policy management support. For the management of the energy consumption of idle compute nodes, Cray XC systems provide S-state support.

Actively Running Node Power Management

The Cray ALPS system provides processor P-state and Linux power governor policy management at the time of job start; that is, a user can submit a job and request the job's compute nodes operate at a specific clock frequency (P-state) or with a specific Linux power governor policy for the duration of the job. The Cray ALPS subsystem sets the requested frequency or power governor policy when it sets up the job's node allocation reservation. ALPS cannot change the requested frequency or power governor policy while the job executes. After the job finishes, the nodes' frequency or power governor policy are restored to the setting before ALPS set up the node reservation.

Idle Node Power Management

The new Cray Advanced Power Monitoring and Control (CAPMC) system provides a means for the Moab Workload Manager to manage the power state of individual compute nodes. Specifically, the CAPMC system can power up (S0 state) or shut down (S5 state) compute nodes.

At the time of the Cray XC30 system introduction, only a system administrator using the System Management Workstation (SMW) could perform all Cray XC power management functions. Since that time, Cray has provided a new command line utility named "capmc" that allows administrators and/or workload managers to manage the power state of compute nodes from "login" nodes.

L.1.1.A Moab Power Management on Cray XC Systems

Moab has two methods of performing power management; Moab-only and Moab+Moab Web Services (Moab+MWS). The two methods are described in the Green Computing Overview of the Moab Administrator's Guide Version 9.0.1.

9.0.1 uses the Moab-only method of power management for Cray XC systems, which requires four Cray-specific power management scripts Cray ported from Moab's OpenIPMI-based "reference" scripts to the XC.