Variorum Overview

Variorum is a production-grade software infrastructure for exposing low-level control and monitoring of a system’s underlying hardware features, with a focus on power, energy and thermal dials. It is a significant evolution based on an older open-source library developed at LLNL, called libmsr. Variorum is vendor-neutral, and can easily be ported to different hardware devices, as well as different generations within a particular device. More specifically, Variorum’s flexible design supports a set of features that may exist on one generation of hardware, but not on another.

Design Principles

To guide the development of Variorum, we focused on a set of important requirements extracted from our learnings with the development of libmsr. Here are Variorum’s requirements:

• Create device-agnostic APIs: We do not want to require the user to have to know or understand how to interface with each device. The library is built for a target architecture, which may be heterogeneous, and can collect data from each device through a single front-facing interface.

• Provide a simple interface: We want users and tool developers to not only collect information from the underlying hardware, but also to have the ability to control various features.

• Ease in extending to new devices and generations within a device: Variorum makes it easy to support new features, deprecate old features among generations of devices, and adapt features that may have different domains of control from one generation to another (i.e., sockets, cores, threads).

System Diagram