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Understanding Intel's RAPL Driver On Linux

Intel

Published on 06 June 2014 03:44 PM EDT
Written by Michael Larabel in Intel
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For many months now Intel has been working on RAPL support within the Linux kernel as part of their power-capping framework as a power feature for Intel hardware on Linux.

RAPL is short for Running Average Power Limit and since Sandy Bridge there has been this RAPL interface for exposing power meters and power limits. This power information is exposed through MSRs and the PCI Express config space, which in turn are exposed under Linux using this RAPL kernel code.

RAPL exposes energy counters and performance counters that Intel believes matches actual power measurements. RAPL also allows for setting power limits on the processor and DRAM. RAPL also exposes performance feedback including the time the RAPL mechanism forced the P-State below the OS-requested P-State and other metrics. Among the software taking advantage of RAPL on Linux is TurboStat, PowerTOP, and the Linux thermal daemon.

Understanding Intel's RAPL Driver On Linux

For those interested in learning more about Intel's Running Average Power Limit functionality of their modern CPUs when running an updated stack, you can read more about RAPL on Intel's 01.org.

About The Author
Michael Larabel is the principal author of Phoronix.com and founded the web-site in 2004 with a focus on enriching the Linux hardware experience and being the largest web-site devoted to Linux hardware reviews, particularly for products relevant to Linux gamers and enthusiasts but also commonly reviewing servers/workstations and embedded Linux devices. Michael has written more than 10,000 articles covering the state of Linux hardware support, Linux performance, graphics hardware drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and OpenBenchmarking.org automated testing software. He can be followed via and or contacted via .
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