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Libmsr is no longer actively maintained -- libmsr has evolved into Variorum, which can be found on github:


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Welcome to Libmsr, a friendly (well, friendlier) interface to many of the model-specific registers in Intel processors. Now with PCI configuration register support for some Intel hardware.

version 0.3.1


Libmsr is no longer being actively developed. Variorum is an evolution of and a successor to libmsr. Variorum can be found on github:

Last Update

24 March 2020



Libmsr provides an interface to accessing the model-specific registers (MSRs) on Intel platforms, which provide privileged functionality for monitoring and controlling various CPU features.


Installation is simple. You will need CMAKE version 2.8 or higher and GCC. In most cases, the installation is as follows:

$ cmake . -DCMAKE_INSTALL_PREFIX=${HOME}/build/libmsr
$ make
$ make install

The installation depends on a master.h file, which defines the offsets for several MSRs given a particular architecture (e.g., Sandy Bridge, Ivy Bridge, Haswell, etc.). The auto-configuration tool can be forced to use the header file of a specific architecture or can auto-detect the architecture. To specify a particular architecture, run cmake with the option -DLIBMSR_TARGET_ARCH=<ARG> where ARG is in hexadecimal. In the future, we plan to have a set of architecture-specific configuration files that can be pre-loaded to CMake to populate the cache.

Currently supported architectures are Intel Xeon v1-3 (Sandy Bridge, Ivy Bridge, and Haswell server processors). The library technically supports all processors based on these architectures, but some features may be missing from client products. Using the wrong header file is likely to cause problems.

Supported Architectures:

2D (Sandy Bridge)       57 (Knights Landing)
3E (Ivy Bridge)
3F (Haswell)
4F (Broadwell)
55 (Skylake)*

If you are unsure of your architecture number, check the "model" field in lscpu or /proc/cpuinfo (note that it will not be in hexadecimal).

*The Skylake support is currently experimental and requires more testing/validation.


This software depends on the files /dev/cpu/*/msr being present. Recent kernels require additional capabilities. We have found it easier to use our own MSR-SAFE kernel module with R/W permissions, but running as root (or going through the bother of adding the capabilities to the binaries) is another option.

If you need PCI configuration register (CSR) support in Libmsr, you MUST have CSR-SAFE installed. This code is not currently on Github -- you will need to request it.

Call msr_init() before using any of the APIs.

For sample code, see libmsr_test.c in the test/ directory.

Our most up-to-date documentation for Libmsr can be generated with make doc and make latex_doc for HTML and PDF versions, respectively. There are also some useful PDF files in the documentation/ directory.


Barry Rountree, Project Lead,
Stephanie Brink, Developer,

Please feel free to contact the developers with any questions or feedback.

We are collecting names of those who have previously contributed to libmsr over the years. See the current list in the AUTHORS file. Please contact the developers to have your name added to the list.


libmsr is released under the GPLv2.1 license. For more details, see the LICENSE file.