The Evolution of MKL Thread Numbers in WSL

Introduction

The world of high-performance computing is a complex and rapidly evolving landscape. One aspect that has undergone significant changes in recent times is the setting of MKL thread numbers. For those unfamiliar with this concept, let’s take a step back to understand what MKL (Math Kernel Library) is and why its thread settings are important.

What is MKL?

The Math Kernel Library (MKL) is a library developed by Intel that provides a set of optimized linear algebra functions for scientific and engineering applications. It is widely used in various fields, including data analysis, machine learning, and numerical simulations. The MKL library is particularly useful when dealing with large-scale matrix operations, which are common in many computational scenarios.

The Role of MKL Thread Numbers

The number of threads used by the MKL library can significantly impact performance, especially when working with parallelizable tasks like linear algebra operations. The MKL library uses a concept called “thread-level parallelism” to divide the workload among multiple processor cores. By adjusting the number of threads, users can fine-tune their system’s performance.

The Effectiveness of Setting MKL Thread Numbers in /etc/environment

In the past, setting the MKL thread numbers in /etc/environment was an effective way to control the number of threads used by the MKL library. This file allows administrators to define environment variables that apply to all processes running on the system. By modifying this file, users could adjust the number of threads used by the MKL library and observe a corresponding impact on performance.

The Issue with WSL

However, in recent times, setting MKL thread numbers in /etc/environment has lost its effectiveness. Despite restarting the system and updating the environment variables, the changes do not seem to have any noticeable effect on the number of threads used by the MKL library.

Understanding the Context: From VMs to WSL

One possible reason for this change is the shift from using virtual machines (VMs) to Windows Subsystem for Linux (WSL). When using a VM, setting environment variables in /etc/environment would indeed have an effect on the number of threads used by the MKL library. This was because the VM’s underlying operating system was not aware of the changes made to the environment variables.

However, when using WSL, the situation is different. WSL is a layer on top of a native Windows environment, which means that it inherits many of the characteristics of the underlying Windows OS. One such characteristic is the behavior of environment variables in /etc/environment.

The Reality of Editing /etc/environment in WSL

Editing ~/.profile and adding the necessary environment variables or commands to set the MKL thread numbers has become a viable alternative for users running WSL.

Why Does Editing /etc/environment Not Work in WSL?

There are several reasons why editing /etc/environment does not work in WSL:

• WSL’s Isolation Layer: WSL provides an isolation layer that separates it from the underlying Windows OS. This means that changes made to environment variables or other system settings in ~/.profile or other configuration files take precedence over equivalent changes made in /etc/environment.
• Environment Variable Scope: Environment variables defined in /etc/environment apply globally, whereas those defined in ~/.profile have a local scope. When running WSL, the environment variables set in ~/.profile override those defined in /etc/environment, making it unnecessary to rely on the latter.
• WSL’s Customization Options: One of the benefits of using WSL is its ability to customize its behavior to suit user needs. By modifying configuration files like ~/.profile, users can control various aspects of their WSL experience, including environment variables.

The Alternative: Exporting MKL_NUM_THREADS

For those who need finer-grained control over their MKL thread numbers, exporting MKL_NUM_THREADS as an environment variable in ~/.profile offers a more flexible solution. This approach allows users to adjust the number of threads used by the MKL library on a per-session basis.

# ~/.profile (example)
export MKL_NUM_THREADS=16

This code sets the value of MKL_NUM_THREADS to 16, which can be adjusted as needed.

Conclusion

The world of high-performance computing is constantly evolving. As new technologies and frameworks emerge, it’s essential to stay informed about changes that may impact our work. In this case, the shift from using virtual machines to Windows Subsystem for Linux has introduced a new variable in how we set MKL thread numbers. By understanding these changes and adapting our strategies accordingly, we can continue to optimize our performance and make the most of our computing resources.

Additional Considerations

There are several other factors that may influence the effectiveness of setting MKL thread numbers:

• System Configuration: The specific configuration of your system, including its processor architecture, number of cores, and available memory, can significantly impact performance.
• Library Optimizations: Some libraries, like BLAS (Basic Linear Algebra Subprograms) or LAPACK (Linear Algebra Package), may be optimized for specific thread counts. Understanding these optimizations can help you make informed decisions about your thread settings.
• Parallel Computing Frameworks: When working with parallel computing frameworks like OpenBLAS or Intel’s MKL-DNN, the choice of thread count and library configuration can have a significant impact on performance.

By considering these factors and adapting our approach to accommodate changing environments, we can continue to achieve optimal performance in our high-performance computing endeavors.

Last modified on 2025-01-17