CPUISSET

CPUISSET is a command-line utility available in Unix-like operating systems, primarily used to determine the set of available CPU cores on a system. It is part of the Linux kernel's debugging tools and is commonly found in distributions that include the kernel source code or debugging packages. The tool is particularly useful for applications requiring fine-grained control over CPU affinity, such as high-performance computing, parallel processing, or system monitoring tasks.

The command operates by reading the contents of the `/sys/devices/system/cpu/online` file, which lists the CPU cores currently available to the system. CPUISSET provides a more user-friendly and structured way to interpret this information compared to directly parsing the file. It outputs a bitmask or a list of CPU indices, allowing users to identify which cores are active and available for scheduling processes.

One of the primary use cases for CPUISSET is in conjunction with other utilities like `taskset` or `numactl`, which allow administrators to bind processes to specific CPU cores or NUMA (Non-Uniform Memory Access) nodes. By understanding the available CPU set, users can optimize performance by ensuring critical processes run on dedicated cores, reducing latency, and improving throughput in multi-core environments.

CPUISSET is particularly relevant in server environments, where workload distribution across multiple cores is essential for handling high-demand applications. It is also useful for troubleshooting CPU-related issues, such as identifying inactive or offline cores that may affect system performance. The tool is lightweight and does not require additional dependencies beyond those provided by the Linux kernel.

While CPUISSET is not a standalone application in most distributions, it is often included in kernel debugging packages or can be compiled from the kernel source code. Its simplicity and direct interaction with the kernel make it a valuable tool for system administrators and developers working with CPU-intensive workloads.