How to Disable Certain CPU Cores in Linux Scheduler Without Rebooting

Disabling Certain CPU Cores in the Linux Scheduler Without Rebooting

In some scenarios, you may want to disable certain CPU cores in the Linux scheduler without rebooting the system. This can be useful when you need to perform maintenance on a running system or when dealing with hardware issues. While the most common method to isolate CPU cores involves rebooting and using the isolcpus kernel parameter, there is a way to achieve this at runtime, without rebooting.

Understanding the Linux Scheduler

The Linux scheduler, also known as the CPU scheduler, is responsible for distributing tasks (processes and threads) among available CPU cores. The goal is to balance the load and maximize system performance. The Linux kernel provides several scheduling algorithms, such as Completely Fair Scheduler (CFS) and Deadline scheduler, to manage this distribution.

Motivation for Disabling CPU Cores

There are several reasons why you might want to disable certain CPU cores in the Linux scheduler without rebooting:

• Hardware maintenance or troubleshooting
• Temporarily disabling cores with lower performance or higher power consumption
• Balancing the load between CPU sockets in NUMA systems

Runtime Approach: Using CPU Sets

CPU sets are a Linux kernel feature that allows you to assign specific processes to specific CPU cores. By assigning all processes to a subset of CPU cores, you effectively disable the remaining cores in the Linux scheduler. This can be done at runtime without rebooting the system.

Creating a CPU Set

To create a CPU set, you need to use the /proc filesystem. First, create a new CPU set with a unique identifier:

Replace cpu_set_id with a unique identifier for your CPU set, such as a positive integer.

Adding CPUs to the CPU Set

Next, add the CPU cores you want to include in the CPU set. For example, to include CPU cores 0 and 1:

Assigning Processes to the CPU Set

Now, assign processes to the CPU set using the taskset command:

Replace pid with the process ID you want to assign and cpu_set_id with the identifier of your CPU set.

Disabling the Remaining CPUs

Finally, to disable the remaining CPU cores, create a new CPU set with all CPU cores and assign no processes to it:

While the most common method for isolating CPU cores in the Linux scheduler involves rebooting and using the isolcpus kernel parameter, it is possible to disable certain CPU cores at runtime using CPU sets. By assigning all processes to a subset of CPU cores, you effectively disable the remaining cores in the Linux scheduler.

References

• Linux kernel documentation on CPU sets: https://www.kernel.org/doc/Documentation/cpu-hotplug.txt
• taskset man page: https://man7.org/linux/man-pages/man1/taskset.1.html