How to Use the Command 'taskset' (with examples)

The taskset command in Linux is a powerful utility for managing CPU affinity for processes. CPU affinity refers to the binding of a process to a specific central processing unit (CPU) or range of CPUs. By setting CPU affinity, you can control which CPUs a process can execute on, which can lead to performance optimizations. This is particularly useful in situations where you want processes to run on specific CPUs to improve cache performance or reduce the contention among processes.

Use Case 1: Get a Running Process’ CPU Affinity by PID

Code:

taskset --pid --cpu-list pid

Motivation:

Retrieving the CPU affinity of a currently running process can be crucial for performance monitoring and debugging. By knowing on which CPUs a process is allowed to run, system administrators and developers can understand resource utilization and potentially identify bottlenecks or issues in the system’s scheduling.

Explanation:

• taskset: The command used to manipulate or retrieve the CPU affinity of processes.
• --pid: Indicates that the command will apply to an existing process identified by its PID (process identification number).
• --cpu-list: Specifies that a list of CPUs is being used, either for querying or setting affinity.
• pid: The process ID of the running process whose CPU affinity is being queried.

Example Output:

pid 1234's current affinity list: 0-3

This output indicates that the process with PID 1234 can run on CPUs 0 through 3.

Use Case 2: Set a Running Process’ CPU Affinity by PID

Code:

taskset --pid --cpu-list 1 1234

Motivation:

Setting the CPU affinity for a running process helps in managing system performance by ensuring that a specific process uses particular CPUs. This is beneficial when managing system resources in high-load situations or running multiple processes with high CPU demand concurrently.

Explanation:

• taskset: The core command for setting CPU affinity.
• --pid: Specifies that an active process identified by a PID is being modified.
• --cpu-list: Indicates that a specific list of CPU cores will be used for setting the affinity.
• 1: Represents the CPU ID that the process will be restricted to.
• 1234: The PID of the process for which the CPU affinity is being set.

Example Output:

If successful, the command typically does not produce any output. However, checking CPU affinity again would show:

pid 1234's current affinity list: 1

This means the process is now bound to CPU 1 only.

Use Case 3: Start a New Process with Affinity for a Single CPU

Code:

taskset --cpu-list 2 command

Motivation:

Sometimes a new process may need to run on a specific CPU to prevent it from interfering with other processes or to take advantage of specific hardware attributes of that CPU. This can ensure efficient utilization of resources and can help in improving cache efficiency due to data locality.

Explanation:

• taskset: The command being used to define CPU affinity for new processes.
• --cpu-list: Indicates that a list of specific CPUs for executing the new process is provided.
• 2: Specifies that the new process should run on CPU 2.
• command: The specific command or process to be executed, bound to the defined CPU ID 2.

Example Output:

Assuming the command executed does not fail, no output is typically given by taskset. It simply enforces the CPU affinity.

Use Case 4: Start a New Process with Affinity for Multiple Non-Sequential CPUs

Code:

taskset --cpu-list 1,3,5 command

Motivation:

Running a process on non-sequential CPUs can be useful in systems where CPUs 1, 3, and 5, for example, are underutilized or if there’s a need to distribute workload evenly across available CPUs without being sequential for specific reasons, such as avoiding known hardware issues at particular CPU boundaries.

Explanation:

• taskset: Indicates initiating a process with specified CPU affinities.
• --cpu-list: Command argument for specifying a list of targeted CPUs.
• 1,3,5: These CPU IDs represent the specific CPUs the process should execute on.
• command: Represents the new command or application to run with specified CPU constraints.

Example Output:

Once the process starts with the given affinities, there’s generally no direct output, although resource monitoring tools would show the process running on the specified CPUs.

Use Case 5: Start a New Process with Affinity for CPUs 1 through 4

Code:

taskset --cpu-list 1-4 command

Motivation:

Starting a process with affinity for a range of sequential CPUs can be ideal when attempting load balancing across multiple CPUs, especially in multi-threaded applications where spreading workload consistently across adjacent CPUs can optimize performance and cache usage.

Explanation:

• taskset: The command used to enforce CPU execution parameters.
• --cpu-list: Used to identify the CPUs’ range the command will target.
• 1-4: Denotes all CPUs from 1 to 4 inclusive, suggesting a sequential reservation for process execution.
• command: The executable or task intended for setting with the specified CPU limits.

Example Output:

In usual cases, the taskset command does not provide a standard output. Successful execution implies enforced CPU restrictions as specified.

Conclusion:

The taskset command is an invaluable tool for system administrators and developers seeking to optimize computational processes and efficiently utilize system resources. By controlling CPU affinities, this command allows for fine-tuning of a process’s execution environment, potentially improving performance and resource management across diverse applications and workloads.