Tuning the system

Introduction

Optimizing your Linux installation for real-time deterministic performance involves several steps. This document provides a comprehensive guide, explaining each step and its impact on system behavior. Always exercise caution and test changes in a controlled environment before applying them to a production system.

Bash Script

The following Bash script performs real-time optimization tasks, addressing CPU affinity, stopping systemd processes, and additional tweaks.

#!/bin/bash

# Set CPU affinity for specific cores
isolated_cores="0,2,4"
echo $isolated_cores > /proc/irq/default_smp_affinity

# Move non-kernel threads to isolated cores
for pid in $(ps -e -o pid,cmd | awk '$2 != "kthreadd" && $2 != "migration" {print $1}'); do
    taskset -ac $isolated_cores $pid
done

# Additional tweaks for real-time performance
sysctl -w kernel.sched_rt_runtime_us=-1
sysctl -w kernel.sched_rt_period_us=1000000

# Disable CPU frequency scaling
for cpu in /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor; do
    echo "performance" > $cpu
done

# Lock memory to a specific core
target_pid=<your_process_pid>
mlockall -cp $target_core

Replace <your_process_pid> with the PID of the process you want to lock the memory for.

Explanation

  1. CPU Affinity: - Purpose: Isolates specific CPU cores for real-time tasks. - Effect: Reduces contention and interference from non-real-time tasks, improving determinism.

  2. Thread Affinity: - Purpose: Moves non-kernel threads to isolated cores. - Effect: Ensures that user-level threads are executed on dedicated cores, minimizing context switching.

  3. Additional Tweaks: - Purpose: Fine-tunes scheduler parameters for real-time performance. - Effect: Adjusts the scheduler’s behavior to prioritize real-time tasks.

  4. Disable CPU Frequency Scaling: - Purpose: Sets CPU frequency to maximum performance. - Effect: Prevents frequency scaling, ensuring consistent high performance for real-time tasks.

  5. Memory Locking: - Purpose: Locks critical application memory in RAM. - Effect: Prevents swapping, ensuring that critical data remains in fast, non-swappable memory.

Additional Techniques

  1. Preemption and Kernel Configurations: - Purpose: Enhances kernel responsiveness for real-time workloads. - Effect: Reduces latency by allowing the kernel to preempt lower-priority tasks.

  2. IRQ Affinity: - Purpose: Assigns IRQs to specific CPU cores. - Effect: Improves determinism by avoiding IRQ processing on non-isolated cores.

  3. Thread Priority: - Purpose: Sets real-time priority for critical threads. - Effect: Ensures that high-priority threads are scheduled with minimal delay.

  4. Memory Locking: - Purpose: Ensures critical application data is not paged out. - Effect: Prevents potential delays caused by accessing data from slower storage.

  5. RT Preempt Patches: - Purpose: Introduces real-time preemption patches to the Linux kernel. - Effect: Improves kernel responsiveness and reduces latency for real-time tasks.

Conclusion

Real-time optimizations demand careful consideration and testing. Understand the implications of each adjustment on your system and test thoroughly before applying changes to a production environment.