How does changing the scheduler/nice value compare to applying the PREEMPT_RT patch to the Linux kernel?

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Changing the scheduler/nice value and applying the PREEMPT_RT patch to the Linux kernel are two different approaches to achieve real-time performance in a Linux system.

Changing the scheduler/nice value can affect the priority level of processes, but it may not provide deterministic behavior for real-time applications. It may also not guarantee that a process will get all the CPU resources it needs for its desired performance.

On the other hand, applying the PREEMPT_RT patch to the Linux kernel provides hard real-time performance by ensuring that all processes can be preempted at any time, even if they are in a critical section. This means that real-time processes can get immediate access to CPU resources without delay, which is essential for applications such as control systems, robotics, and video/audio streaming.

In summary, changing the scheduler/nice value can improve performance for non-critical applications, while applying the PREEMPT_RT patch is necessary for hard real-time applications that require deterministic behavior and immediate access to CPU resources.