rtmon

rtmon [options]

-f
    Directs the output of rtmon to the specified filename instead of standard output.

-d
    Sets the delay interval, in seconds, between consecutive reports or updates from rtmon.

-s
    Enables the display of detailed scheduling-related information and statistics.

-m
    Activates the monitoring and reporting of memory-related statistics.

-l
    Focuses the output on latency-specific data, such as minimum, maximum, and average latencies.

-t
    Shows information and statistics related to active tasks and processes.

-c
    Specifies a particular CPU core (e.g., 0, 1) to monitor exclusively.

-v
    Increases the verbosity of the output, providing more detailed information.

-h
    Displays a brief help message with available command options and exits.

-r
    Resets the collected statistics, allowing for a fresh measurement period.

The rtmon command is a specialized utility designed for monitoring the real-time performance characteristics of a Linux system, particularly those running with real-time kernel patches like PREEMPT_RT. It provides insights into various kernel activities crucial for deterministic execution, such as scheduler behavior, interrupt latencies, and context switches.

Developers and system engineers utilize rtmon to diagnose and debug real-time applications, identify sources of non-determinism, and ensure systems meet strict timing requirements. It helps in understanding if tasks are being scheduled predictably, if interrupts are processed promptly, and if there are unexpected delays impacting critical operations. The tool collects and displays statistics that highlight potential issues, making it invaluable for optimizing real-time embedded systems, industrial control, audio/video processing, and other latency-sensitive applications.

rtmon is primarily effective on Linux systems running a real-time kernel (e.g., PREEMPT_RT), as it leverages real-time specific kernel features.
Execution often requires elevated privileges (e.g., root) to access necessary kernel interfaces and tracepoints.
It's typically part of the rt-tests suite and may not be pre-installed on standard Linux distributions.
Interpreting its output requires a basic understanding of real-time operating system concepts and kernel internals.

When run, rtmon typically presents statistics including minimum, maximum, and average latencies for various kernel events (like scheduling delays or interrupt response times). It may also show counts of context switches, interrupt requests (IRQs) per CPU, and details about process priority and CPU utilization, all critical for assessing real-time performance. The exact output format can vary slightly depending on the invoked options and the specific version of the tool.

rtmon is a cornerstone tool in the real-time Linux development workflow. It helps in validating the effectiveness of real-time configurations, debugging issues like priority inversions or excessive jitter, and profiling custom real-time applications to ensure they meet stringent timing deadlines. It is often used in conjunction with other rt-tests tools like cyclictest for comprehensive real-time system analysis.

rtmon originated as a component of the rt-tests suite, a collection of utilities developed to benchmark and validate the real-time capabilities of the Linux kernel, specifically in conjunction with the PREEMPT_RT patchset. Its development has closely paralleled the evolution of real-time Linux, serving as a vital tool for developers and engineers working on low-latency and deterministic systems. It has been instrumental in identifying performance bottlenecks, verifying real-time integrity, and ensuring predictable behavior in demanding applications like embedded systems, robotics, and industrial control.

cyclictest(1), perf(1), ftrace(1), top(1), stress-ng(1)