7.2.3 Applying the Real-Time Kernel

The RDKS100 enables the real-time kernel by default. A real-time kernel is an operating system kernel capable of providing more precise and reliable response times, commonly used in applications with high time-sensitivity requirements, such as robotic control and industrial automation. Below are commands for enabling and disabling the real-time kernel, along with common use cases and testing methods.

Real-Time Performance Testing

When testing the performance of a real-time kernel, a commonly used tool is rt-tests, which includes multiple test programs for evaluating real-time kernel performance. The following is an example of using rt-tests for performance testing:

Installing the rt-tests Tool

If rt-tests is not yet installed, use the following commands to install it:

sudo apt update
sudo apt install rt-tests

Running the cyclictest

cyclictest is a commonly used test within rt-tests for evaluating a system's timing behavior and response latency. Execute the following command to run the cyclictest:

sudo cyclictest -l50000000 -m -S -p90 -i200 -h400

This command runs a real-time performance test with the following parameters:

• -l50000000: Sets the number of test iterations.
• -m: Instructs cyclictest to lock current and subsequent memory pages using mlock during the test, preventing swapping from affecting results.
• -S: Specifies a standard SMP architecture test where all threads use the same -a, -t, -n, and priority settings.
• -p90: Specifies the real-time thread priority. -p90 means the test runs under real-time scheduling class with priority 90.
• -i200: Sets the sleep interval (in microseconds) for test threads.
• -h400: After completion, outputs a histogram showing the count of latencies below the specified threshold (400 microseconds).

The test results will display the system’s minimum, maximum, and average latency, along with other performance statistics.

Analyzing Test Results

Analyze the cyclictest results to evaluate the real-time kernel's performance. Pay close attention to the minimum and maximum latencies to ensure they fall within acceptable ranges. A lower maximum latency and more consistent latency values indicate better real-time kernel performance. The figures below show test results obtained while using the real-time kernel and running the /app/pydev_demo/03_mipi_camera_sample example.

The fields in the cyclictest output have the following meanings:

• T: Thread number and thread ID used in the test.
• P: Priority used during the test. In your output, the value is 90, indicating the test ran under real-time scheduling class with priority 90.
• I: Expected wake-up interval (in microseconds) for the latency measurement thread.
• C: Number of latency measurements taken (i.e., loop count).
• Min: Minimum latency (in microseconds) observed in the current test cycle.
• Act: Actual latency (in microseconds) observed in the current test cycle.
• Avg: Average latency (in microseconds) observed in the current test cycle.
• Max: Maximum latency (in microseconds) observed in the current test cycle.