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I am currently running Debian 9 stretch with a PREEMPT RT kernel patch on a beaglebone black. My kernel version is:

4.4.155-ti-rt-r155

I have performed a latency test by writing a kernel module that turn an LED on after an interrupt is triggered by a button push. The measured latency between the button push and the LED turning on is 330 microseconds. This is a bit strange since I expected a real time kernel to have a low latency (about 10-30 microseconds). Is there an extra step that I need to do to, perhaps in code, to get low latency?
Thank you.

programmer25
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    an RT kernel does not magically make everything fast. https://rt.wiki.kernel.org/index.php/Frequently_Asked_Questions#What_sort_of_real-time_performance_should_I_expect.3F and how to write user space apps for RT https://rt.wiki.kernel.org/index.php/HOWTO:_Build_an_RT-application – TBR Aug 30 '20 at 08:04

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