Measuring scheduling latencies
All the configuration and tuning you may do will be pointless if you cannot show that your device meets the deadlines. You will need your own benchmarks for the final testing but I will describe here two important measurement tools: cyclictest and Ftrace.
cyclictest
cyclictest was originally written by Thomas Gleixner and is now available on most platforms in a package named rt-tests. If you are using the Yocto Project, you can create a target image that includes rt-tests by building the real-time image recipe like this:
$ bitbake core-image-rt
If you are using Buildroot, you need to add the package, BR2_PACKAGE_RT_TESTS in the menu Target packages | Debugging, profiling and benchmark | rt-tests.
cyclictest measures scheduling latencies by comparing the actual time taken for a sleep to the requested time. If there was no latency they would be the same and the reported latency would be zero. cyclictest assumes a timer resolution of less than one microsecond.
It...
