How do you know you have tested all required permutations of interference channels?

While it may not be necessary to test all permutations of interference channels, as some permutations may never be able to produce a worst-case timing result, a strong justification is required to remove the need to test a permutation. As such, the initial starting point may be to test all permutations of interference channels and the software under test, mapped to all active cores. Where you can justify why specific permutation(s) could never produce a worst-case timing result, for example where interference channels are mutually exclusive, you can remove these permutations from your analysis. Information helpful to this can be found in the MACH¹⁷⁸ Foundations white paper WCET Considerations.