yes, some idea about that
in fact the time I ve given is the total overhead time needed by the scheduler to
1- verify if the task should be interupted. this includes verifying time spent in the task and comparing it to a "quantum". this garantees that all the task will get a certain amount of cpu time (unless they slep of course)
2-calculate overage time spent in this task over the 2/4/8/16 last cycles
3- check which task is next
4- switch task context to next
5- calculate overage time spent since we enter in this task (2/4/8/16 last cycles), to update the overall cycle time variable.
and then it is very ok compared to the pure assembly context switch routine which is very fast as you pointed out.
the steps 2 & 5 can now be de activated in a new version of the library (pre processing) and this will probably divide the time given by 2, but I need a oscilloscope to check this !
last but not least, the library isnt using any interrupt but systematic calls to the Arduino Millis() and this approach is very flexible but consume more cpu than traditional RTOS systick method, especially on Arduino compared to Teensy which is better optimized.
here we are