c - Different scheduling jitter for task frequencies -


recently implemented qnx neutrino rtos on zynq-7000 platform (arm a9) , measured scheduling jitter different task frequencies no cpu load. in test wait in msgreceive function pulse generated timer. read high frequency clock fpga (100mhz). measured scheduling jitter 10hz, 100hz, 1khz, 10khz , 100khz tasks , got strange results. short period task got (-300,+300) nanoseconds jitter, longer periods got following:

  • 1khz task had (+600, +1300) nanoseconds jitter
  • 100hz task had (+8, +12) microseconds(!) jitter
  • 10hz task had (+69,+71) microseconds jitter

jitter not grow bigger longer period tasks, greater zero. didnt expect such differencies. provide explanation of such behaviour? might explained posix standard, allows timers expire not prematurely overhead? why did become more visible long period tasks?


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