quad buffered frame rate confusion

[michaelrepucci]

If the maximum deviation from the expected value were within 1 ms I would be happy. On my system it is not. At 120 Hz, the expected frame interval is around 8.333 ms. On one run, where the frame rate never noticeably dropped below 120 Hz, I get values in the range from 3.862 ms to 21.94 ms (see the attached histogram). Granted the variation is small; the standard deviation is 0.579 ms. (In the attached figure, counts above 20 are truncated.) However, the longer and shorter values, if accurate, suggest that frames are occasionally being dropped or skipped.