Daniel Franke <dfoxfra...@gmail.com>:
> Scheduler timeslices haven't changed much. The current default on
> Linux is 1ms and it's been that way for a long time. What's changed is
> that everybody has multicore processors now, so contention almost
> never happens.
Your historical baseline isn't long enough. The NTP code has roots in
the 1980s, but there was a massive change in Unix schedular
granularity in the 1990s as typical clock speeds went from 10e7Hz to
10e8Hz. On Linux it happened early enough that the changeover was
poorly documented and is now largely forgotten; it's reasonable
that you don't know about it.
I actually learned this the hard way when it happened; one of my older
small projects was a real-time game (Tetris implemented for curses) with a
delay loop that became unplayably fast after the jump. If I groveled
through my git logs I could probably pin down when I had to change it.
The NTP packet-stamp code dates from the before time, when sampling lag
due to timeslice granularity was an order of magnitude or more worse
than it is now. From some of its details I'd guess it was written about
'87 or '88.
--
<a href="http://www.catb.org/~esr/";>Eric S. Raymond</a>
My work is funded by the Internet Civil Engineering Institute: https://icei.org
Please visit their site and donate: the civilization you save might be your own.
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