"slewing" the system clock

[wales at UCLA-LOCUS.ARPA]

From:            Rich Wales <wales at UCLA-LOCUS.ARPA>

Here's an idea (not a new one, I don't think):

How about a way to reset a UNIX system's idea of the time of day by
"slewing" the clock (i.e., speeding up or slowing down until the system
clock is correct)?

I think this could be done on the VAX, for example, by loading the NICR
(Next Interval Count Register) with a nonstandard value, then restoring
the original value later on.

Doing this would seem to be less traumatic to running processes than
simply changing the clock in one big quantum leap.  Particularly so if
the clock needs to be reset backwards (which, in addition to its effect
on running processes, could also mess up incremental dumps).

I would still want to keep the current "stime" system call interface
intact, for use when the time is "way off" and needs to be set correctly
"right now".

Has anyone out there done this, or seriously considered doing it?  Are
there any other operating systems which do this kind of thing?

-- Rich