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Re:One second per second is harder than it sounds by easytiger on Tuesday July 22, 2014 @03:50AM (#8067782)
This is a terrible idea when dealing with an application other than "users checking the time on their system clock".

Performing hard resets of the clock continually is a catastrophic infrastructure failure. A high performance 24/7 application that relies on sub millisecond let alone sub microsecond accuracy across multiple physical systems will be utterly destroyed by this approach.

Re:One second per second is harder than it sounds by jacquesm on Tuesday July 22, 2014 @09:33AM (#8068856)
Not just that, monotonicity could be impaired.
Re:One second per second is harder than it sounds by wlesieutre on Tuesday July 22, 2014 @10:08AM (#8069034)
To elaborate, monotonicity means that a value is either always increasing or always decreasing, and never changes direction. If a program is built on the assumption that time always goes forward, it may not like you setting the clock back 0.000000001sec every hour.
Re:One second per second is harder than it sounds by shadowfox on Tuesday July 22, 2014 @03:42PM (#8071162)
Many license management software are especially bothered by time changes of this sort.
Re:One second per second is harder than it sounds by wlesieutre on Tuesday July 22, 2014 @04:35PM (#8071429)
Very true, a lot of software with time limited trials or features like "check out a network license for 30 days of offline use" used to be easy to bypass by turning your clock back so that it never expired.

This is pretty widely fixed now, but often overzealously. Clock changed unexpectedly? User is a dirty pirate and the license should deactivate.

Re:One second per second is harder than it sounds by lamontcg on Tuesday July 22, 2014 @09:21PM (#8072442)
Reading comprehension...

I had 30,000 servers, all but 6 of them were not getting hard resets. 6 of them were getting hard resets every hour because they were sick.

Occasionally a ntpd on a server would go a little crazy and it would get a few hard resets. This script got it back into spec so that it didn't need hard resets.

I mentioned specifically that you can't send hard resets to ntpd more than about once an hour or it won't have time to settle and you'll wind up in a situation where you are constantly sending hard resets to it (which is bad).

I took out the nightly forced hard resets of ntpd specifically because it affected monotonic time.

If you look at the algorithm I wound up with ntpd will only be reset if:

a. it is already crashed and not running

b. it is self-reporting that it is out of synch

c. is is more than 50ms out of synch with an upstream time server

In all of those cases, you have already lost the battle to get sub-microsecond accuracy.

Re:One second per second is harder than it sounds by pjc50 on Tuesday July 22, 2014 @04:48AM (#8067908)
If the clock is drifting substantially then your high-precision application will already be in serious trouble.
Re:One second per second is harder than it sounds by easytiger on Tuesday July 22, 2014 @05:32AM (#8068030)
If your clock solution, GPS + Sync, is drifting then your infrastructure is broken and your platform is not fit for service.