Clock on compute nodes

[Predrag Punosevac]

Emre Yolcu <eyolcu at cs.cmu.edu> wrote:

> Hi Predrag,
> 
> This is a very minor annoyance, so feel free to ignore if you're busy.
> Somebody brought up before that time was set incorrectly on some compute
> nodes. For instance, it seems gpu9 is 3 minutes ahead of Pittsburgh time,
> and gpu8 is 9 minutes ahead. When you have time could you check whether the
> sync is working correctly?

Fixed! Thank you so much for the report. Clock drifting is not a minor
issue and it is very serious security problem and the best indication of
failing hardware. Unfortunately CMU School of Computer Science is
blocking NTP protocol so I run two internal NTP servers which
synchronize time via HTTP protocol as well some other tricks. In this
particular instance the culprit(s) were dead chronicd clients on GPU8
and GPU9 machines. I fixed them now.

It is also interesting to remind everyone how General Theory if
relativity affects our computing infrastructure. The biggest scientific
leap General Relativity Theory made was abandoning the concept of
absolute time. Absolute space concept was abandoned already in special
theory of relativity. The concept of absolute space-time was introduced
by Isaac Newton in order to preserve Galilean principle of relativity
which was supposed to be 4th Newton's law (originally he wanted to have
6 before reducing to three). One may refer to Arnold's Mathematical
Methods of Classical Mechanics to learn about those delicate points.
Most graduate text in physics a mute about those points which makes them
irrelevant. 

Only Poincare was able to demonstrate invariance of law's of nature
without Galilean principle of relativity thereby giving a major
push to Theory of Relativity. 

Long story short time depends on the inertial frame which means that no
two computers have the same time. Clock synchronization is essentially
averaging in order to enable us to work on the network.

Cheers,
Predrag


> 
> Best,
> 
> Emre