"Syncing cpus" on a multi-cpu, dual core system

[M. L. Dodson]

On a computational chemistry list I subscribe to there is a
current thread about multi-cpu systems needing to have the cpu
frequencies synced (this is in a Linux context).  This is
evidently not just having the cpus running at nominally the same
frequency but something else in addition.  A posting in the thread
said variations less than 0.1% were not problematic.  However, the
poster said it was an issue in a dual cpu, dual core system he had
set up.

My questions are:
1. Is this real or an urban legend?
2. If real, is this a Linuxism or is FreeBSD affected as well?
3. How do you "sync" the cpus, if it is needed?
4. anything else some one wants to expound on along this line.

Bud Dodson
-- 
M. L. Dodson
Email:	mldodson-at-houston-dot-rr-dot-com
Phone:	eight_three_two-56_three-386_one