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

[M. L. Dodson]

On Saturday 16 December 2006 12:30, M. Warner Losh wrote:
> In message: <200612141437.28724.mldodson at houston.rr.com>
>
>             "M. L. Dodson" <mldodson at houston.rr.com> writes:
> : 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.
>
> Linux keeps the cpu's frequencies 'synchronized' so that it can use
> the fast time keeping hardware (TSC).  FreeBSD uses different
> mechanisms for its timekeeping, so doesn't need to keep them in sync
> at all, and doesn't even try at this point.  Maybe this is what they
> are talking about...
>
> Warner

That is very much in line with the context of the postings on the
computational chemistry list I mentioned.  This is the likely
source of the issue for people on that list (very few use *BSD).
They just assume if you are not using Solaris or Irix, then you
must be using Linux of some flavor.

And this means I don't have to bother with that particular piece
of nonsense.

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