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Date: Mon, 02 Jan 2012 06:42:32 +0100
From: Marco Steinbach <coco@executive-computing.de>
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To: Dennis Glatting <freebsd@pki2.com>
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Cc: freebsd-questions@freebsd.org
Subject: Re: CPU MHz discrepency
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Dennis Glatting wrote on 31.12.2011 16:52:
> Curios here. 
> 
> My BIOS reports my CPU at 4,023 MHz but when FreeBSD boots it says
> "3973.35-MHz." How is this determined? Seems like an off-by-one error
> somewhere.
> 
> MB: ASUS Crosshair V FORMULA, latest BIOS, overclocked.
> 
> dmesg output:
> 
> Tasha> dmesg
> Copyright (c) 1992-2011 The FreeBSD Project.
> Copyright (c) 1979, 1980, 1983, 1986, 1988, 1989, 1991, 1992, 1993, 1994
>         The Regents of the University of California. All rights
> reserved.
> FreeBSD is a registered trademark of The FreeBSD Foundation.
> FreeBSD 8.2-STABLE #7: Fri Dec 30 18:15:12 PST 2011
>     root@Tasha:/disk-1/src/sys/amd64/compile/TASHA amd64
> Timecounter "i8254" frequency 1193182 Hz quality 0
> CPU: AMD FX(tm)-8150 Eight-Core Processor            (3973.35-MHz
> K8-class CPU)
>   Origin = "AuthenticAMD"  Id = 0x600f12  Family = 15  Model = 1
> Stepping = 2

In your case you might want to take a look at the printcpuinfo function 
in ${SRC_BASE}/sys/md64/amd64/identcpu.c for starters.  Especially the 
CPUCLASS_K8 case in the second switch statement.

MfG CoCo