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Date: Mon, 25 Aug 2008 22:21:42 +0200
From: Dimitry Andric <dimitry@andric.com>
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To: Renato Botelho <rbgarga@gmail.com>
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Cc: cvs-src@freebsd.org, src-committers@freebsd.org, cvs-all@freebsd.org,
	John Baldwin <jhb@freebsd.org>
Subject: Re: cvs commit: src/sys/i386/cpufreq est.c
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On 2008-08-25 21:27, Renato Botelho wrote:
> cpu0: <ACPI CPU> on acpi0
> est0: <Enhanced SpeedStep Frequency Control> on cpu0
> est0: Guessed bus clock (high) of 200 MHz
> 
> Fatal trap 18: integer divide fault while in kernel mode
> cpuid = 0; acpi id = 00
> ...
> panic: integer divide fault

Unfortunately, there are CPU models around that have MSR_PERF_STATUS
bits that are inconsistent, e.g:

- The low and high multipliers (bits 31:24 and 15:8) are equal, so if
  you subtract them and then divide... boom :) 
- Either the low or high multipliers (or both) are zero, which is also
  not good, at least not with the current code.

As an example, I originally added some multiplier sanity checks here:
http://www.openbsd.org/cgi-bin/cvsweb/src/sys/arch/i386/i386/est.c#rev1.27