Bug#496850: linux-image-2.6.18-6-486: bogomips reduced from 100 to 20 after package upgrade

[Moritz Muehlenhoff <jmm@inutil.org>]

On Wed, Aug 27, 2008 at 11:23:11PM +0000, Kevin Rolfes wrote:
> Package: linux-image-2.6.18-6-486
> Version: 2.6.18.dfsg.1-22etch2
> Severity: minor
> 
> 
> I think this is minor, but it caught my attention and I thought the
> package maintainer might want to know about it. Upgrading this
> package from 2.6.18.dfsg.1-22 to 2.6.18.dfsg.1-22etch2 caused the
> bogomips benchmark to drop from 99.07 to 20.03 on a Vortex86SX
> based computer.
> 
> Downgrading this package back to 2.6.18.dfsg-1-22 (using
> "apt-get install linux-image-2.6.18-6-486=2.6.18.dfsg.1-22"),
> and changing nothing else, restored the bogomips rating back to 99.07.
> 
> I do not know if the computer actually ran slower. I didn't notice
> a difference while using it, it was just the bogomips number that
> caught my attention. If additional testing would be helpful, please
> suggest something that would run on a minimal (command-line only) Etch
> installation.
> 
> The computer is an Ebox 2300SX, which is a tiny x86 computer that 
> contains a Vortex86SX processor running at 300MHz. (More CPU info at 
> http://www.dmp.com.tw/tech/vortex86sx/)
> I installed Debian Etch 4.0.r4 which came with version 
> 2.6.18.dfsg.1-22 of the package linux-image-2.6.18-6-486. During 
> startup, the computer reported 99.07 BogoMIPS which was in line
> with other reported ratings (i.e. 1/3 the processor clock).
> 
> After the installation, I added security.debian.org to
> /etc/apt/sources.list and used apt-get to upgrade the installed
> packages. According to the time stamps of the installed files
> and the log files, it was the next reboot that showed the 
> reduced BogoMIPS.
>  
> Here is /proc/cpuinfo with the rolled back (2.6.18.dfsg.1-22)
> version of linux-images:
> 
> processor       : 0
> vendor_id       : unknown
> cpu family      : 4
> model           : 0
> model name      : 486
> stepping        : unknown
> fdiv_bug        : no
> hlt_bug         : no
> f00f_bug        : no
> coma_bug        : no
> fpu             : no
> fpu_exception   : no
> cpuid level     : -1
> wp              : yes
> flags           :
> bogomips        : 99.07

Does this error still occur with more recent kernel versions?

If you're running Etch, could you try to reproduce this bug
with the 2.6.24 based kernel added in 4.0r4?
http://packages.qa.debian.org/l/linux-2.6.24.html

Cheers,
        Moritz