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2001 Dec 30 17:11

The following is an archive of a post made to our 'vox-tech mailing list' by one of its subscribers.

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Re: [vox-tech] weird boot message
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Re: [vox-tech] weird boot message



On Mon, 29 Oct 2001, Aaron King wrote:
> Been experimenting.  The current working hypothesis is that on reboots
> (warm or cold) when on battery, the CPU is reported as slow.  When
> booting while on AC, the full clock rate is reported. 

This is the "normal" default on many laptops. "You" (generic user)  want
to conserve more power when on battery and suck up the watts when wired.

> I've found a few settings in the BIOS which might affect this
> behavior.  I can set up the power mode for "maximum performance" as
> opposed to "maximum battery life".  I set this to "maximum
> performance" and get full 697 MHz even when booting off the battery.  

Yep, this is one of the BIOS based systems that I was writing about.

> This does not appear to be fully repeatable: I returned the BIOS
> setting to "maximum battery life" and rebooted, /proc/cpuinfo reads
> 697 MHz.

Probably since it was the last default setting, and did not reboot to
re-read the settings that were changed. Probably something decided ~
POST, but read from BIOS. If BIOS is altered after POST, then a reboot
with POST would be needed to re-read the BIOS settings before it could
enable the feature and throttle the CPU. This may not normally happen
(POST) on a "warm" reboot, but only on cold reboots - it depends on the
laptop/machine/vendor/model.

> There is also a "CPU power management" feature in the BIOS which
> apparently "stops the microprocessor clock automatically when there are
> no system activities".

I would not trust that with Linux unless you or someone else has personal
experience with it. It may just be a standby mode which has been known to
work on many linux based laptops, but also break on a few models of
laptops.
 
> But first things first: is there any reason to believe this is something
> I should worry about?

(not being coy, or agressive here, just informal/relaxed)
Well... worry? Slower CPU = less power and less heat and longer CPU life,
but experience with laptops suggests the CPU is not what fails so much.
(Though some of HP's laptops, and COMPAQs laptops have been known to be so
hot as to power-off the machines while they were running, and this can't
be a good thing for the hardware's life.) For the most part, this means it
is a decision based on performance vs duration (power stored and available
in battery.) You want it to run faster (burn brighter by burning the
candle at both ends) or last longer (not have as much light but last
longer)? [I am not talking about life of the machine here so much as the
battery unless your laptop powers down after being on too long and unable
to dissapate the heat.]

> Might I be taking a performance hit for the life of the session?  

This seems likely. The CPU would actually be running slower, cooler, and
using less power. This would mean programs would be running slower too.

> What depends on /proc/cpuinfo?

I think (anyone, please correct me) the information is /proc/cpu is kernel
probed and read initially at boot time. Not sure if it is updated when the
CPU changes (never had to wory about this/check it) but why not see if it
does if you decide to alter your CPU's speed while running the OS.

I am not sure anyone has coded much of anything depend upon /proc/info
except fro some CPU performance goodies (little aps that tell you about
your CPU in a nifty GUI - much of the information available to you by
looking from a console as /proc/cpu and/or uptime / top.)

You may want to check out the latest version of apmd to see if it can talk
to your hardware and throttle the CPU's speed while it is running and
alter the settings of the speed of the system. I do not know the status of
this in apmd or how (well) it works with linux on *this* feature, but I
used it for a long while on one of my laptops wayyyy back and found its
other features were good. Another tool that is/was good is/was hdparm for
disk spin down and other nifty features.

-ME

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     Systems Department Operating Systems Analyst for the SSU Library



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