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Subject: Re: Stealing ur megahurts (no, really)
Date: Fri, 19 May 2006 07:43:47 -0400
Message-ID: <Pine.LNX.4.61.0605190740090.13794@chaos.analogic.com>
In-Reply-To: <20060519112218.GE19673@gallifrey>
Thread-Topic: Stealing ur megahurts (no, really)
Thread-Index: AcZ7OX3siyelW13VTQW8P3HD2bNSSg==
References: <446D61EE.4010900@comcast.net> <20060519112218.GE19673@gallifrey>
From: "linux-os \(Dick Johnson\)" <linux-os@analogic.com>
To: "Dr. David Alan Gilbert" <linux@treblig.org>
Cc: <linux-kernel@vger.kernel.org>,
       "John Richard Moser" <nigelenki@comcast.net>
Reply-To: "linux-os \(Dick Johnson\)" <linux-os@analogic.com>
Sender: linux-kernel-owner@vger.kernel.org
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On Fri, 19 May 2006, Dr. David Alan Gilbert wrote:

> * John Richard Moser (nigelenki@comcast.net) wrote:
>
>> Scrambling for an old machine is ridiculous.  Down-clocking makes sense
>> because you can adjust to varied levels; but it's difficult and usually
>> infeasible.  Pulling memory and mix and matching is not much better.
>
> <...>
>
>> This brings the idea of a cpumhz= parameter to adjust CPU clock rate.
>> Obviously we can't do this directly, as convenient as this would be; but
>> the idea warrants some thought, and some thought I gave it.  What I came
>> up with was simple:  Adjust time slice length and place a delay between
>> time slices so they're evenly spaced.
>
> <...>
>
> Hi John,
>  While cpu downclocking helps a bit, it would be hopelessly inaccurate
> for figuring out if your app would run fast enough on the given
> ancient machine.  A lot else has happened to the world since the days
> of the 200MHz CPU:
>    * Faster memory
>    * Larger caches
>    * Faster PCI busses
>    * Instruction set additions (various more levels of SSE etc)
>    * Faster discs
>    * Changes to the CPU architecture/implementation
>
> Still, it would be interesting to see the difference in performance
> of a downclocked modern processor and its 10 year old clock equivalent.
>
> Dave
>
> --
> -----Open up your eyes, open up your mind, open up your code -------
> / Dr. David Alan Gilbert    | Running GNU/Linux on Alpha,68K| Happy  \
> \ gro.gilbert @ treblig.org | MIPS,x86,ARM,SPARC,PPC & HPPA | In Hex /
> \ _________________________|_____ http://www.treblig.org   |_______/
> -

You can readily slow down a machine by creating a bunch of tasks
that just do:

int main() {
 	for(;;)
           ;
}

They will use their entire time-slice until preempted. You want
it slower, create more such tasks. FYI, `top` should show them
all getting the same amount of CPU time. If they don't the
scheduler is broken!

Cheers,
Dick Johnson
Penguin : Linux version 2.6.16.4 on an i686 machine (5592.89 BogoMips).
New book: http://www.AbominableFirebug.com/
_


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