Message-ID: <446DFF25.4020301@comcast.net>
Date: Fri, 19 May 2006 13:23:49 -0400
From: John Richard Moser <nigelenki@comcast.net>
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To: "Dr. David Alan Gilbert" <linux@treblig.org>
CC: linux-kernel@vger.kernel.org
Subject: Re: Stealing ur megahurts (no, really)
References: <446D61EE.4010900@comcast.net> <20060519112218.GE19673@gallifrey>
In-Reply-To: <20060519112218.GE19673@gallifrey>
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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
> 

Skews and fuzz.  Imperfections, but at least we get a general idea.  ;)

> Still, it would be interesting to see the difference in performance
> of a downclocked modern processor and its 10 year old clock equivalent.
> 

Yes.  Too bad CPUs can't be uniformly underclocked by design; they have
at most 3-5 different levels of CPU frequency you can pick from at run time.

> Dave
> 

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