Re: Stealing ur megahurts (no, really)

John Richard Moser
2006-05-19T17:28:29Z

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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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