Re: Stealing ur megahurts (no, really)

From: linux-os (Dick Johnson)
Date: Fri May 19 2006 - 07:43:30 EST

On Fri, 19 May 2006, Dr. David Alan Gilbert wrote:

> * John Richard Moser (nigelenki@xxxxxxxxxxx) 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 @ | MIPS,x86,ARM,SPARC,PPC & HPPA | In Hex /
> \ _________________________|_____ |_______/
> -

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

int main() {

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!

Dick Johnson
Penguin : Linux version on an i686 machine (5592.89 BogoMips).
New book:

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