Re: Stealing ur megahurts (no, really)

From: Antonio Vargas
Date: Sat May 20 2006 - 14:48:46 EST

On 5/19/06, Joel Jaeggli <joelja@xxxxxxxxxxx> wrote:
Matti Aarnio wrote:
> On Fri, May 19, 2006 at 02:13:02AM -0400, John Richard Moser wrote:
> ...
>> On Linux we have mem= to toy with memory, which I personally HAVE used
>> to evaluate how various distributions and releases of GNOME operate
>> under memory pressure. This is a lot more convenient than pulling chips
>> and trying to find the right combination. This option was, apparently,
>> designed for situations where actual system memory capacity is
>> mis-detected (mandrake 7.2 and its insistence that a 256M memory stick
>> is 255M....); but is very useful in this application too.
>> 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.
> ...
>> Questions? Comments? Particular ideas on what would happen?

The other thing I would observe is that clock speed is only part of the
equation, it's one thing to soak up some cpu cycles, but the cpu may be
a lot more superscalar (pipelineing, simd instructions, multiple cores
etc) than the one you're trying to simulate, probably it also has a lot
more cache and much faster memory. So that while you can certainly soak
up a lot of cpu pretty easily there are other considerations that might
effect simulating the performance of say a 100mhz pentium on say an
athlon 64x2.

emulation would probably go a lot further as an approach

> Modern machines have ability to be "speed controlled" - Perhaps
> they can cut their speed by 1/3 or 1/2, but run slower anyway
> in the name of energy conservation.
> Another approach (not thinking on multiprocessor systems now)
> is to somehow gobble up system performance into some "hoarder"
> (highest scheduling priority, eats up 90% of time slices doing
> excellent waste of CPU resources..)


what is really needed is to be able to throttle the memory latency and
bandwith.. even with +++Ghz processors if there is no memory speed all
the rest lacks... this would enable better testing of memory intensive

Greetz, Antonio Vargas aka winden of network

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