Re: Stealing ur megahurts (no, really)

[Antonio Vargas]

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..)
> >
>
> <snip>

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
algorithms


--
Greetz, Antonio Vargas aka winden of network

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