Cheap PCs from Wal-Mart
hahn at physics.mcmaster.ca
Mon Jun 2 19:36:29 EDT 2003
> I went to the linked page at Toms Hardware and found reasonably close results
> Athlon XP 3200+, and P4 3GHz...
right, as I said "high-end".
> Now, what's the power consumption of those two?
> I think the P4 dissipates a max of 85W (poking around on the same Tom's page)
that would be max TDP.
> The C3 at 800 MHz dissipates 6.65W average and peaks at 12W
> The Nehemiah at 1 GHz dissipates 11.25/15 W ave/pk
I suspect VIA's "peak" is not equivalent (lower) than Intel's TDP.
> So, looking at the scaling and comparing P4 against Via C3 Nehemiah
> Speed 6809/1591 4.3:1
> Power 85/15 5.7:1
> So the Via looks like it does more computes/Joule...
well, for dhrystone at least. which isn't really surprising if you
think about the fact that dhry is entirely on-chip, and much of
the power dissipated by a high-end CPU is actually the external
if you consider a *real* workload which has some external load,
you'd see much higher throughput on the thick system.
> This is really a first order approximation. You'd have to look at
> peripheral power, memory power, and power supply conversion and power
> distribution efficiency. Peripherals and memory probably scale with memory
> speed fairly linearly.
huh? do you mean "the P4 drives ram much faster and so the ram
will also dissipate more power"?
> The higher powered device will have more I^2R
> losses in the power supply and distribution. (Supplying 50 or so Amps at
> 2-3V is no easy feat)
well, the PS supplies 3.3V; the Vcc for the CPU only has to travel
a couple of inches, and that's probably in a plane. I don't really
thing that's an issue.
> Here's the upshot... if you're in an environment where ultimate performance
> is important, than you're probably best going with as few big fast
> processors as you can get (the original Cray paradigm). On the other hand,
> if you're in an environment where maximizing computation for a fixed amount
> of power/heat dissipation resources (i.e. spaceflight or portable
> operation), then things like the Via C3 start to look attractive, assuming
> your task scales well.
almost tautological, it's so unobjectionable ;)
my whole point was that people must not even start to think that
these low-power CPUs are close in performance. and even if they were,
I don't think people really have an intuitive sense for what "scales well"
means - I doubt *anyone* has a task that is as undemanding of the system
as dhrystone is, for instance.
> computing, I'd like to see more attention paid to computing per joule or
> computing rate/watt. There are different tradeoffs whether you are
sure, but please, let's use specFPrate per watt. even that's a bit
dated, since it's so cache-friendly.
but the real question is: can you afford to use a cluster node which
has, say, 10-20% of the performance? you can stretch Amdahl's law a bit
and see that the further you push wimpy nodes, the smaller a problem
domain you can address (requires ever looser coupled programs, longer
latency of individual work-units, etc).
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