Athcool does cut the idle temperatures of the nodes considerably, but
apparently also prevents them from performing this sort of transfer at full
speed, whether or not buffer is used.
Well, near the top of the athcool website there is a warning and one the
listed items is 'a slowdown in harddisk performance' - so nothing new here
;-)
athcool works by putting the cpu-northbridge interface into a low-power mode.
the difficulties people had with it was that this sort of down-clocking
was new at the time, and not well-handled by all chips, probably on
both the chipset and cpu sides. erata centered on how long it took to
stabilize the PLL's involved.
things are quite different nowadays - AMD put the northbridge entirely
on-cpu, so it has fully control, and can modulate clocks extensively
and differentially. I don't know how common (or effective) it is to modulate
HT power, but such features show up prominently in recent HT revs. it's
interesting to speculate about Intel - mostly it solved this by dominating
the chipset market for its own CPUs. I'm guessing Intel will fall somewhat
behind AMD in system-wide power savings, at least until CSI. even then,
I'm a little unclear how good Intel's initial implementation will be -
the fact that they've chosen to not simply adopt HT indicates to me that
Intel will be re-learning AMD's lessons.
Which is interesting because it didn't have any measurable effect on CPU
bound processes. I had thought it would shut itself off and get out of the
I'd expect athcool to not affect a cache-friendly cpu-bound process,
but to hurt pretty badly if you have cache misses. networking (using the
normal network stack) count as memory-bound, I think, rather than kinds
of IO which might be more DMA-intensive. that is, if a disk is streaming
many MB into memory, the CPU's northbridge interface should be able to
go low-power (though most disk transfers are only in the 64K range...)
regards, mark hahn.
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