[Beowulf] power usage, Intel 5160 vs. AMD 2216

David Mathog mathog at caltech.edu
Thu Jul 12 14:14:48 PDT 2007

"Robert G. Brown" <rgb at phy.duke.edu> wrote 

> Google for a "kill-a-watt".  Brand new, shipped, it's about $25 (from
> e.g. Amazon).  A must have for any serious cluster enthusiast or
> manager -- use it to plug the systems in and then look.  It's one of the
> only ways to be sure.

I'll second that recommendation.  I used one to make a lot of power
measurements on various systems:


One thing it taught me is that screensavers WASTE energy, even ones that 
blank the display.  While that worked ok for CRTs (where power usage
is proportional to screen brightness) it just sets the pixels to black
on an LCD, which saves no energy at all.  Far better to let the
OS put the monitor into standby, where energy usage is roughly zero.

Larry Stewart <larry.stewart at sicortex.com> wrote:

> I do agree though, that if you aren't computing anything, then you
> may as well unplug the machine.

Well, the problem with going from full off to full on is that it's
quite slow. Plus they won't always come back up reliable (Cough, Tyan,
cough).  It would be nice if somebody made a server class
CPU with an ultra low power setting - the system
would still be running, just very, very slowly.  Much faster
kicking up the CPU from 100Mhz to 3Ghz than rebooting the system.  The
normal CPU frequency shifting software could keep an eye on the load
and run as slowly, or as quickly, as is possible/required.   

Also, it's definitely bad to spin disks down and up frequently, but I
think mostly the problem is that the disk goes all the way to,
stopped and bad things tend to happen there.  I wonder if a disk
couldn't be built that could slow down from 10K RPM to 5K RPM
(or less), and save energy that way.  Just keep the platters moving
fast enough to float the heads.  The time to reposition the heads
wouldn't change, although the seek time would be a bit longer waiting
for the right piece of data to rotate around.  Such a disk could
conceivably also monitor its own activity and spin up to full speed
when that is warranted.  With 8Mb buffers being common I suspect that
under a lot of circumstances there would be virtually no difference
between the 5K and 10K modes.

The flip side of all of this is that if the power usage is going up and
down dramatically on the cluster it might cause problems with, for
instance, the room's UPS or A/C.  


David Mathog
mathog at caltech.edu
Manager, Sequence Analysis Facility, Biology Division, Caltech

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