John/All,
It is a useful reminder I guess, but I have to assume that this is
something that folks on this list are familiar with, No? State is
more complicated for parallel work and less deterministic. As
these qualities accumulate in the processing of any workload
a stochastic outcome (timings in this case, but it can also effect
precision as anyone that has compare vector to scale results
remembers) is the result.
This effect is another manifestation of the behavior demonstrated
by Galton in the late 1800s when he dropped English pence
through a pinned board (the pins are the identical cores, the pence
parrallel processes) ... he got a gaussian distribution. As the article
suggests you can reduce the variance by limiting the non-determinism
in process and that is what eXludus (a Montreal based software scheduling
company) is doing at the job and process level. As the number of
of cores and/or number of processes (virtual or otherwise) grows
so does the variance in outcomes. This is a on-die manifestion of
job skew is it not, and another of the second law of thermodynamics ...
rbw
----- Original Message -----
From: "John Hearns" <hear...@googlemail.com>
To: beowulf@beowulf.org
Sent: Tuesday, December 23, 2008 6:54:39 AM GMT -05:00 US/Canada Eastern
Subject: [Beowulf] Not all cores are created equal
I'm surprised this has not been flagged up yet. Shamelessly passed on from
Slashdot:
http://www.gcn.com/online/vol1_no1/47765-1.html
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