[Warewulf] Re: [Beowulf] hpl size problems

Andrew Piskorski atp at piskorski.com
Mon Sep 26 16:01:06 EDT 2005


On Mon, Sep 26, 2005 at 03:43:00PM -0400, Andrew Piskorski wrote:

> It's amusing that Mark Hahn is already participating in this thread,
> because his post to the Beowulf list gave a link explaining a detailed
> real-world example of that effect very nicely:
> 
>   http://www.beowulf.org/archive/2005-July/013215.html
>   http://www.sc-conference.org/sc2003/paperpdfs/pap301.pdf

Hm, looking at it again reminds me that Petrini, Kerbyson, and Pakin's
paper is much more general than I implied.  E.g., their "Finding #4"
is:

  "Substantial performance loss occurs when an application resonates
  with system noise: high-frequency, fine-grained noise affects only
  fine-grained applications; low-frequency, coarse-grained noise
  affects only coarse-grained applications."

They also mention that LINPACK is coarse-grained with not that much
communication, so I guess my naive assumptions about HPL were wrong.
Hm, no doubt Mark H. knew that, which is why he didn't immediately
jump on the "Warewulf is faster because it eliminates the
jitter-causing daemons" hypothesis.

-- 
Andrew Piskorski <atp at piskorski.com>
http://www.piskorski.com/
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