[Warewulf] Re: [Beowulf] hpl size problems

Greg M. Kurtzer gmk at runlevelzero.net
Mon Sep 26 16:18:03 EDT 2005


On Mon, Sep 26, 2005 at 04:01:06PM -0400, Andrew Piskorski wrote:
> 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.

I snipped out a bit of content above which may have led to a
misunderstanding... The application that got the 30% speed up was not
the HPL, rather a geophysics application (developed in house) which
IIRC does barrier quite a bit and is high-frequency/fine-grained.
Your assumption seems accurate indeed. ;)

Actually, our HPL speedup was not as significant. The fastest previous
configuration (as Dell mentioned to us) was 81%, and we got 83.4%. With
that said, our system had faster CPU's but the same bus speeds as the
previous record holder which even makes it more remarkable that we
obtained a higher efficiency.

Thanks for the link to the PDF!

-- 
Greg M. Kurtzer
http://runlevelzero.net/
http://caosity.org/
http://warewulf-cluster.org/

Do not look anywhere for truth, for all that is needed is to refrain from
allowing concepts to arise.
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