what is a flop (Roberto Ammendola)

Maurice Hilarius maurice at harddata.com
Tue Jun 17 16:01:32 EDT 2003

With regards to your message at 01:01 PM 6/17/03, 
beowulf-request at scyld.com. Where you stated:
>  Date: Tue, 17 Jun 2003 20:34:48 +0200
>From: Roberto Ammendola <roberto.ammendola at roma2.infn.it>
>Subject: Re: what is a flop
>Saurav Gohain wrote:
> >
> > From a beowulf pdf tutorial, i came to know that it is calculated as
> > Total Peak Performance= No of Nodes * No of CPU's * Floating point
> > operations per second * No of Cycles per second.
> >
>I would say:
>Total Peak Performance= No of Nodes * No of CPU's per Node * Floating
>point operations per clock cycle * No of Cycles per second.
>The "Floating point operations per clock cycle" depends on the
>processor, obviously, and on which instructions you use in your code.
>For example in a processor with the SSE instruction set you can perform
>4 operations (on 32 bit register each) per clock cycle. One processor
>(Xeon or P4) running at 2.0 GHz can reach 8 GigaFlops. But this is only
>a peak performance. The real value is up to the cleverness of the
>programmer ;)

And I would say dual CPU boards do not sale at a factor of 2:1 over singles.
This is mainly ruled by 3 things:
1) efficiency of chipset for SMP operations, access to memory, buses, etc..
2) efficiency of compiler at SMP/multithreaded code generation
3) efficiency of code design to complement the above factors.

As a general ( really general as it changes a lot with code and compilers) 
the rule I know :

Dual P3 ( VIA chipset): 1.5 : 1
Dual XEON P4 ( Intel 7501 chipset): 1.3 : 1
Dual AthlonMP ( AMD 760MPX chipset) 1.4 : 1
Dual Opteron (AMD 8xxx Chipset) 1.8 : 1
Dual Alpha (DEC Tsunami chipset) 1.8 : 1

With our best regards,

Maurice W. Hilarius       Telephone: 01-780-456-9771
Hard Data Ltd.               FAX:       01-780-456-9772
11060 - 166 Avenue        mailto:maurice at harddata.com
Edmonton, AB, Canada      http://www.harddata.com/
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