From: Steven Ericsson Zenith <zenith@kai.com>
Subject: Re: Linda / The Parform 
Organization: 	Kuck and Associates, Inc.
		1906 Fox Drive, Champaign IL USA 61820-7334,
		voice 217-356-2288, fax 217-356-5199
Date: Fri, 18 Dec 92 14:10:14 -0600


I find these numbers difficult to believe.

     >  Procs  POSYBL	SCA linda	PVM	MC-2	The Parform
     >    1	1370.6	1370.6         1370.6	 --	1370.6 (1.0)*
     >    2	 737.2	 662.2 		648.0	 --	 654.8 (2.1)
     >    4	 442.6	 342.6 		328.0	 921.4	 332.3 (4.1)
     >    6	 339.3	 235.5 		219.0	 618.5	 221.7 (6.2)
     >    8	 284.6	 175.8 		168.4	 466.7	 170.2 (8.0)
     >   10	 260.2	 144.3 		143.6	 376.6	 137.4 (10.0)
     >   12	 244.7	 122.1 		116.6	 318.2	 116.0 (11.8)
     >   14	 242.7	 104.5 		100.1	 276.2	 103.5 (13.5)
     >   16	 239.5	  92.8 	 	 90.0	 240.0	  89.0 (15.4)
     >   18	 242.6	  84.5 		 97.5	 215.9	  80.9 (16.9)
     >   20	 241.6	  76.0 		 85.8	 196.6	  73.5 (18.7)
     >   22	 	  71.5	 	 68.5	 182.8	  67.5 (20.3)
     >   24		  66.5	 	 63.6	 170.9	  62.5 (21.9)
     >   26		  63.1	 	 60.5	 160.9	  58.6 (23.4)
     >   28		  58.5	 	 56.7	 151.9	  55.8 (24.7)
     >   30		  55.1	 	 53.5	 144.7 	  53.0 (25.9)
     >   32		  54.0	 	 54.0	 138.5	  51.0 (26.9)
     >   34		  52.4	 	 54.0		  50.8 (27.0)
     >   36		  51.4	 	 52.0		  48.5 (28.3)
     >   38		  51.3	 	 54.0		  48.4 (28.3)
     >   40			 	 52.9		  47.2 (29.0)
     > 
     >    * speedup in parentheses

Firstly, bells start ringing for the single processor case.  Why?
Because they are all the same and to my knowledge these systems don't
all use the same compiler.  I expect to see some variation.
No indication is given of what the 1 processor time means - is this the
sequential execution time under the respective system compiler?  It
should be. The above numbers can only begin to make sense if the base
compiler *is* the same in all cases - otherwise we do not know what we
are comparing.

I would like to see the superlinear speed up explained. It's difficult
to assess without a detailed description of the hardware, operating
system infrastructure, etc.. 

Since this problem is obviously more than embarrassingly parallel I'd
like to know how much, if any, of the interaction mechanism was used
during computation. If the answer is, as I suspect, that after the data
and work distribution, insignificant interaction took place then the
above tells us something about the parallel decomposition of the problem
but sweet Fanny Adams about any of the systems tested.

What was measured here? Does the clock start before or after
distribution of the data set and processes?

I know people love to see numbers like this, it makes them feel cosy and
all warm inside but most such statistics - in this particular area and
that I've seen - belong in the marketing department.

Here's a test that might tell you something about each of the systems:
using the same base compiler, hardware and operating system plus a
library implementing each model tell me (scaling over the same number of
processors shown above) the execution times taken to perform a 1024x1024
matrix transpose where each element of the matrix is a double float
assigned the value of its initial index.  ;-) ( <- wicked grin). A
second test is to do the above and print the before and after result ;-)
(( <- a double wicked grin).

And even if you did this, unless you can show that the implementations
are truely comparable, (i.e., they use the same implementation
techniques and infrastructure) it will not tell you anything about the
model's performance. That leaves you with a serious logistical problem -
one I had to confront and failed to fund in the Ease work - you have to
personally undertake the implementation of each model in a uniform (dare
I say "scientific") way - any other comparison is meaningless.

One qualitative - and alas subjective - comparison can be made without
execution. That is to look at the expressiveness of the solution. And no
matter how I may criticize Linda's other idiosyncrasies (Who me?),
"Message Passing Style" sucks in this respect for any nontrival problem.

     >  -------------------------------------------------------------------
     >  Clemens Cap				email: cap@ifi.unizh.ch
     >  Volker Strumpen                        email: strumpen@ifi.unizh.ch

Steven Ericsson Zenith
--
Steven Ericsson Zenith
Disclaimer: Opinions expressed are my own and not necessarily those of KAI.





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