Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!elroy.jpl.nasa.gov!ncar!acd.ucar.edu!pack
From: pack@acd.ucar.edu (Dan Packman)
Newsgroups: comp.benchmarks
Subject: A short io benchmark...
Keywords: How many simultaneous reads are efficient?
Message-ID: <9456@ncar.ucar.edu>
Date: 7 Dec 90 23:38:06 GMT
Sender: news@ncar.ucar.edu
Reply-To: pack@acd.ucar.edu (Dan Packman)
Organization: Atmospheric Chemistry Division/NCAR, Boulder CO
Lines: 47

The following very short benchmark program attempts to measure
raw fortran unformatted io speed.  I can duplicate the program n times
for n tmp files or can run n read programs on a single tmp file.
The tmp file is about 10 megabytes in size.  The 130000 dimension
is representative of some of our applications.
I simply run "simultaneously" via

   % time rd & ; time rd1 & ; time rd2 & ; time rd3 & ; ...

 Running on an IBM RS6000/320 I obtain (in elapsed seconds on an
otherwise unloaded machine):

   \n        |  1   |   2  |   3  |     4   |  5   |  6  |  7  |
__________________________________________________________________
one tmpfle   |      |  31  |  47  |  64     | 80   | 101 | 119 |
_______________16.5_______________________________________________
 n  tmpfles  |      |  36.5|  56  |  86-116 |
__________________________________________________________________

The first test shows remarkable linearity through 7 simultaneous processes.
The second test with multiple files to read shows a falloff (and unequal
times for the processes) for 4 simultaneous processes.  Any comments?
[I would guess that "server" class machines might show slightly
better times for a single read, but would show much better results
for many simultaneous processes.]
=====
       program wr
       double precision a(130000)
       open(1,file='/tmp/tmpfle1',form='unformatted',status='new')
       do 10 i=1,10
         a(130000)=dble(i)
         write(1)(a(ii),ii=1,130000)
 10    continue
       end

       program rd
       double precision a(130000)
       open(1,file='/tmp/tmpfle1',form='unformatted',status='old')
       do 10 i=1,10
         read(1)(a(ii),ii=1,130000)
         if (a(130000).ne.dble(i)) then write(0,100)i,a(130000)
 100     format(' i=',i2,' bad value =',1pd12.5)
 10    continue
       end
Dan Packman     NCAR                         INTERNET: pack@ncar.UCAR.EDU
(303) 497-1427  P.O. Box 3000                   CSNET: pack@ncar.CSNET
                Boulder, CO  80307       DECNET  SPAN: 9.367::PACK