atexpert predictions and actual performance on the Cray-2

[Hemant Dandekar]

Hi,
     I am trying to run a program written in Fortran on a Cray-2 running
UNICOS 6.1 and CF77.4.0.3 under autotasking. Using the option -Wu"-p"
and running my code in time share mode I generate the output which can
be used by 'atexpert' a autotasking tool. The 'atexpert' tool predicts
the speedup of the code in 'standalone' mode based on the information it
is fed. However, I get very poor speedup compared to the predictions
when I run my code on a 4 processor Cray-2 at NCSA. Here is a comparison
between predicted and actual values. 


# of CPUS           Speedup (atexpert)          Speedup(Actual)
--------------------------------------------------------------------
   1                   1.0                         1.00
   2                   1.9                         1.27
   3                   2.8                         1.32
   4                   3.6                         1.33
--------------------------------------------------------------------


Before I run my code I set my MICRO_NICE value to 0 and my NCPUS value
(these are shell variables) to 1, 2, 3 or 4. I do not set my
MICRO_TIMEOUT variable to a large value as suggested by Dick Steimann,
of CCN Cray Systems group. However, I don't think any of my slave CPU's
remain idle as the breakup of CPU time for a typical run is as follows: 

NCPUS = 3
1 CPU   83.31s
2 CPU   45.76s
3 CPU   26.40s
out of a total CPU time of 155.47seconds.

An obvious way to check things out will be to make another dedicated run
with setting the MICRO_TIMEOUT variable to a large values such as 10000.
However, I cannot make another run for another week. Meanwhile, I would
be curious to know about the experiences of other users on the net with
regards to autotasking on the CRAY-2 under UNICOS 6.0+ and their
experience with 'atexpert' predictions and actual performance. 

Thanks,
hemant

*********
BITNET: V092QGHG at UBVMS.BITNET   |Hemant W. Dandekar             
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         u10978 at u2.ncsa.uiuc.edu|Amherst NY 14260 (716)636-2631(work)

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Bitnet: v092qghg at ubvms.bitnet           | Hemant W. Dandekar
Internet: hemant at asterix.eng.buffalo.edu| 303, Furnas Hall, Chem. Eng.
(716)636-2631                           | SUNY at Buffalo, Buffalo  NY 14260