Performance comparision of a XP1000 6/500 and GS140 6/525

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Date: Thu, 23 Dec 2004 13:24:14 +0100
To: Tru64 UNIX <tru64-unix-managers@ornl.gov>

Hi managers,

merry christmas to all, whoever will celebrate it.

I've come across the following performance question:

I have a XP1000 6/500, 2GB mem, OS v5.1 and a GS140 6/525, 8 CPU, 8GB mem
(1x4GB, 2x2GB), OS v5.1b.

The GS140 is an upgraded 8400 that now calls itself a GS140 (I did the upgrade
from a AS8400 5/300 to a AS8400 6/525 by replacing the required CPU modules
E2054 -> E2063 and other, now the console says GS140).

The GS140 is dedicated to number crunching of medium sized CFD modells (up to
256MB data). The CFD code can not be run multithreaded or in a MPI
environment. Since the number of simulations to be carried out exceeds 20 I
decided to run 8 simulation simultaneously on the GS140, so that the total
amount of time that is required is acceptable. Instead of having solved one
simulation in a short time with 2 or 4 CPU's I'll get 8 simulations
calculated at once.

Since the GS140 has plenty of mem (for 8 simulations I'll need something
around of 4 GB) and I will make sure that there will be running only one
simulation per CPU I expected no performance degradation.

Since the XP1000 is equipped with nearly the same CPU as the GS140 I checked
the run time of the same modell on the XP1000 while the GS140 was loaded with
7 other simulations (a total of 8 on the GS140). I expected that the run time
of the simulation on the GS140 may be a little bit higher when compared to
the XP1000 (mem access of one CPU on the GS140 may be delayed due to
concurrent access of another CPU). But the delay shouldn't increase the
processing time considerably.

But to my surprise the GS140 needed 4 times the amount of processing time
compared to the XP1000. I was astonished that the processing time increased
that much. Right after having the GS140 up and running I loaded only one
simulation on the GS140 and I seem to remember that the processing time was
comparable to the XP1000 then. Right now there are 8 simulations running and
I'm reluctant to kill them, even though they aren't performing optimal,
because the simulations will end by the weekend. Furthermore I'm not certain
what measures to use to increase the performance of the GS140,

I'm not new to Tru64 but fairly new to the midrange AlphaServers (8400/GS) and
have no experience what may be expected in the situation I'm facing here.
My questions are related to the performance:

Do I have to live with this performace decay, when the GS is fully loaded with
these CPU and mem demanding processes?

Will simultaneous access of the CPU's to the mem decrease the performance that
much?

If I use collect or the other tools may the performance be increased
considerably?

TIA

-- 
Uwe Lienig
----------
fon: (+49 351) 462 2780
fax: (+49 351) 462 3476
mailto:uwe.lienig@fif.mw.htw-dresden.de
Forschungsinstitut Fahrzeugtechnik
<http://www.fif.mw.htw-dresden.de>
parcels: Gutzkowstr. 22, 01069 Dresden 
letters: PF 12 07 01,    01008 Dresden
Hochschule für Technik und Wirtschaft Dresden (FH)
Friedrich-List-Platz 1, 01069 Dresden

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