Subject: Gaussian98w and SMP processing

From: "Armando Navarro" <[email-masked]>
Date: Thu, 2 Mar 2000 19:34:28 +0100

Dear members:
I have a Dual PentiumII PC and after installing PC-GAMESS I gave to the 
system variable named MKL_NPROC the value 2 in order to run GAMESS in
SMP parallel mode.
However I noticed a strange behavior of Gaussian98w after this. The
program seems to use the two CPU, so I thought that Gaussian was
effectively running in SMP mode.
But when I measured the cpu and wall-clock times there was non
improvement respect to set MKL_NPROC=3D1.
Has anybody noticed this behavior of Gaussian in Dual Boxes?
Regards
Armando Navarro
Departamento de quimica Organica
Facultade de quimica
Universidade de Santiago de Compostela
Spain
e-mail: [email-masked]

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From: "Alex. A. Granovsky" <[email-masked]>
Date: Thu, 2 Mar 2000 23:57:36 +0300

Dear Armando,

> improvement respect to set MKL_NPROC=1.
   It seems that G98w uses old MKL v. 2.0 (or v. 2.1, I'm not sure) 
so it is affected by the MKL_NPROCS environment variable. 
The itself problem is in the MKL v. 2.0/2.1 behavior. 
Namely, the additional thread(s) are not suspended after 
matrix-matrix multiplication. Thus, G98w consumes CPU 
time on all CPUs, while the actual calculations are mainly 
performed only on one CPU. 
  Next, it seems that the average size of matrices used by the 
G98w is relatively small, so there is no benefit due to usage of
second CPU even if performing matrix-matrix multiplication.
   As to the PC GAMESS, we developed a workaround for this 
problem when dealing with old MKL 2.0. Starting from the 
MKL 3.0, the behavior of MKL-created threads was fixed, 
namely, they are suspended if not needed for actual calculations.
Also, if you use PC GAMESS v. 5.3 and higher, the simplest way to
set the number of CPUs used is simply set integer variable  "mklnp" 
in $system group to the desired number of CPUs (it is longer not 
necessary to use MKL_NPROCS with the newer PC GAMESS).

Best regards,
Alex Granovsky

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From: Laurence Lavelle <[email-masked]>
Date: Thu, 02 Mar 2000 13:31:14 -0800

G98W does not use SMP. What your seeing is the OS using one CPU for all 
system management and G98W running on the other. My guess is about 20% CPU1 
and 100% CPU2 respectively.

Yes, it would be nice if G98W ran in SMP mode.

Hope that helps.

At 07:34 PM 03/02/2000 +0100, Armando Navarro wrote:

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Laurence

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Laurence Lavelle, Ph.D.
University of California Los Angeles
Department of Chemistry & Biochemistry and Molecular Biology Institute
Laboratory of Structural Biology & Molecular Medicine
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