[Beowulf] Execution time measurements - clarification

[Mark Hahn]

From: Mikhail Kuzminsky <mikky_m at mail.ru>
Subject: [Beowulf] Execution time measurements - clarification

Dear Mark, could you pls forward my message to beowulf at beowulf.org (because my messages as before can't be delivered to maillist) ? It's clarification of my previous question here.

Mikhail
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I have strange execution time measurements for CPU-bound jobs (to be exact, Gaussian-09 DFT frequency

calculations). Results are strange for *SEQENTIAL* calculations !

Executions were performed on dual socket Opteron 2350 (Quad core) server worked under Open SuSE Linux

10.3.

When I run 2 identical examples of the same batch job simultaneously, execution time of *each* job is

LOWER than for single job run !

I thought that it may be wrong "own for G09" times, so I checked their via time:
(time g09 *pair1.com) >&testt1 &
etc 
But this confirms strange results:

For pair of simultaneously running sequential jobs

88801.141u 52.475s 24:40:57.58 99.9%    0+0k 0+0io 1221pf+0w
88901.996u 13.472s 24:41:53.97 100.0%   0+0k 0+0io 0pf+0w


For run of 1 example of the same sequential job

100365.236u 27.297s 27:53:13.53 99.9%   0+0k 0+0io 1pf+0w

Is there any ideas why this situation might be ?

Mikhail Kuzminsky