Gnome and task execution timing

[don fisher]

I am running a code to locate Near Earth Objects in astronomical CCD 
images. One element of the pipeline is a package called sextractor, that 
is also available as a deb package.

I am running Ubuntu 8.10.

My problem is that running gdm/gnome desktop appears to cost a factor of 
two in execution time. I have an 8 processor 16 core Opteron system with 
32GB of ram. I would not have expected my application to be in 
competition with the gnome/gdm. And I could seen no competition with 
free or xosview tools. The code is executed from a remote machine via 
ssh, so there is no activity required by the local X environment.

The following is the output from sextractor taken under gnome/gdm, then 
rebooted under fvwm.

Under gnome/gdm:
----- SExtractor 2.5.0 started on 2009-03-13 at 14:51:25 with 1 thread

Measuring from: "N26045"  / 4110 x 4096 / 16 bits INTEGER data
Weighting from: "N04053"  / 4110 x 4096 / 32 bits FLOATING POINT data
(M+D) Background: 1233.26    RMS: 18.2807    / Threshold: 19.1947
Objects: detected 65608    / sextracted 50033
 > All done (in 66 s)

61.635u 4.456s 1:06.08 100.0%   0+0k 0+10848io 0pf+0w

Under fvwm:
----- SExtractor 2.5.0 started on 2009-03-13 at 15:05:58 with 1 thread

Measuring from: "N26045"  / 4110 x 4096 / 16 bits INTEGER data
Weighting from: "N04053"  / 4110 x 4096 / 32 bits FLOATING POINT data
(M+D) Background: 1233.26    RMS: 18.2807    / Threshold: 19.1947
Objects: detected 65608    / sextracted 50033
 > All done (in 30 s)

26.821u 1.772s 0:29.98 95.3%    0+0k 199480+10848io 10pf+0w

The user time under gnome is 61.635, under fvwm is 28.821. What can 
gnome/gdm be doing to slow down this application. Examination of 
/proc/cpuinfo reveals the same cpuspeed etc. for both runs.

Please offer suggestions.

don
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