CCL: Changing SYSV parameters for parallel GAMESS

 Dear Collegues,
 I recently installed and ran parallel GAMESS using DDI on a 2CPU Xeon machine
 with hyperthreading (4 virtual CPU's).  I ran through the entire included test
 set using 4, 2 and 1 cpus and found interesting results for the timings.  The
 time to run gamess seemed to be by far lowest with 1cpu, and 2,4 cpus scaled
 about linearly against each other.  However, running on 2 or 4 nodes resulted in
 very, very low cpu usage (<10%) and longer cpu and wall times.  At this point
 I extended the sysV shared memory from 33MB to 1GB, thinking that this was why
 there was no improvement in time with parallel use.  What I found after this was
 that 1) the computer was significantly slowed down for everything, even mundane
 tasks 2) the cpu usage was marginally improved for 2 & 4 node use, but was
 reduced for 1 node use 3) the wall time was made longer in all cases and had no
 obvious correlation with the number of nodes used.
 Can any of the discussion group member shed light on these observations?  Should
 I have increased the SYSV shared memory?  Should I increase the number of
 semaphores as well?  What kind of improvements should I expect using parallel
 Seth Olsen
 Dr Seth Olsen, PhD
 Postdoctoral Fellow, Computational Systems Biology Group
 Centre for Computational Molecular Science
 Chemistry Building,
 The University of Queensland
 Qld 4072, Brisbane, Australia
 tel (617) 33653732
 fax (617) 33654623