Dear Roy, On Tue, 7 Apr 2009, Roy Stogner wrote:
> My last reservation: is there any performance penalty? The ghosted > vectors should be more scalable than serial vectors on N processors, > but they've got overhead that may cost CPU time on 2-4 processors. > When you were regression testing those residuals, did you happen to > take any timing data? Yes, unfortunately, I did, but I didn't look at them up to now. The reason is that, when I started my application in the morning, it was in no case finished before I knocked off work, but it was in all cases finished on the next morning. So my intuition was that it was equally fast. But I forgot that there is a wide range within that. Here's the result (hh:mm:ss): no-ghosted-1 : 11:34:10 no-ghosted-2 : 11:35:54 ghosted-1 : 17:25:28 ghosted-2 : 16:33:23 That was with 8 CPUs each. Quite disappointing. On the other hand, using ghosted vectors would allow my application to use more CPUs without actually using more computing resources (because each node of the cluster has 8 CPUs, but without ghosted I couldn't use more than 3 for memory reasons). What do you think, should I perform another two computations with 24 CPUs (on three nodes) and see how fast that is? (Remark: You certainly notice that 8 is not divisible by 3, so that 8 CPUs with 3 per node doesn't make sense. What I did was 2*3+1*2 CPUs, which is of course not efficient, but the point is that I originally started with 2*4 CPUs, but that turned out to sometimes (depending on the input configuration) run out of memory, so I required more nodes, but didn't want to change the total number of CPUs because that might have slightly changed the results.) Best Regards, Tim -- Dr. Tim Kroeger tim.kroe...@mevis.fraunhofer.de Phone +49-421-218-7710 tim.kroe...@cevis.uni-bremen.de Fax +49-421-218-4236 Fraunhofer MEVIS, Institute for Medical Image Computing Universitaetsallee 29, 28359 Bremen, Germany ------------------------------------------------------------------------------ This SF.net email is sponsored by: High Quality Requirements in a Collaborative Environment. Download a free trial of Rational Requirements Composer Now! http://p.sf.net/sfu/www-ibm-com _______________________________________________ Libmesh-devel mailing list Libmesh-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/libmesh-devel
