2002 - cesnet

the use of 158 processors). When we made use of the Network MPI, FLUENTstarted up in this metacomputer configuration in several minutes. However, thenegative aspect is the longer period of a single iteration, lasting 49 seconds insteadof 44 seconds (sockets).The two Tables show partial results for the extensive tasks, with 13 millioncells – car airflow.Notes to Table 7.1: For the number of 8–32 processors, measurements are carriedout at the nympha cluster (Plzeň), for 8–15 processors per singleCPU on a machine, and further on with the use of both machine processors.Note 1: For 32–158 processors, there are 4 parts of the cluster nympha,minos, skurut, skirit, always evenly distributed number of allocatedcomputing nodes.Note 2: This configuration is 16 machines by two processors at each ofthe nympha, minos and skurut clusters.Note to Table 7.2: For 32–158 processors, there are 4 parts of the cluster nympha,minos, skurut, skirit, always evenly distributed number of allocatedcomputing nodes.We see that the use of Myrinet for the nympha cluster is negligible for a smallnumber of CPUs, unlike with a higher number of CPUs (the difference is obviousalready with 20 CPUs), when communication is likely to increase during thecomputation. We have seen the influence of Myrinet when monitoring the timeof task loading to a metacomputer, which is up to two times shorter. As regardsthe overall computing time, this is a marginal aspect.The Network MPI (i.e., use of MPI through the entire distributed system – withthe use of LAM implementation) is worse as regards both task loading and thecomputation itself. The only positive aspect is the FLUENT start-up time, whichis considerably better compared to the socket communication. This is againa rather negligible advantage with respect to a “reasonable” number of CPUs(approx. up to 40) and a usually demanding task (i.e., a task computed over aperiod of several days).Due to the low number of measurements, we are unable to formulate moreprecise conclusions and recommendations – this will be the goal of our effortsin the first half of 2003.In conclusion, we would like to point out that even a part of a PC cluster, i.e.,16 dual-processor nodes with 16 GB memory, can be used as a powerful toolfor highly demanding CFD tasks. The positive aspect is also the possibility ofusing a supercomputer for the definition of extensive tasks – in come cases, it isimpossible to prepare tasks directly in the parallel run of FLUENT (this sectionhas not been parallelized).High-speed National Research Network and its New Applications 2002105