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May 27, 2009, 06:45 |
OpenFOAM machine loads for parallel runs
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#1 |
Senior Member
Rishi .
Join Date: Mar 2009
Posts: 149
Rep Power: 17 |
Hello All,
I have observed that when I use multiple CPUs of the same node is the machine load is quite high (higher than number of proc). In comparison, CFX usually does not behave like this. I observed this pattern with different OF solvers: simpleF, turbF, dieselF, etc. E.g. -When running a job with 4 processes on a Quadcore machine, the load it higher than 4 (~5). -Even on dual cores load is typically higher ~2.7 (all AMD Opteron machines & used exclusively for OF) When I use a different (master) node to start a run, then slave nodes have "normal loads = num of Proc". To avoid this overloading issue, I am using one CPU for mpirun (i.e. Running with #CPU-1 --- 3 proc on quadcore) It seems that mpirun is responsible for this extra load. Does this mean that OF is not using the CPUs in optimum manner? My guess: when load is more than 100% it is not optimum. Any comments? Rishi |
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May 27, 2009, 18:30 |
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#2 |
Senior Member
Anton Kidess
Join Date: May 2009
Location: Germany
Posts: 1,377
Rep Power: 30 |
A load average slightly higher than one is not necessary very bad. I think a better metric is CPU time vs. walltime. If walltime is not roughly equal to (CPU time / NCPUs), then your parallelization is not very good.
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