Hi All, I have 4-Nodes ( 4 CPUs Xeon3085, total 8 cores) Beowulf cluster on ROCKS-5 with GiG-Ethernet. I tested runs of a 1D CFD code both serial and parallel on it. Please reply following:
1) When I run my serial code on the dual-core head node (or parallel code with -np 1); it gives results in about 2 minutes. What I observe is that "System Monitor" application show that some times CPU1 become busy 80+% and CPU2 around 10% busy. After some time CPU1 gets share around 10% busy while the CPU2 becomes 80+% busy. Such fluctuations/swap-of-busy-ness continue till end. Why this is so? Does this busy-ness shifts/swaping harms performance/speed? 2) When I run my parallel code with -np 2 on the dual-core headnode only; it gives results in about 1 minute. What I observe is that "System Monitor" application show that all the time CPU1 and CPU2 remain busy 100%. 3) When I run my parallel code with "-np 4" and "-np 8" on the dual-core headnode only; it gives results in about 2 and 3.20 minutes respectively. What I observe is that "System Monitor" application show that all the time CPU1 and CPU2 remain busy 100%. 4) When I run my parallel code with "-np 4" and "-np 8" on the 4-node (8 cores) cluster; it gives results in about 9 (NINE) and 12 minutes. What I observe is that "System Monitor" application show CPU usage fluctuations somewhat as in point number 1 above (CPU1 remains dominant busy most of the time), in case of -np 4. Does this means that an MPI-process is shifting to different cores/cpus/nodes? Does these shiftings harm performance/speed? 5) Why "-np 4" and "-np 8" on cluster is taking too much time as compare to -np 2 on the headnode? Obviously its due to communication overhead! but how to get better performance--lesser run time? My code is not too complicated only 2 values are sent and 2 values are received by each process after each stage. Regards, Amjad Ali.
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