Hello, I am working on a parallel CFD solver with MPI and I am using an account on a cluster to run my executable. The hardware structure of my account is as follows; Architecture: x86_64 CPU op-mode(s): 32-bit, 64-bit Byte Order: Little Endian CPU(s): 32 On-line CPU(s) list: 0-31 Thread(s) per core: 2 Core(s) per socket: 8 CPU socket(s): 2 NUMA node(s): 2 Vendor ID: GenuineIntel CPU family: 6 Model: 62 Stepping: 4 CPU MHz: 2600.079 BogoMIPS: 5199.25 Virtualization: VT-x L1d cache: 32K L1i cache: 32K L2 cache: 256K L3 cache: 20480K NUMA node0 CPU(s): 0,2,4,6,8,10,12,14,16,18,20,22,24,26,28,30 NUMA node1 CPU(s): 1,3,5,7,9,11,13,15,17,19,21,23,25,27,29,31 Initially, I was running my executable with any binding options and in that case, whenever I was switching from 2 to 4 processors my computation time was also increasing along with communication time inside some iterative loop. Today, somewhere I read about binding options in MPI through which I can manage the allocation of processors. Initially, I used the "-bind-to core" option and the results were different and I got time reduction up to 16 processors and after that with 24 and 32 processors, it has started increasing. Results of timing are as follows; 2 procs- 160 seconds, 4 procs- 84 seconds, 8 procs- 45 seconds, 16 procs- 28 seconds, 24 procs- 38 seconds, 32 procs- 34 seconds. After that, I used some other combinations of binding option but did not get better timing results compared to -bind-to core option. So, I back edited the bind to option to core but now I am getting different timing results with the same executable which are as follows, 2 procs- 164 seconds, 4 procs- 85 seconds, 8 procs- 45 seconds, 16 procs- 48 seconds, 24 procs- 52 seconds, 32 seconds- 98 seconds. I have following two questions for which I am seeking your help, 1. Can anyone please suggest me is it possible an optimum binding and mapping options based on my cluster account hardware topology?? If yes then please tell me. 2. Why I am getting such an irregular pattern of jump in timing without binding option and why with a binding option, my timings are varying for each run? Is it my cluster network problem or my MPI code problem? If you need further details about my iterative loop then please tell me. As this message got too long I can share it later if you think above data is not sufficient. Thank you.