[mpich-discuss] Understanding process bindings in MPICH

[Benson Muite]

On Fri, May 15, 2020, at 8:52 PM, hritikesh semwal via discuss wrote:
> 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.

Hitesh,

You might find the following online workshop useful:
http://www.hlrs.de/training/2020-05-25-VI-HPS/

Regards,
Benson
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