[mpich-discuss] High school project on distributed computing

[Guo, Yanfei]

Hi Alex,


On 5/18/16, 6:26 PM, "Alexandre Vieira" <nullpt at gmail.com> wrote:

>Hello list,
>
>
>I'm currently writing a paper on distributed computing and also elaborate a simple use case to include as a proof of concept.
>
>
>My setup:
>
>
>- 3 VMs running on different machines (same HW) with 1 CPU and 2GB RAM running FreeBSD 10.3
>- Connected through a 1Gbps LAN and communicate passwordless through SSH.
>
>- MPICH 3.2_1 installed and working on the three nodes
>
>
>I've tried to compile and run some code samples that are available for mpich (i.e:
>http://people.sc.fsu.edu/~jburkardt/c_src/mpi/search_mpi.c)  but I always end up getting worst times running on the 3 nodes that I get running on 1 node alone, even when I can get all
> 3 nodes to get up to a 100% CPU usage for a couple of minutes.
>
How much slower? When you say running on 1 node, do you mean all three VMs are on the same physical machine, or just running a serial implementation of the program? How many CPU cores does the physical machine have?
>
>I know there is network overhead and SSH isn't helping either, so without investing too much time I unfortunately won't have, I'd like to ask you what kind of simple program could I write just for the sake of a proof of concept
> that running a program with 3 nodes would be faster than running on one.
>
Network latency could be a problem because the communication goes through memory when all processes/VMs are on the same physical machine, which is way faster then Ethernet.
>
>Maybe dealing with slower operations like disk I/O do counter the inter-node communication?
>
It is unlikely that disk I/O has something to do with this.
>
>Many thanks for your kind help
>
>
>BR
>Alex
>
>

Yanfei Guo
Postdoctoral Researcher
MCS Division, ANL


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