[mpich-discuss] my mpi code goes slow after some time

[Lu, Huiwei]

(Please don’t drop the discussion thread, added it back.)

Is 1.0 second for one step or for the whole application time?

Also, can you provide the following information of your program?
1. What’s the version of your MPI? 
2. How many processes you use?
3. Can you give us a minimum working example of your code so that we can reproduce your problem?

You can read a tutorial of parallel computing here: https://computing.llnl.gov/tutorials/parallel_comp/
—
Huiwei

On Apr 14, 2014, at 10:54 AM, harsh soni <harshiisc at gmail.com> wrote:

> Dear Huiwei,
> 
> Thanks for the replay. I tried to calculate the time taken by the various segments in my code. I realize, the slowest part correspond to hug communication between cores, with  communication of  15750 double precision pre core, at every step. The time taken by this communication is around 1.0 second. I just want to know, how the communication affects the speed of code. I read about "parallel slowdown". Can please tell me something about it. 
> 
> Sorry for bothering you! 
> 
> Thanks
> Harsh Soni
> Ph.D. student,
> IISc, Bengaluru (India)
> 
> 
> 
> On Thu, Apr 10, 2014 at 6:47 PM, Lu, Huiwei <huiweilu at mcs.anl.gov> wrote:
> How slow is that? What’s the version of your MPI? How many processes you use?
> 
> If only 0.3% RAM was used for each core, it was unlikely the code went slow because of running out of RAM. Can you give us a minimum working example of your code so that we can reproduce your problem?
> 
> —
> Huiwei Lu
> Postdoc Appointee
> Mathematics and Computer Science Division, Argonne National Laboratory
> http://www.mcs.anl.gov/~huiweilu/
> 
> On Apr 10, 2014, at 7:57 AM, harsh soni <harshiisc at gmail.com> wrote:
> 
> > Hi,
> > I am running a mpi code on cluster. It goes slow after some time. I don't allocate any array in main for loop, every array is allocated initially. Each core is showing  0.3 to 0.5 % RAM  usage. doe sit go slow due to the RAM. I use fortran language.
> >
> >
> > Thanks
> >
> > With best regards
> > Harsh Soni
> > Ph.D. student,
> > IISc, Bengaluru (India)
> >
> >
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