[mpich-discuss] mpich runs

[Gus Correa]

Hi Luis, Reuti, Rajeev, list

I wonder if the different wall times really indicate an error.

Cpi.c uses MPI_Wtime(), right?
There was a recent discussion in the OpenMPI list about
how good a measure of time this produces, particularly
in multi-core multi-socket systems.
See this thread:
http://www.open-mpi.org/community/lists/users/2010/10/14456.php

My two cents,
Gus Correa


Luis Del Castillo wrote:
> Everytime I run mpirun -np 5 or -np 8 the results for PI are 
> the same but the wall clock time is different. 
> 
> -----Original Message-----
> From: Reuti [mailto:reuti at staff.uni-marburg.de] 
> Sent: miércoles, 20 de octubre de 2010 08:31 a.m.
> To: mpich-discuss at mcs.anl.gov
> Subject: Re: [mpich-discuss] mpich runs
> 
> Am 20.10.2010 um 00:30 schrieb Luis Del Castillo:
> 
>> Hi fellows my name is Luis Alejandro Del Castillo 
> and am  having issues to figure it out why if run 
> mpirun twice with the same configuration give me 2 different answers.
>>  
>> wrf at cl2master-> ./mpirun -np 5 ../examples/cpi
>> Process 0 on cl2master
>> Process 1 on node1
>> Process 3 on node3
>> Process 4 on node4
>> Process 2 on node2
>> pi is approximately 3.1416009869231245, Error is 0.0000083333333314
>> wall clock time = 0.007812
>> wrf at cl2master-> ./mpirun -np 5 ../examples/cpi
>> Process 0 on cl2master
>> Process 3 on node3
>> Process 1 on node1
>> Process 2 on node2
>> Process 4 on node4
> 
> Do you mean the different order in stdout? AFAIK this cannot be predicted.
> 
> -- Reuti
> 
> 
>> pi is approximately 3.1416009869231245, Error is 0.0000083333333314
>> wall clock time = 0.000000
>> wrf at cl2master->
>>  
>> I have a Quad Core Beowulf cluster with 11 nodes (1 master , 10 slaves) all the same configuration.
>> I want to do this because I am trying to explain the performance doing some graph.
>>  
>> Thanks
>>  
>>  
>> Luis Alejandro Del Castillo Riley
>> luis.delcastillo at cathalac.org
>> Soporte de Tecnología / IT Support  
>> CATHALAC
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