[mpich-discuss] problem with collective on sub-communicator

[Miguel Oliveira]

Hi,

Here is why....

93:master_slave miguel$ mpicc -o master_slave master_slave.c 
93:master_slave miguel$ mpiexec -n 10 ./master_slave

Average=5.478889e+00

93:master_slave miguel$ mpiexec -n 10 ./master_slave

Average=5.563333e+00

93:master_slave miguel$ mpiexec -n 10 ./master_slave

Average=5.384444e+00

93:master_slave miguel$ mpiexec -n 10 ./master_slave

Average=5.565556e+00

93:master_slave miguel$ mpiexec -n 10 ./master_slave
Oops...

This output is generated with the attached code which only differs from the one I sent previously by the if statement that prints the "Oops..." in the deadlock case....

Cheers,

MAO

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On Nov 11, 2011, at 04:16 , Pavan Balaji wrote:

> 
> Even if I remove it, the program just prints a number. What makes you believe that the MPI_Send is overtaking the Reduce?
> 
> -- Pavan
> 
> On 11/10/2011 10:12 PM, Miguel Oliveira wrote:
>> Hi,
>> 
>> Sorry, sent the version with the only correction I found that makes it work. Remove the MPI_Barrier(world) in both the master and the slaves and you should be able to reproduce the problem.
>> 
>> Cheers,
>> 
>> MAO
>> 
>> On Nov 11, 2011, at 03:31 , Pavan Balaji wrote:
>> 
>>> 
>>> The test code you sent seems to work fine for me. I don't see any such problem.
>>> 
>>> -- Pavan
>>> 
>>> On 11/10/2011 03:14 PM, Miguel Oliveira wrote:
>>>> Hi all,
>>>> 
>>>> I wrote a very simple master/slave code in MPI and I'm having problems with MPI_Reduce, or even, MPI_Barrier, inside a subset of the world communicator.
>>>> These operations don't seem to be waiting for all the processes in the subgroup.
>>>> 
>>>> The code is a straightforward master/slave case where the master generates random numbers when requested and then retrieves a reduction of the sum of these
>>>> done on the slaves.
>>>> 
>>>> When run on more than three processes sometimes it happens that the message after the reduction, done from one of the slaves to inform the master of the final
>>>> result gets to the master before some of the requests for random numbers... This ought to be impossible with a blocking reduction...
>>>> 
>>>> Am I missing something?
>>>> 
>>>> Code is attached.
>>>> 
>>>> Help is appreciated.
>>>> 
>>>> Cheers,
>>>> 
>>>> MAO
>>>> 
>>>> 
>>>> 
>>>> 
>>>> _______________________________________________
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>>>> To manage subscription options or unsubscribe:
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>>> 
>>> --
>>> Pavan Balaji
>>> http://www.mcs.anl.gov/~balaji
>> 
> 
> -- 
> Pavan Balaji
> http://www.mcs.anl.gov/~balaji

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