Re: [OMPI users] MPI_SCAN

[Rohan Deshpande]

Hi jeffy,

Thanks for your reply.

I am not understanding how MPI_Reduce would be useful.

Say I have 3 processes and each process has array [1,2,3,4]

When each process calculates the prefix sum using cuda each process will
have array as [1,3,6,10]

so if I use MPI_Reduce to gather results it returns me sum as 30.

but the original array is [1,2,3,4,1,2,3,4,1,2,3,4] and the prefix sum of
this array should be

[1,3,6,10,11,13,16,20,21,23,26,30]

Is my understanding wrong somewhere?

On Fri, May 18, 2012 at 7:05 AM, Jeff Squyres  wrote:

> You probably want MPI_Reduce, instead.
>
>http://www.open-mpi.org/doc/v1.6/man3/MPI_Reduce.3.php
>
>
> On May 15, 2012, at 11:27 PM, Rohan Deshpande wrote:
>
> > I am performing Prefix scan operation on cluster
> >
> > I have 3 MPI tasks and master task is responsible for distributing the
> data
> >
> > Now, each task calculates sum of its own part of array using GPUs and
> returns the results to master task.
> >
> > Master task also calculates its own part of array using GPU.
> >
> > When each task returns its result (which would be array) master task
> needs to combine all the results to get the final result.
> >
> > Can I use MPI_SCAN to combine the results?
> >
> >
> >
> >
> >
> > ___
> > users mailing list
> > us...@open-mpi.org
> > http://www.open-mpi.org/mailman/listinfo.cgi/users
>
>
> --
> Jeff Squyres
> jsquy...@cisco.com
> For corporate legal information go to:
> http://www.cisco.com/web/about/doing_business/legal/cri/
>
>
> ___
> users mailing list
> us...@open-mpi.org
> http://www.open-mpi.org/mailman/listinfo.cgi/users
>



-- 

Best Regards,

ROHAN DESHPANDE

Re: [OMPI users] MPI_SCAN

[Jeff Squyres]

You probably want MPI_Reduce, instead.

http://www.open-mpi.org/doc/v1.6/man3/MPI_Reduce.3.php


On May 15, 2012, at 11:27 PM, Rohan Deshpande wrote:

> I am performing Prefix scan operation on cluster
> 
> I have 3 MPI tasks and master task is responsible for distributing the data
> 
> Now, each task calculates sum of its own part of array using GPUs and returns 
> the results to master task. 
> 
> Master task also calculates its own part of array using GPU. 
> 
> When each task returns its result (which would be array) master task needs to 
> combine all the results to get the final result.
> 
> Can I use MPI_SCAN to combine the results?
> 
>  
> 
> 
> 
> ___
> users mailing list
> us...@open-mpi.org
> http://www.open-mpi.org/mailman/listinfo.cgi/users


-- 
Jeff Squyres
jsquy...@cisco.com
For corporate legal information go to: 
http://www.cisco.com/web/about/doing_business/legal/cri/

[OMPI users] MPI_SCAN

[Rohan Deshpande]

I am performing Prefix scan operation on cluster

I have 3 MPI tasks and master task is responsible for distributing the data

Now, each task calculates sum of its own part of array using GPUs and
returns the results to master task.

Master task also calculates its own part of array using GPU.

When each task returns its result (which would be array) master task needs
to combine all the results to get the final result.

Can I use MPI_SCAN to combine the results?