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Subject: Re: [OMPI users] Simple Question regarding MPI Scatterv
From: Hamid Saeed (e.hamidsaeed_at_[hidden])
Date: 2014-04-08 07:01:36


Hello,

I think that the MPI open its sockets even though the number of processor
is only 1 on the same machine?
regards.

On Tue, Apr 8, 2014 at 9:43 AM, Hamid Saeed <e.hamidsaeed_at_[hidden]> wrote:

> Hello all,
>
> I have a very basic question regarding MPI communication.
>
> In my Task, what i am doing is..
> Comparing Scatterv and MPIO.
> 1) In scatterv, I scatter all the data to the other ranks and SCAN for the
> specific characters.
> MPI_Scatterv (chunk, send_counts, displacements, MPI_CHAR, copychunk, smallchunk_size,
> MPI_CHAR, 0, MPI_COMM_WORLD);
> &
> 2) On the other hand using MPIO, I have the data available in the shared
> memory and every rank searches in the specific chunk.
> MPI_File_open(MPI_COMM_WORLD, "170mb.txt", MPI_MODE_RDONLY, MPI_INFO_NULL,
> &in);
> here i assign every processor to search in a specific "chunk"
>
>
> My question is..
>
> Why MPI_Scatterv using 1 processor takes more time then MPI_File_open?
> How does MPI sending and receiving takes place?
>
> I think using 1 processor does not include physical sending and
> receiving. Then why it consumes more clock?
>
> In the attachment you can observe the plots in which i performed some
> tests using both algorithms.
>
> Kindly explain briefly the mpi communication using 1 processor and
> multiple processors.
>
>
> Thanks in advance.
>
> Regards
> Hamid
>

--
Hamid