Open MPI logo

Open MPI User's Mailing List Archives

  |   Home   |   Support   |   FAQ   |   all Open MPI User's mailing list

Subject: Re: [OMPI users] Simple Question regarding MPI Scatterv
From: Hamid Saeed (e.hamidsaeed_at_[hidden])
Date: 2014-04-08 09:12:52


Can someone kindly reply?

On Tue, Apr 8, 2014 at 1:01 PM, Hamid Saeed <e.hamidsaeed_at_[hidden]> wrote:

> 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
>
>

-- 
_______________________________________________
Hamid Saeed
CoSynth GmbH & Co. KG
Escherweg 2 - 26121 Oldenburg - Germany
Tel +49 441 9722 738 | Fax -278
http://www.cosynth.com
_______________________________________________