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Subject: Re: [OMPI users] Simple Question regarding MPI Scatterv
From: Hamid Saeed (e.hamidsaeed_at_[hidden])
Date: 2014-04-08 11:05:02


Yes i meant Parallel file system.

And can you kindly explain what exactly happens if
the RANK0 want to send to RANK0?

Why does MPIO is different in time consumption than RANK0 to RANK0
communication?

On Tue, Apr 8, 2014 at 4:45 PM, Ralph Castain <rhc_at_[hidden]> wrote:

> I suspect it all depends on when you start the clock. If the data is
> sitting in the file at time=0, then the file I/O method will likely be
> faster as every proc just reads its data in parallel - no comm required as
> it is all handled by the parallel file system.
>
> I confess I don't quite understand your reference to "shared memory" in
> the MPIO case, but I suspect what you really meant was just "parallel file
> system"?
>
>
> On Apr 8, 2014, at 6:12 AM, Hamid Saeed <e.hamidsaeed_at_[hidden]> wrote:
>
> 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
> _______________________________________________
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>
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-- 
_______________________________________________
Hamid Saeed
CoSynth GmbH & Co. KG
Escherweg 2 - 26121 Oldenburg - Germany
Tel +49 441 9722 738 | Fax -278
http://www.cosynth.com
_______________________________________________