[Beowulf] multi-threading vs. MPI

Renato S. Silva rssr at lncc.br
Mon Dec 10 04:39:41 EST 2007


Hi

What is the CLASS you are using ?

One point is how the OpenMP version leads with memory, in relation to  
MPI version

I have two  sugestions

 I will be a good ideia to try to use the Intel compiler and
Why not download and run the multi-zone NAS benchmarks ?
It can give a complete view of the "problem"

They have :

>    NPB3.2-MZ-SER:  a serial version
>    NPB3.2-MZ-MPI:  a hybrid MPI + OpenMP version
>    NPB3.2-MZ-SMP:  a hybrid SMP + OpenMP version

I run in a very small clusters 4 core 2 duo,  using Intel compilers and 
it seens
and for the CLASS=C  I get this numbers for the MPI version and MPI+ OpenMP
with one (Hibrid(1))and two (Hibrib(2)) threads

>
> N. Processors  -     MPI     -  Hibrid (1)  -  Hibrid (2)
>        1               -  2496.59   -       *           - 1682.07
>        2               -  1085.58   -       *           -  846.82 
>        4               -    624.69   -   674.28      -   498.65
>        8               -    447.7     -   467.79      -   *     
>
Unfortunate they dont have a version with only OpenMP  I and I dont know 
if the results with one MPI process and several threads cam be usefull.

Notice that the benchmarks are different LU version from the NPB2.0
they change the "memory acess" .


Renato


Douglas Eadline wrote:

>I like answering these types of questions with numbers,
>so in my Sept 2007 Linux magazine column (which should
>be showing up on the website soon) I did the following.
>
>Downloaded the latest NAS benchmarks written in both
>OpenMP and MPI. Ran them both on an 8 core Clovertown
>(dual socket) system (multiple times) and reported
>the following results:
>
>Test      OpenMP              MPI
>       gcc/gfortran 4.2    LAM 7.1.2
>------------------------------------
>CG         790.6             739.1
>EP         166.5             162.8
>FT        3535.9            2090.8
>IS          51.1             122.5
>LU        5620.5            5168.8
>MG        1616.0            2046.2
>
>My conclusion, it was a draw of sorts.
>The article was basically looking at the
>lazy assumption that threads (OpenMP) are
>always better than MPI on a SMP  machine.
>
>I'm going to re-run the tests using Harpertowns
>real soon, maybe try other compilers and MPI
>versions. It is easy to do. You can get the code here:
>
>http://www.nas.nasa.gov/Resources/Software/npb.html
>
>--
>Doug
>
>
>
>
>
>
>
>
>
>  
>
>>On this list there is almost unanimous agreement that MPI is the way to go
>>for parallelism and that combining multi-threading (MT) and
>>message-passing
>>(MP) is not even worth it, just sticking to MP is all that is necessary.
>>
>>However, in real-life most are talking and investing in MT while very few
>>are interested in MP. I also just read on the blog of Arch Robison " TBB
>>perhaps gives up a little performance short of optimal so you don't have
>>to
>>write message-passing " (here:
>>http://softwareblogs.intel.com/2007/11/17/supercomputing-07-computer-environment-and-evolution/
>> )
>>
>>How come there is almost unanimous agreement in the beowulf-community
>>while
>>the rest is almost unanimous convinced of the opposite ? Are we just
>>tapping
>>ourselves on the back or is MP not sufficiently dissiminated or ... ?
>>
>>toon
>>
>>
>>
>>_______________________________________________
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>>    
>>
>
>
>--
>Doug
>_______________________________________________
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>
>  
>


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