[Beowulf] multi-threading vs. MPI

Douglas Eadline deadline at eadline.org
Mon Dec 10 14:52:25 EST 2007


Some people had asked for more details:

NAS suite version 3.2.1
Test class was: B
Units are Mops (Million operations per second)
see the NAS docs for more information

--
Doug


> 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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--
Doug
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