[Wien] pondering wien2kMPI performance

[Robert Laskowski]

Hi,
lapw0 is parallelized in loop over atoms, there is little communication here, 
and fftw, for that look at fftw manual. For lapw1, setup has no communication 
at all, eigensolver is done with pblas and scalapack calls, here both latency 
and bandwidth are important, but these libraries should be well optimized, I 
would point more to bandwidth. lapw2 uses two coexisting communicators, one 
for parallelization vs atoms, and the other for splitting vector 
(lapw2_vector_split  in .machines), for large systems you have to split 
vector. I guess that here major time is used in pblas calls, which are 
matrix/matrix multiplications, however on some old and less efficient systems 
we have notice huge time spend on reading and distributing the vector file. 

regards

Robert
  

On Monday 06 June 2011 23:31:44 Kevin Jorissen wrote:
> Dear wien2k community,
> 
> I have a few basic questions regarding the MPI/SCALAPACK version of wien2k
> :
> 
> * does anyone have a formula for calculating the memory requirements
> of the code (lapw0/1/2) given, say, nmat and nume and the number of
> cores used?  It's easy enough for the serial code, but I'm sometimes
> baffled by the memory taken by each of the MPI threads when
> distributing the job over N cores.  It's sometimes very different from
> [serial size in GB] / N_cores.  It makes the queue manager unhappy,
> and occasionally I unintentionally overload a node this way.
> 
> * I was asked the following question about the MPI wien2k code :
> >> So would it be correct to state that your apps are more bandwidth
> >> sensitive than latency sensitive?
> 
> and I don't know what to answer.  Thinking about LARGE calculations
> (hundreds of atoms) I want to say that both will be important ...
> Does anyone have a more sophisticated insight here?
> 
> 
> 
> cheers,
> 
> 
> Kevin Jorissen
> University of Washington
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-- 
Dr Robert Laskowski
Vienna University of Technology, Institute of Materials Chemistry, 
Getreidemarkt 9/165-TC, A-1060 Vienna, Austria
tel. +43 1 58801 15675               Fax  +43 1 58801 15698