Request suggestions for cray xe6

[carlo antonio pignedoli]

Dear all,
I have the impression I am missing many recent improvements of the code,
I was not able to follow them.

I usually run standard DFT calculations for bulk/surface systems with
700-1500 atoms (10 to 18 electrons each)
on a Cray Xe6 (AMD Interlagos 2 x 16-core 64-bit CPUs, 32 GB per compute node)

Do you have suggestions for parameters that would allow for an optimal use of
this architecture? (a problem I have is the limited amount of memory
per core 1GB)

Thanks in advance for your help

Carlo

[Axel]

you should compile with OpenMP support (which also means,

that you have to ditch the crappy default PGI programming environment

and use gcc/gfortran instead).

for plain quickstep calculations there should be a

significant performance increase when running with

4 MPI tasks per node and 8 threads per MPI task.

due to the massively reduced need for data

replication, you should not run out of memory.

since interlagos CPUs do some kind of improved

hyperthreading and two tasks will have to share

a floating point unit, i would expect that you should

get a large improvement already by just using

only half the cores when using plain MPI only.

make sure that you use the proper "distance"

flag to aprun, however, since you need to make

sure you have exactly one MPI task per 

"bulldozer" subunit.

i would talk to the user support specialists

of the machine, to make sure you get it right.

cheers,

    axel.

[carlo antonio pignedoli]

Thanks a lot Axel,
I successfully compiled the OpenMP version with gfortran,
I will countercheck with the specialists that I am doing everything right
with the aprun flags

Ciao

Carlo

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