[Wien] k point parallel in a supercomputer that returns a single name for .machines file

[Peter Blaha]

> Yes, I have 14 k-points and would like to run k-parallel job and not
> MPI parallel jobs for 14 PE.
> This seems to be not possible in an efficient way for wien2k in
> machines which have nodes of 2-12 cores.
> Did I get this right?
> If so I'd add k-point only parallelism for multicore setups to my wish
> list, or is there some reason why this would not make sense?

No, you did not get this right. Wien2k is very well suited for k-point
parallelization for multicore setups.
In fact, k-point parallelization is always preferred over mpi-parallelization,
unless the systems become so big, that they cannot run on one core.

In my previous email I only tried to explain, how you could "optimize" the performance
on some "bad" and unbalanced systems.
(A "bad" system is running a single program X in 100 sec, but when running
this program N times simultaneously (N...number of cores) it takes 150 or more seconds,
while on a "good" system the increase of cpu-time is smaller (10-20 percent).

But with either kind of parallelization YOU must tell which nodes one should
use for parallelization.

PS: was the test on login6 a 12 core machine ?
Your machines file will create 12 parallel jobs with one k-point and once they finish,
2 more jobs with 1 k-point will be scheduled (assuming you have 14 k-points) , while the
other cores will idle.
Thus in this case I'd use 7 lines, so that only 7 parallel jobs with 2 k-points each are
started. (In addition you may specify OMP_NUM_THREAD)

Computing is an "art", but there is no way out if you want to use a machine efficiently.

>
>>
>> Now you have to find out in your job script, which nodes you got.
>> I'd assume,     echo $PBS_NODEFILE
>> gives you the required info. On the PBS I've used, it would give me a list
>> of 14 names.
> This seems to be my problem in this particular system. For some reason
> $PBS_NODEFILE gives me only one name eventhough
> there should be at least two node names in this case. I try to sort this out.
>
> Merry Christmas from the land of Santa,
> Markus
>

-- 

                                       P.Blaha
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-15671             FAX: +43-1-58801-15698
Email: blaha at theochem.tuwien.ac.at    WWW: http://info.tuwien.ac.at/theochem/
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