[Wien] MPI Strategy

[Peter Blaha]

Please read the doku about parallelization in the WIEN2k usersguide.
mpi-parallelization is NOT done over k-points.

mpi-parallelization is useful ONLY for bigger cases, where "big" depends
on your machine, accuracy and number of processes you want to use.
Typically, the "blocksize" of an mpi-block should still be at least 1500x1500,
better a bit larger.
If your matrix size is 10000, you may use up to 6x6=36 (or 6x4=24 in your case) cores, which gives you
10000/6 as "blocksize". Probably scaling becomes already problematic ...

If your matrix size is smaller/bigger, you have to adjust the number of cores which are
useful. Eventually, mpi-parallelization is NOT useful at all.


When you say: "This machine does not allow passwordless ssh"

what exactly do you mean by that ??

I guess you have to use a queuing system ?? Which one ??
Could it be, that ssh is blocked interactively, but it works fine within a
batch-job ?
Sometimes, rsh works within batch-jobs,...
You need to have some doku or some expert on the specific machine.
I'm pretty confident that there are rather simple ways to overcome any
restrictions due to a special sysadmin-setup, but most one needs to
know all kinds of details and testing ...

Am 01.04.2011 14:05, schrieb David Tompsett:
> Dear All,
>
> I have recently moved my Wien2k calculations to a new machine (Hector in the UK). This machine does not allow passwordless ssh and therefore disables the k-point parallel part of
> Wien2k. I therefore want to clarify some points about how MPI (chiefly lapw1_mpi) works in Wien2k.
>
> If I run a calculation with say 5 k-points using 5 nodes that each have 24 cores, then will the MPI call of lapw1_mpi split the 5 k-points over the 5 nodes? Or will it simply run
> the k-points one at a time, using all 120 cores for each one?
>
> Is there any documentation I can read about the MPI parallel strategy more generally?
>
> Many thanks,
> David Tompsett.
>
>
>
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                                       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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