[Wien] speedup with mpi

[pluto]

Dear All,

Does anyone has experience in running WIEN2k on a cluster or 
supercomputer with both k-parallel and mpi? My interest is in band 
structure calculations of large slabs (e.g. >20 atoms). I would 
appreciate any comment/remark.

- I am wondering if there is a realistic speedup when using mpi? Can I 
have e.g. 10x speedup only from mpi, compared to single core? Will 
speedup then multiply with k-parallel?

- Does mpi on a single node also suffer from the memory bandwidth 
(related to the number of memory channels on the chipset/mainboard)?

- Has anyone been able to find a workaround for the passwordless ssh for 
running on a cluster/supercomputer?

- Is the memory bandwidth problem intrinsic to LAPW, or specific to 
WIEN2k? With two memory channels on desktop machines, the k-parallel 
speedup is only up to something like 4 cores (depending on OMP a bit). 
Actually WIEN2k speed does increase quite a lot with the RAM speed (e.g. 
DDR5 7200) -- this is the case on i9-14900 that I am using in the 
office.

For few years I have been using an older slurm cluster, and jobs 
typically crash when using more that 8 or 10 nodes with k-parallel (also 
with small OMP, I think this has been discussed in the mailing list). In 
my case each node has 8 cores and 4 memory channels, so it can do 8 
k-parallel jobs with practically linear speedup. I would say that in 
general extra speedup with OMP is not significant, and the real speedup 
is only with k-parallel (but as motioned it is limited by the effective 
number of nodes, probably because slurm does not like too many 
passwordless ssh connections).

I am asking because I am wondering if an effort to setup WIEN2k on a 
supercomputer makes any sense at all. Having a bit faster single core 
might not be worth the effort.

Best,
Lukasz