[CP2K-user] ssmp and CPU loads

[Alex]

Hi all,

We've just built the latest version according to 
https://www.cp2k.org/howto:compile?s[]=ssmp

The main use case is single-node multi-CPU (36 cores /72 threads 
available), so SSMP appeared like the correct option, i.e., none of the run 
commands involving mpirun. Our understanding is that the executable will 
use all available threads. We have confirmed it using a small system (~50 
atoms) -- the system load shows one instance of cp2k with something like 
2400% load, which is similar to for example how Gromacs runs using OpenMP. 
So, all is great.

However, when running a large system containing ~1000 atoms, there is a 
single cp2k instance with 100% load and ~1TB RAM usage. SCF updates are 
sluggish, but it's a large system, so we can't tell if it's due to size or 
the fact that the CPU load is improperly low. Here is my question: is this 
correct behavior? Is there a way or need to force a particular number of 
threads to run on? Are we building the correct version for our needs?

Another, more minor question: does multithreading help CP2K performance? 
The same machine is used for coupled cluster calculations and the users 
insist that HT hurts their performance, so it's currently off. 

Many thanks,

Alex
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