[Wien] Parallel execution on new Intel CPUs

[pluto]

Dear All,

I am now using a machine with i7-13700K. This CPU has 8 performance 
cores (P-cores) and 8 efficient cores (E-cores). In addition each P-core 
has 2 threads, so there is 24 threads alltogether. It is hard to find 
some reasonable info online, but probably a P-core is approx. 2x faster 
than an E-core:
https://www.anandtech.com/show/17047/the-intel-12th-gen-core-i912900k-review-hybrid-performance-brings-hybrid-complexity/10
This will of course depend on what is being calculated...

Do you have suggestions on how to optimize the .machines file for the 
parallel execution of an scf cycle?

On my machine using OMP_NUM_THREADS leads to oscillations of the CPU use 
(for a large slab maybe 40% of time is spent on a single thread), 
suggesting that large OMP is not the optimal strategy.

Some examples of strategies:

One strategy would be to repeat the line
1:localhost
24 times, to have all the threads busy, and set OMP_NUM_THREADS=1.

Another would be set the line
1:localhost
8 times and set OMP_NUM_THREADS=2, this would mean using all 16 physical 
cores.

Or perhaps one should better "overload" the CPU e.g. by doing 
1:localhost 16 times and OMP=2 ?

Over time I will try to benchmark some the different options, but 
perhaps there is some logic of how one should think about this.

In addition I have a comment on .machines file. It seems that for the 
FM+SOC (runsp -so) calculations the

omp_global

setting in .machines is ignored. The

omp_lapw1
omp_lapw2

settings seem to work fine. So, I tried to set OMP for lapwso 
separately, by including the line like:

omp_lapwso:2

but this gives an error when executing parallel scf.

Best,
Lukasz