Dear Profs. Blaha, Marks,
Thank you for the information!
Could you give an estimate what could be a possible speed-up when I use
mpi parallelization?
My tests on 36-inequivalent-atom slab so far indicate that there is
nearly no difference between different k-parallel and OMP settings. So
far I tried
8x 1:localhost with OMP=2
16x 1:localhost with OMP=1
16x 1:localhost with OMP=2 (means slight overloading)
and the time per SCF cycle (runsp without so) is practically the same in
all these. Later I will also try higher OMP with less 1:localhost, but I
doubt this can possibly be faster.
I have i7-13700K with 64 GB of RAM and NVMe SSD. During 36-atom-slab
parallel calculation around 35 GB is used.
Best,
Lukasz
PS: Now omp_lapwso also works for me in .machines. I think it was a SOC
issue with my test case (which was bulk Au). I am sorry for this
confusion.
On 2023-02-14 10:23, Peter Blaha wrote:
I have no experience for such a CPU with fast and slow cores.
Simply test it out how you get the fastest turnaround for a fixed
number of k-points and different number of processes (should be
compatible with your k-points) and OMP=1-2 (4).
Previously, overloading (using more cores than the physical cores) was
NOT a good idea, but I don't know how this "fused" CPU behaves. Maybe
some "small" overloading is ok. This all depends on #-kpoints and
available cores.
PS:
I cannot verify your omp_lapwso:2 failure. My tests run fine and the
omp-setting is taken over properly.
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
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