[DFTB-Plus-User] DFTB+ maximum number of threads

Ben Hourahine benjamin.hourahine at strath.ac.uk
Tue Mar 15 08:56:43 CET 2016

Hello Anton,

As Bálint says, MKL is probably the limiting factor. Are these 12 cores
or 6 physical cores with hyperthreading (i7 processor)? MKL uses the
physical core count, as there is no advantage for dense operations in
threads sharing a core:

If you really want to enforce a thread count of 12 you might also want
to try the MPI parallel version.



On 15/03/16 07:14, Bálint Aradi wrote:
> Dear Anton,
>> used by program can be successfully controlled by OMP_NUM_THREADS
>> environment variable from 1 to 6, so OpenMP seems to work fine. However,
>> if I try to use more (ideally I would like to use all 12 threads to
>> speed up calculations, I'm trying to work on pretty large cell), it
>> never does. So, the question is, if there are hard coded limits on the
>> maximum number of threads the code can use, or there is some trick to
>> compilation process to make it use more than 6 threads?
> We do not impose any hard coded limit on the number of threads.
> Actually, most threaded activity happens within MKL itself, so it is
> MKL, which apparently refuses to use more threads. But the question is
> really, does your machine recognise 6 or 12 threads? Usually MKL
> launches as many threads, as the OS reports cores on the machine.
>   Best regards,
>   Bálint
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