[Pw_forum] The -D__USE_3D_FFT option in PW

[Filippo Spiga]

Dear Paul,

On Jan 22, 2014, at 8:05 PM, Paul.Caheny at uk.fujitsu.com wrote:
> Any other information about the purpose/applicability/trade-offs involved in this option would also be very useful.


It works if you run K-point calculations and each pool has a size of 1 (meaning "-npool N" where N is equal of the number of MPI processes). In this way you can collapse FFT calculations to be totally local within a MPI process. In such a way, z-stick are distributed in a serial fashion and you can call any 3D FFT serial library. More k-point you have, more N can grow. But it is obvious where the limit is.

There are trade-off for sure, I noticed that by reducing communication intra_pool the communication between pools becomes more intensive. I have no numbers to show but I can easily run few tests using QE-GPU.

I am not aware about other special cases.

HTH
F

--
Mr. Filippo SPIGA, M.Sc.
Quantum ESPRESSO Foundation
http://www.linkedin.com/in/filippospiga ~ skype: filippo.spiga

«Nobody will drive us out of Cantor's paradise.» ~ David Hilbert

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