[Q-e-developers] QE-GPU and QE trunk, one step toward convergency

[Filippo Spiga]

Dear developers,

due to on-going internal restructuring it is very difficult for me to keep constantly aligned the plugin to the latest version of the trunk. Despite I tried to put in place a set of naive scripts (not perfect scripts, just something semi-automatic to help me figure out which changes in the trunk may impact on the GPU code), I have to manually look very often to the code and fix dependencies. Until now, my philosophy was to completely let the trunk completely ignore the existence of the QE-GPU plugin. However it is not practical from a development point of view, not anymore. 

What I would like to do, is to let the code in the trunk (so the main code) call eventually GPU routines if the plugin is used. This can be easily achieved by isolate piece of code with a preprocessor macro (__CUDA). 

Here an example of the changes I have in mind applied to "PW/scr/addusdens.f90"):

!----------------------------------------------------------------------
SUBROUTINE addusdens(rho)
  !----------------------------------------------------------------------
  !
  USE realus,               ONLY : addusdens_r
  USE control_flags,        ONLY : tqr
  USE noncollin_module,     ONLY : nspin_mag
  USE fft_base,             ONLY : dfftp
  USE kinds,                ONLY : DP
  !
  IMPLICIT NONE
  !
  !
  REAL(kind=dp), intent(inout) :: rho(dfftp%nnr,nspin_mag)
  !
  IF ( tqr ) THEN
     CALL addusdens_r(rho,.true.)
  ELSE
#if defined(__CUDA)
     CALL addusdens_g_gpu(rho)
#else
     CALL addusdens_g(rho)
#endif
  END IF
  !
  RETURN
  !
END SUBROUTINE addusdens


The routine "addusdens_r_gpu" will be in a separate file called for example "addusdens_gpu.f90" under the GPU directory. This file will be compiled iff the proper Makefile.gpu (generated by "GPU/install/configure") is used. From a generic non-GPU user perspective, any piece of code or routine encapsulated by __CUDA will be ignored. Simple but very effective.

I understand that introducing in several parts of the trunk the macro __CUDA may look a dirty move but this will save a lot of my time and it will simplify my job. Plus it might stimulate new people to develop code for QE-GPU.

Paolo, Layla… any opinion?

If I can do that, I expect to commit all the changes by mid of this week.

Cheers,
Filippo

--
Mr. Filippo SPIGA, M.Sc.
http://filippospiga.me ~ skype: filippo.spiga

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

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