[Q-e-developers] introduce a parallel communicator derived data type ?

[stefano de gironcoli]

Dear All,

   I would like to in introduce a Parallel Communicator derived data type.

   The aim would be to make the information associated to the different 
parallelization levels more structured and uniform. They already look 
all the same (see intra_image_comm/inter_image_comm, 
intra_pool_comm/inter_pool_comm, intra_bgrp_comm/inter_bgrp_comm,...) 
but this is obtained by quite bit of code duplication and if a 
new/different parallelization level is desired one needs to write more 
almost identical code and double check in many places.

   The parallel communicator data type would allow, in future, to pass 
the communicator as argument of the routines so making the 
parallelization level easily 'local' to the routine that would help 
disentangling the different parallelization levels and possibly 
introduce them when needed rather than all at the beginning.

   I don't know how much this will be possible/desirable but with the 
current structure it is clearly impossible.

   Anyhow, since this is going to have an impact on the distribution at 
all levels I would like to have a preliminary feedback.

   In particular if you see compelling reasons NOT to take such a path !

   best,

stefano


PS: the derived data type would look something like this

TYPE pcomm_type
      CHARACTER(len=35) :: label         ! the name of this 
parallelization level
      INTEGER :: parent_comm = 0         ! the parent communicator from 
which it originates
      INTEGER :: intra_comm = 0          ! intra group communicator
      INTEGER :: inter_comm = 0          ! inter group communicator
      INTEGER :: ngroups = 1             ! number of created groups
      INTEGER :: nproc = 1               ! number of processors per group
      INTEGER :: parent_nproc = 1        ! number of processors of the 
parent communicator
      INTEGER :: my_group_id = 0         ! which of the created groups 
this proc belongs to
      INTEGER :: mype = 0                ! the index (rank) of the 
processor inside its group
      INTEGER :: mype_in_parent_comm = 0 ! should be clear by the name
      INTEGER :: root_group_id  = 0      ! the group_id of the root 
group (it's always 0 as root is the first by def)
      INTEGER :: root = 0                ! the index (rank) of the root 
processor inside the group (it's always 0)
   END TYPE pcomm_type