From c9f1103728f4f8626f516bb8abad4c516549e68d Mon Sep 17 00:00:00 2001
From: Antoine Cyril David Hoffmann <ahoffman@spcpc606.epfl.ch>
Date: Thu, 15 Apr 2021 11:48:40 +0200
Subject: [PATCH] Avoid calling MPI comm routines if only one proc in p
---
src/collision_mod.F90 | 38 +++++++++++++++++++++++---------------
1 file changed, 23 insertions(+), 15 deletions(-)
diff --git a/src/collision_mod.F90 b/src/collision_mod.F90
index 84e0b947..d84f7a1e 100644
--- a/src/collision_mod.F90
+++ b/src/collision_mod.F90
@@ -239,13 +239,17 @@ CONTAINS
CALL apply_COSOlver_mat_e(ip,ij,ikr,ikz,TColl)
local_sum_e(ip) = TColl
ENDDO
- ! Sum up all the sub collision terms on root 0
- CALL MPI_REDUCE(local_sum_e, buffer_e, pmaxe+1, MPI_DOUBLE_COMPLEX, MPI_SUM, 0, comm_p, ierr)
-
- ! distribute the sum over the process among p
- CALL MPI_SCATTERV(buffer_e, counts_np_e, displs_np_e, MPI_DOUBLE_COMPLEX,&
- TColl_distr_e, local_np_e, MPI_DOUBLE_COMPLEX,&
- 0, comm_p, ierr)
+ IF (num_procs_p .GT. 1) THEN
+ ! Sum up all the sub collision terms on root 0
+ CALL MPI_REDUCE(local_sum_e, buffer_e, pmaxe+1, MPI_DOUBLE_COMPLEX, MPI_SUM, 0, comm_p, ierr)
+ ! distribute the sum over the process among p
+ CALL MPI_SCATTERV(buffer_e, counts_np_e, displs_np_e, MPI_DOUBLE_COMPLEX,&
+ TColl_distr_e, local_np_e, MPI_DOUBLE_COMPLEX,&
+ 0, comm_p, ierr)
+ ELSE
+ TColl_distr_e = local_sum_e
+ ENDIF
+ ! Write in output variable
DO ip = ips_e,ipe_e
TColl_e(ip,ij,ikr,ikz) = TColl_distr_e(ip)
ENDDO
@@ -256,14 +260,18 @@ CONTAINS
CALL apply_COSOlver_mat_i(ip,ij,ikr,ikz,TColl)
local_sum_i(ip) = TColl
ENDDO
- ! Reduce the local_sums to root = 0
- CALL MPI_REDUCE(local_sum_i, buffer_i, pmaxi+1, MPI_DOUBLE_COMPLEX, MPI_SUM, 0, comm_p, ierr)
-
- ! buffer_e contains the entire collision term along p, scatter it among
- ! the other processes (use of scatterv since Pmax/Np is not an integer)
- CALL MPI_SCATTERV(buffer_i, counts_np_i, displs_np_i, MPI_DOUBLE_COMPLEX,&
- TColl_distr_i, local_np_i, MPI_DOUBLE_COMPLEX, &
- 0, comm_p, ierr)
+ IF (num_procs_p .GT. 1) THEN
+ ! Reduce the local_sums to root = 0
+ CALL MPI_REDUCE(local_sum_i, buffer_i, pmaxi+1, MPI_DOUBLE_COMPLEX, MPI_SUM, 0, comm_p, ierr)
+ ! buffer contains the entire collision term along p, we scatter it between
+ ! the other processes (use of scatterv since Pmax/Np is not an integer)
+ CALL MPI_SCATTERV(buffer_i, counts_np_i, displs_np_i, MPI_DOUBLE_COMPLEX,&
+ TColl_distr_i, local_np_i, MPI_DOUBLE_COMPLEX, &
+ 0, comm_p, ierr)
+ ELSE
+ TColl_distr_i = local_sum_i
+ ENDIF
+ ! Write in output variable
DO ip = ips_i,ipe_i
TColl_i(ip,ij,ikr,ikz) = TColl_distr_i(ip)
ENDDO
--
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