[svn-r5680] Purpose:

    New feature.

Description:
    There is some discussion among the SAF team as to whether it is better
    to use MPI derived types for raw data transfers (thus needing a
    MPI_File_set_view() call), or whether it is better to use a sequence of
    low-level MPI types (i.e. MPI_BYTE) for the raw data transfer.

Solution:
    Added an in internal flag to determine whether derived types are preferred
    (the default), or whether they should be avoided.  An environment variable
    ("HDF5_MPI_PREFER_DERIVED_TYPES") can be set by users to control whether MPI
    types should be used or not.  Set the environment variable to "0" (i.e.:
    'setenv HDF5_MPI_PREFER_DERIVED_TYPES 0' to avoid using MPI derived types.

Platforms tested:
    IRIX64 6.5 (modi4) w/parallel

1 files changed, 11 insertions, 5 deletions

diff --git a/src/H5S.c b/src/H5S.c
index 8297909..1b88e5a 100644
--- a/src/H5S.c
+++ b/src/H5S.c
@@ -41,8 +41,9 @@ static size_t			H5S_aconv_g = 0;	/*entries allocated*/
 static size_t			H5S_nconv_g = 0;	/*entries used*/
 
 #ifdef H5_HAVE_PARALLEL
-/* Global var whose value can be set from environment variable also */
-hbool_t         H5_mpi_opt_types_g = TRUE;
+/* Global vars whose value can be set from environment variable also */
+hbool_t H5S_mpi_opt_types_g = TRUE;
+hbool_t H5S_mpi_prefer_derived_types_g = TRUE;
 #endif /* H5_HAVE_PARALLEL */
 
 /* Declare a free list to manage the H5S_simple_t struct */
@@ -94,9 +95,14 @@ H5S_init_interface(void)
     {
         /* Allow MPI buf-and-file-type optimizations? */
         const char *s = HDgetenv ("HDF5_MPI_OPT_TYPES");
-        if (s && HDisdigit(*s)) {
-            H5_mpi_opt_types_g = (int)HDstrtol (s, NULL, 0);
-        }
+        if (s && HDisdigit(*s))
+            H5S_mpi_opt_types_g = (int)HDstrtol (s, NULL, 0);
+    }
+    {
+        /* Prefer MPI derived types for collective data transfers? */
+        const char *s = HDgetenv ("HDF5_MPI_PREFER_DERIVED_TYPES");
+        if (s && HDisdigit(*s))
+            H5S_mpi_prefer_derived_types_g = (int)HDstrtol (s, NULL, 0);
     }
 #endif /* H5_HAVE_PARALLEL */