coll/libnbc: optimize size one communicators

simply "return" with ompi_request_empty if the communicator size is 1

Signed-off-by: Gilles Gouaillardet <gilles@rist.or.jp>

ompi/mca/coll/libnbc/nbc_iallgather.c

@@ -5,7 +5,7 @@
  *                         Corporation.  All rights reserved.
  * Copyright (c) 2006      The Technical University of Chemnitz. All
  *                         rights reserved.
- * Copyright (c) 2014-2016 Research Organization for Information Science
+ * Copyright (c) 2014-2017 Research Organization for Information Science
  *                         and Technology (RIST). All rights reserved.
  * Copyright (c) 2015      Los Alamos National Security, LLC.  All rights
  *                         reserved.
@@ -74,6 +74,10 @@ int ompi_coll_libnbc_iallgather(const void* sendbuf, int sendcount, MPI_Datatype
       return res;
     }
   }
+  if (1 == p) {
+    *request = &ompi_request_empty;
+    return OMPI_SUCCESS;
+  }
 
 #ifdef NBC_CACHE_SCHEDULE
   /* search schedule in communicator specific tree */

ompi/mca/coll/libnbc/nbc_iallreduce.c

@@ -7,7 +7,7 @@
  *                         rights reserved.
  * Copyright (c) 2013-2015 Los Alamos National Security, LLC. All rights
  *                         reserved.
- * Copyright (c) 2014-2016 Research Organization for Information Science
+ * Copyright (c) 2014-2017 Research Organization for Information Science
  *                         and Technology (RIST). All rights reserved.
  *
  * Author(s): Torsten Hoefler <htor@cs.indiana.edu>
@@ -82,6 +82,19 @@ int ompi_coll_libnbc_iallreduce(const void* sendbuf, void* recvbuf, int count, M
     return res;
   }
 
+  if (1 == p) {
+    if (!inplace) {
+      /* for a single node - copy data to receivebuf */
+      res = NBC_Copy(sendbuf, count, datatype, recvbuf, count, datatype, comm);
+      if (OPAL_UNLIKELY(OMPI_SUCCESS != res)) {
+        NBC_Return_handle (handle);
+        return res;
+      }
+    }
+    *request = &ompi_request_empty;
+    return OMPI_SUCCESS;
+  }
+
   res = NBC_Init_handle (comm, &handle, libnbc_module);
   if (OPAL_UNLIKELY(OMPI_SUCCESS != res)) {
     return res;
@@ -94,15 +107,6 @@ int ompi_coll_libnbc_iallreduce(const void* sendbuf, void* recvbuf, int count, M
     return OMPI_ERR_OUT_OF_RESOURCE;
   }
 
-  if ((p == 1) && !inplace) {
-    /* for a single node - copy data to receivebuf */
-    res = NBC_Copy(sendbuf, count, datatype, recvbuf, count, datatype, comm);
-    if (OPAL_UNLIKELY(OMPI_SUCCESS != res)) {
-      NBC_Return_handle (handle);
-      return res;
-    }
-  }
-
   /* algorithm selection */
   if(p < 4 || size*count < 65536 || !ompi_op_is_commute(op) || inplace) {
     alg = NBC_ARED_BINOMIAL;

ompi/mca/coll/libnbc/nbc_ibcast.c

@@ -5,7 +5,7 @@
  *                         Corporation.  All rights reserved.
  * Copyright (c) 2006      The Technical University of Chemnitz. All
  *                         rights reserved.
- * Copyright (c) 2014-2015 Research Organization for Information Science
+ * Copyright (c) 2014-2017 Research Organization for Information Science
  *                         and Technology (RIST). All rights reserved.
  * Copyright (c) 2015      Los Alamos National Security, LLC. All rights
  *                         reserved.
@@ -58,6 +58,11 @@ int ompi_coll_libnbc_ibcast(void *buffer, int count, MPI_Datatype datatype, int
   rank = ompi_comm_rank (comm);
   p = ompi_comm_size (comm);
 
+  if (1 == p) {
+    *request = &ompi_request_empty;
+    return OMPI_SUCCESS;
+  }
+
   res = ompi_datatype_type_size(datatype, &size);
   if (MPI_SUCCESS != res) {
     NBC_Error("MPI Error in ompi_datatype_type_size() (%i)", res);

ompi/mca/coll/libnbc/nbc_ireduce.c

@@ -7,7 +7,7 @@
  *                         rights reserved.
  * Copyright (c) 2013-2015 Los Alamos National Security, LLC. All rights
  *                         reserved.
- * Copyright (c) 2014-2016 Research Organization for Information Science
+ * Copyright (c) 2014-2017 Research Organization for Information Science
  *                         and Technology (RIST). All rights reserved.
  *
  * Author(s): Torsten Hoefler <htor@cs.indiana.edu>
@@ -80,12 +80,13 @@ int ompi_coll_libnbc_ireduce(const void* sendbuf, void* recvbuf, int count, MPI_
   }
 
   /* only one node -> copy data */
-  if ((p == 1) && !inplace) {
+  if (p == 1) {
+    if (!inplace) {
       res = NBC_Copy (sendbuf, count, datatype, recvbuf, count, datatype, comm);
       if (OPAL_UNLIKELY(OMPI_SUCCESS != res)) {
         return res;
       }
-
+    }
     *request = &ompi_request_empty;
     return OMPI_SUCCESS;
   }