Improvement for IBARRIER when number of processes is 1.

When number of processes is only 1, we do not need to schedule
the current NBC communication but can just return a REQUEST_NULL
request handle. This patch fixes this issue.

Signed-off-by: Pavan Balaji <balaji@anl.gov>

src/mpi/coll/ibarrier.c

@@ -190,19 +190,21 @@ int MPIR_Ibarrier_impl(MPID_Comm *comm_ptr, MPI_Request *request)
         /* --END USEREXTENSION-- */
     }
 
-    mpi_errno = MPID_Sched_next_tag(comm_ptr, &tag);
-    if (mpi_errno) MPIU_ERR_POP(mpi_errno);
-    mpi_errno = MPID_Sched_create(&s);
-    if (mpi_errno) MPIU_ERR_POP(mpi_errno);
+    if (comm_ptr->local_size != 1) {
+        mpi_errno = MPID_Sched_next_tag(comm_ptr, &tag);
+        if (mpi_errno) MPIU_ERR_POP(mpi_errno);
+        mpi_errno = MPID_Sched_create(&s);
+        if (mpi_errno) MPIU_ERR_POP(mpi_errno);
 
-    MPIU_Assert(comm_ptr->coll_fns->Ibarrier_sched != NULL);
-    mpi_errno = comm_ptr->coll_fns->Ibarrier_sched(comm_ptr, s);
-    if (mpi_errno) MPIU_ERR_POP(mpi_errno);
+        MPIU_Assert(comm_ptr->coll_fns->Ibarrier_sched != NULL);
+        mpi_errno = comm_ptr->coll_fns->Ibarrier_sched(comm_ptr, s);
+        if (mpi_errno) MPIU_ERR_POP(mpi_errno);
 
-    mpi_errno = MPID_Sched_start(&s, comm_ptr, tag, &reqp);
-    if (reqp)
-        *request = reqp->handle;
-    if (mpi_errno) MPIU_ERR_POP(mpi_errno);
+        mpi_errno = MPID_Sched_start(&s, comm_ptr, tag, &reqp);
+        if (reqp)
+            *request = reqp->handle;
+        if (mpi_errno) MPIU_ERR_POP(mpi_errno);
+    }
 
 fn_exit:
     return mpi_errno;

src/mpid/ch3/src/ch3u_rma_sync.c

@@ -537,9 +537,15 @@ int MPIDI_Win_fence(int assert, MPID_Win * win_ptr)
             if (mpi_errno != MPI_SUCCESS)
                 MPIU_ERR_POP(mpi_errno);
 
-            /* Set window access state properly. */
-            win_ptr->states.access_state = MPIDI_RMA_FENCE_ISSUED;
-            MPIDI_CH3I_num_active_issued_win++;
+            if (win_ptr->fence_sync_req == MPI_REQUEST_NULL) {
+                /* ibarrier completed immediately. */
+                win_ptr->states.access_state = MPIDI_RMA_FENCE_GRANTED;
+            }
+            else {
+                /* Set window access state properly. */
+                win_ptr->states.access_state = MPIDI_RMA_FENCE_ISSUED;
+                MPIDI_CH3I_num_active_issued_win++;
+            }
 
             goto finish_fence;
         }
@@ -644,8 +650,15 @@ int MPIDI_Win_fence(int assert, MPID_Win * win_ptr)
             mpi_errno = MPIR_Ibarrier_impl(win_ptr->comm_ptr, &(win_ptr->fence_sync_req));
             if (mpi_errno != MPI_SUCCESS)
                 MPIU_ERR_POP(mpi_errno);
-            MPIDI_CH3I_num_active_issued_win++;
-            win_ptr->states.access_state = MPIDI_RMA_FENCE_ISSUED;
+
+            if (win_ptr->fence_sync_req == MPI_REQUEST_NULL) {
+                /* ibarrier completed immediately. */
+                win_ptr->states.access_state = MPIDI_RMA_FENCE_GRANTED;
+            }
+            else {
+                MPIDI_CH3I_num_active_issued_win++;
+                win_ptr->states.access_state = MPIDI_RMA_FENCE_ISSUED;
+            }
 
             if (win_ptr->shm_allocated == TRUE) {
                 MPID_Comm *node_comm_ptr = win_ptr->comm_ptr->node_comm;