From: Martin Kronbichler <kronbichler@lnm.mw.tum.de>
Date: Thu, 14 Nov 2019 20:24:03 +0000 (+0100)
Subject: Fix two places where we used too large numbers in communication channel
X-Git-Tag: v9.2.0-rc1~872^2
X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=22647fb2799a2925bef3b4e9dd34cceb8a0c1754;p=dealii.git

Fix two places where we used too large numbers in communication channel
---

diff --git a/include/deal.II/lac/la_parallel_block_vector.templates.h b/include/deal.II/lac/la_parallel_block_vector.templates.h
index 663e2421f8..9666fe25e0 100644
--- a/include/deal.II/lac/la_parallel_block_vector.templates.h
+++ b/include/deal.II/lac/la_parallel_block_vector.templates.h
@@ -289,10 +289,10 @@ namespace LinearAlgebra
 
           // In order to avoid conflict with possible other ongoing
           // communication requests (from LA::distributed::Vector that supports
-          // unfinished requests), add an arbitrary number 9923 to the
-          // communication tag
+          // unfinished requests), add 100 to the communication tag (the first
+          // 100 can be used by normal vectors)
           for (unsigned int block = start; block < end; ++block)
-            this->block(block).update_ghost_values_start(block - start + 9923);
+            this->block(block).update_ghost_values_start(block - start + 100);
           for (unsigned int block = start; block < end; ++block)
             this->block(block).update_ghost_values_finish();
         }
diff --git a/include/deal.II/matrix_free/matrix_free.h b/include/deal.II/matrix_free/matrix_free.h
index ef0003be65..4ccd2b38cd 100644
--- a/include/deal.II/matrix_free/matrix_free.h
+++ b/include/deal.II/matrix_free/matrix_free.h
@@ -2923,10 +2923,12 @@ namespace internal
   template <int dim, typename Number, typename VectorizedArrayType>
   struct VectorDataExchange
   {
-    // An arbitrary shift for communication to reduce the risk for accidental
+    // A shift for the MPI messages to reduce the risk for accidental
     // interaction with other open communications that a user program might
-    // set up
-    static constexpr unsigned int channel_shift = 103;
+    // set up (parallel vectors support unfinished communication). We let
+    // the other vectors use the first 20 assigned numbers and start the
+    // matrix-free communication.
+    static constexpr unsigned int channel_shift = 20;