From b0ef650a12be6f6af290964e888525cb70d0252a Mon Sep 17 00:00:00 2001
From: Mark Olesen <Mark.Olesen@esi-group.com>
Date: Mon, 14 Feb 2022 12:12:32 +0100
Subject: [PATCH] ENH: Pstream specialization for float/scalar, FixedList
 (#2351)

- native MPI min/max/sum reductions for float/double
  irrespective of WM_PRECISION_OPTION

- native MPI min/max/sum reductions for (u)int32_t/(u)int64_t types,
  irrespective of WM_LABEL_SIZE

- replace rarely used vector2D sum reduction with FixedList as a
  indicator of its intent and also generalizes to different lengths.

  OLD:
      vector2D values;  values.x() = ...;  values.y() = ...;
      reduce(values, sumOp<vector2D>());

  NEW:
      FixedList<scalar,2> values;  values[0] = ...;  values[1] = ...;
      reduce(values, sumOp<scalar>());

- allow returnReduce() to use native reductions. Previous code (with
  linear/tree selector) would have bypassed them inadvertently.

ENH: added support for MPI broadcast (for a memory span)

ENH: select communication schedule as a static method

- UPstream::whichCommunication(comm) to select linear/tree
  communication instead of ternary or
  if (Pstream::nProcs() < Pstream::nProcsSimpleSum) ...

STYLE: align nProcsSimpleSum static value with etc/controlDict override
---
 .../Test-parallel-communicators.C             |  10 -
 .../Pstreams/PstreamCombineReduceOps.H        |  45 +--
 .../db/IOstreams/Pstreams/PstreamReduceOps.H  | 311 ++++++++++--------
 src/OpenFOAM/db/IOstreams/Pstreams/UPstream.C |   4 +-
 src/OpenFOAM/db/IOstreams/Pstreams/UPstream.H |  44 ++-
 .../IOstreams/Pstreams/combineGatherScatter.C | 155 +++------
 .../db/IOstreams/Pstreams/gatherScatter.C     |  20 +-
 .../db/IOstreams/Pstreams/gatherScatterList.C |  20 +-
 .../masterUncollatedFileOperation.C           |  18 +-
 .../uncollatedFileOperation.C                 |   9 +-
 .../lduMatrix/solvers/GAMG/GAMGSolverScale.C  |  20 +-
 src/Pstream/dummy/Make/files                  |   2 +
 src/Pstream/dummy/UPstream.C                  |  97 +-----
 src/Pstream/dummy/UPstreamBroadcast.C         |  45 +++
 src/Pstream/dummy/UPstreamReduce.C            | 153 +++++++++
 src/Pstream/mpi/Make/files                    |   2 +
 src/Pstream/mpi/PstreamGlobals.H              |   8 +-
 src/Pstream/mpi/UPstream.C                    | 297 +----------------
 src/Pstream/mpi/UPstreamBroadcast.C           |  93 ++++++
 src/Pstream/mpi/UPstreamReduce.C              | 211 ++++++++++++
 src/Pstream/mpi/allReduce.H                   |  45 ++-
 src/Pstream/mpi/allReduceTemplates.C          | 214 +++++-------
 .../patchMeanVelocityForce.C                  |  39 +--
 .../state/lumpedPointState.C                  |  10 +-
 24 files changed, 932 insertions(+), 940 deletions(-)
 create mode 100644 src/Pstream/dummy/UPstreamBroadcast.C
 create mode 100644 src/Pstream/dummy/UPstreamReduce.C
 create mode 100644 src/Pstream/mpi/UPstreamBroadcast.C
 create mode 100644 src/Pstream/mpi/UPstreamReduce.C

diff --git a/applications/test/parallel-communicators/Test-parallel-communicators.C b/applications/test/parallel-communicators/Test-parallel-communicators.C
index 99a3158d06..6c4662d011 100644
--- a/applications/test/parallel-communicators/Test-parallel-communicators.C
+++ b/applications/test/parallel-communicators/Test-parallel-communicators.C
@@ -163,16 +163,6 @@ int main(int argc, char *argv[])
 
     if (Pstream::myProcNo(comm) != -1)
     {
-        //scalar sum = sumReduce(comm, localValue);
-        //scalar sum = localValue;
-        //reduce
-        //(
-        //    UPstream::treeCommunication(comm),
-        //    sum,
-        //    sumOp<scalar>(),
-        //    Pstream::msgType(),
-        //    comm
-        //);
         scalar sum = returnReduce
         (
             localValue,
diff --git a/src/OpenFOAM/db/IOstreams/Pstreams/PstreamCombineReduceOps.H b/src/OpenFOAM/db/IOstreams/Pstreams/PstreamCombineReduceOps.H
index 23dd721a11..7ab8c9dbd9 100644
--- a/src/OpenFOAM/db/IOstreams/Pstreams/PstreamCombineReduceOps.H
+++ b/src/OpenFOAM/db/IOstreams/Pstreams/PstreamCombineReduceOps.H
@@ -35,8 +35,8 @@ Description
 
 \*---------------------------------------------------------------------------*/
 
-#ifndef PstreamCombineReduceOps_H
-#define PstreamCombineReduceOps_H
+#ifndef Foam_PstreamCombineReduceOps_H
+#define Foam_PstreamCombineReduceOps_H
 
 #include "UPstream.H"
 #include "Pstream.H"
@@ -73,42 +73,11 @@ void combineReduce
     const label comm = Pstream::worldComm
 )
 {
-    if (UPstream::nProcs(comm) < UPstream::nProcsSimpleSum)
-    {
-        Pstream::combineGather
-        (
-            UPstream::linearCommunication(comm),
-            Value,
-            cop,
-            tag,
-            comm
-        );
-        Pstream::combineScatter
-        (
-            UPstream::linearCommunication(comm),
-            Value,
-            tag,
-            comm
-        );
-    }
-    else
-    {
-        Pstream::combineGather
-        (
-            UPstream::treeCommunication(comm),
-            Value,
-            cop,
-            tag,
-            comm
-        );
-        Pstream::combineScatter
-        (
-            UPstream::treeCommunication(comm),
-            Value,
-            tag,
-            comm
-        );
-    }
+    const List<UPstream::commsStruct>& comms =
+        UPstream::whichCommunication(comm);
+
+    Pstream::combineGather(comms, Value, cop, tag, comm);
+    Pstream::combineScatter(comms, Value, tag, comm);
 }
 
 
diff --git a/src/OpenFOAM/db/IOstreams/Pstreams/PstreamReduceOps.H b/src/OpenFOAM/db/IOstreams/Pstreams/PstreamReduceOps.H
index 2741d562bd..669a37d248 100644
--- a/src/OpenFOAM/db/IOstreams/Pstreams/PstreamReduceOps.H
+++ b/src/OpenFOAM/db/IOstreams/Pstreams/PstreamReduceOps.H
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2016 OpenFOAM Foundation
-    Copyright (C) 2016 OpenCFD Ltd.
+    Copyright (C) 2016-2022 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -32,11 +32,11 @@ Description
 
 \*---------------------------------------------------------------------------*/
 
-#ifndef PstreamReduceOps_H
-#define PstreamReduceOps_H
+#ifndef Foam_PstreamReduceOps_H
+#define Foam_PstreamReduceOps_H
 
 #include "ops.H"
-#include "vector2D.H"
+#include "FixedList.H"
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
@@ -45,12 +45,12 @@ namespace Foam
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
-// Reduce operation with user specified communication schedule
+//- Reduce operation with user specified communication schedule
 template<class T, class BinaryOp>
 void reduce
 (
     const List<UPstream::commsStruct>& comms,
-    T& Value,
+    T& value,
     const BinaryOp& bop,
     const int tag,
     const label comm
@@ -58,96 +58,86 @@ void reduce
 {
     if (UPstream::warnComm != -1 && comm != UPstream::warnComm)
     {
-        Pout<< "** reducing:" << Value << " with comm:" << comm
+        Pout<< "** reducing:" << value << " with comm:" << comm
             << endl;
         error::printStack(Pout);
     }
-    Pstream::gather(comms, Value, bop, tag, comm);
-    Pstream::scatter(comms, Value, tag, comm);
+    Pstream::gather(comms, value, bop, tag, comm);
+    Pstream::scatter(comms, value, tag, comm);
 }
 
 
-// Reduce using either linear or tree communication schedule
+//- Reduce (inplace) using either linear or tree communication schedule
 template<class T, class BinaryOp>
 void reduce
 (
-    T& Value,
+    T& value,
     const BinaryOp& bop,
-    const int tag = Pstream::msgType(),
+    const int tag = UPstream::msgType(),
     const label comm = UPstream::worldComm
 )
 {
-    if (UPstream::nProcs(comm) < UPstream::nProcsSimpleSum)
+    if (UPstream::parRun())
     {
-        reduce(UPstream::linearCommunication(comm), Value, bop, tag, comm);
-    }
-    else
-    {
-        reduce(UPstream::treeCommunication(comm), Value, bop, tag, comm);
+        reduce(UPstream::whichCommunication(comm), value, bop, tag, comm);
     }
 }
 
 
-// Reduce using either linear or tree communication schedule
+//- Reduce (copy) and return value
 template<class T, class BinaryOp>
 T returnReduce
 (
-    const T& Value,
+    const T& value,
     const BinaryOp& bop,
-    const int tag = Pstream::msgType(),
+    const int tag = UPstream::msgType(),
     const label comm = UPstream::worldComm
 )
 {
-    T WorkValue(Value);
-
-    if (UPstream::nProcs(comm) < UPstream::nProcsSimpleSum)
-    {
-        reduce
-        (
-            UPstream::linearCommunication(comm),
-            WorkValue,
-            bop,
-            tag,
-            comm
-        );
-    }
-    else
-    {
-        reduce
-        (
-            UPstream::treeCommunication(comm),
-            WorkValue,
-            bop,
-            tag,
-            comm
-        );
-    }
-
-    return WorkValue;
+    T work(value);
+    reduce(work, bop, tag, comm);
+    return work;
 }
 
 
-// Reduce with sum of both value and count (for averaging)
+//- Reduce with sum of both value and count (for averaging)
 template<class T>
 void sumReduce
 (
-    T& Value,
-    label& Count,
-    const int tag = Pstream::msgType(),
+    T& value,
+    label& count,
+    const int tag = UPstream::msgType(),
     const label comm = UPstream::worldComm
 )
 {
-    reduce(Value, sumOp<T>(), tag, comm);
-    reduce(Count, sumOp<label>(), tag, comm);
+    if (UPstream::parRun())
+    {
+        reduce(value, sumOp<T>(), tag, comm);
+        reduce(count, sumOp<label>(), tag, comm);
+    }
 }
 
 
-// Non-blocking version of reduce. Sets request.
+//- Reduce multiple values (identical size on all processes!)
+template<class T, class BinaryOp>
+void reduce
+(
+    T values[],
+    const int size,
+    const BinaryOp&,
+    const int tag,
+    const label comm
+)
+{
+    NotImplemented;
+}
+
+//- Non-blocking reduce single value. Sets request.
 template<class T, class BinaryOp>
 void reduce
 (
     T& Value,
-    const BinaryOp& bop,
+    const BinaryOp&,
     const int tag,
     const label comm,
     label& request
@@ -156,13 +146,14 @@ void reduce
     NotImplemented;
 }
 
-// Non-blocking version of reduce. Sets request.
+//- Non-blocking reduce multiple values (identical size on all processes!)
+//- Sets request.
 template<class T, class BinaryOp>
 void reduce
 (
-    T Value[],
+    T values[],
     const int size,
-    const BinaryOp& bop,
+    const BinaryOp&,
     const int tag,
     const label comm,
     label& request
@@ -172,111 +163,139 @@ void reduce
 }
 
 
-// Insist there are specialisations for the common reductions of scalar(s)
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+// Specialisations for bool
+
+//- Logical (and) reduction
 void reduce
 (
-    scalar& Value,
-    const sumOp<scalar>& bop,
-    const int tag = Pstream::msgType(),
+    bool& value,
+    const andOp<bool>&,
+    const int tag = UPstream::msgType(),
     const label comm = UPstream::worldComm
 );
 
+//- Logical (or) reduction
 void reduce
 (
-    scalar& Value,
-    const minOp<scalar>& bop,
-    const int tag = Pstream::msgType(),
+    bool& value,
+    const orOp<bool>&,
+    const int tag = UPstream::msgType(),
     const label comm = UPstream::worldComm
 );
 
-void reduce
-(
-    vector2D& Value,
-    const sumOp<vector2D>& bop,
-    const int tag = Pstream::msgType(),
-    const label comm = UPstream::worldComm
-);
 
-void sumReduce
-(
-    scalar& Value,
-    label& Count,
-    const int tag = Pstream::msgType(),
-    const label comm = UPstream::worldComm
-);
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
-void reduce
-(
-    scalar& Value,
-    const sumOp<scalar>& bop,
-    const int tag,
-    const label comm,
-    label& request
-);
+// Specialisations for common reduction types
 
-void reduce
-(
-    scalar Value[],
-    const int size,
-    const sumOp<scalar>& bop,
-    const int tag,
-    const label comm,
-    label& request
+#undef  Pstream_CommonReductions
+#define Pstream_CommonReductions(Native)                                      \
+                                                                              \
+/*! \brief Reduce (min) single Native value */                                \
+void reduce                                                                   \
+(                                                                             \
+    Native& value,                                                            \
+    const minOp<Native>&,                                                     \
+    const int tag = UPstream::msgType(),                                      \
+    const label comm = UPstream::worldComm                                    \
+);                                                                            \
+                                                                              \
+/*! \brief Reduce (max) single Native value */                                \
+void reduce                                                                   \
+(                                                                             \
+    Native& value,                                                            \
+    const maxOp<Native>&,                                                     \
+    const int tag = UPstream::msgType(),                                      \
+    const label comm = UPstream::worldComm                                    \
+);                                                                            \
+                                                                              \
+/*! \brief Reduce (sum) single Native value */                                \
+void reduce                                                                   \
+(                                                                             \
+    Native& value,                                                            \
+    const sumOp<Native>&,                                                     \
+    const int tag = UPstream::msgType(),                                      \
+    const label comm = UPstream::worldComm                                    \
+);                                                                            \
+                                                                              \
+/*! \brief Reduce (sum) multiple Native values (identical size all procs!) */ \
+void reduce                                                                   \
+(                                                                             \
+    Native values[],                                                          \
+    const int size,                                                           \
+    const sumOp<Native>&,                                                     \
+    const int tag,                                                            \
+    const label comm                                                          \
+);                                                                            \
+                                                                              \
+/*! \brief Reduce (sum) multiple Native values */                             \
+template<unsigned N>                                                          \
+inline void reduce                                                            \
+(                                                                             \
+    FixedList<Native, N>& values,                                             \
+    const sumOp<Native>&,                                                     \
+    const int tag = UPstream::msgType(),                                      \
+    const label comm = UPstream::worldComm                                    \
+)                                                                             \
+{                                                                             \
+    reduce(values.data(), int(values.size()), sumOp<Native>(), tag, comm);    \
+}
+
+
+Pstream_CommonReductions(int32_t);
+Pstream_CommonReductions(int64_t);
+Pstream_CommonReductions(uint32_t);
+Pstream_CommonReductions(uint64_t);
+Pstream_CommonReductions(float);
+Pstream_CommonReductions(double);
+
+#undef Pstream_CommonReductions
+
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+// Specialisations for floating-point types
+
+#undef  Pstream_FloatReductions
+#define Pstream_FloatReductions(Native)                                       \
+                                                                              \
+/*! \brief Sum of both Native value and count (for averaging) */              \
+void sumReduce                                                                \
+(                                                                             \
+    Native& value,                                                            \
+    label& count,                                                             \
+    const int tag = UPstream::msgType(),                                      \
+    const label comm = UPstream::worldComm                                    \
+);                                                                            \
+                                                                              \
+/*! \brief Non-blocking reduce (sum) single Native value. Sets request */     \
+void reduce                                                                   \
+(                                                                             \
+    Native& value,                                                            \
+    const sumOp<Native>&,                                                     \
+    const int tag,                                                            \
+    const label comm,                                                         \
+    label& requestID                                                          \
+);                                                                            \
+                                                                              \
+/*! \brief Non-blocking reduce (sum) multiple Native values. Sets request */  \
+void reduce                                                                   \
+(                                                                             \
+    Native values[],                                                          \
+    const int size,                                                           \
+    const sumOp<Native>&,                                                     \
+    const int tag,                                                            \
+    const label comm,                                                         \
+    label& requestID                                                          \
 );
 
 
-#if defined(WM_SPDP)
-void reduce
-(
-    solveScalar& Value,
-    const sumOp<solveScalar>& bop,
-    const int tag = Pstream::msgType(),
-    const label comm = UPstream::worldComm
-);
+Pstream_FloatReductions(float);
+Pstream_FloatReductions(double);
 
-void reduce
-(
-    solveScalar& Value,
-    const minOp<solveScalar>& bop,
-    const int tag = Pstream::msgType(),
-    const label comm = UPstream::worldComm
-);
-
-void reduce
-(
-    Vector2D<solveScalar>& Value,
-    const sumOp<Vector2D<solveScalar>>& bop,
-    const int tag = Pstream::msgType(),
-    const label comm = UPstream::worldComm
-);
-
-void sumReduce
-(
-    solveScalar& Value,
-    label& Count,
-    const int tag = Pstream::msgType(),
-    const label comm = UPstream::worldComm
-);
-
-void reduce
-(
-    solveScalar& Value,
-    const sumOp<solveScalar>& bop,
-    const int tag,
-    const label comm,
-    label& request
-);
-
-void reduce
-(
-    solveScalar Value[],
-    const int size,
-    const sumOp<solveScalar>& bop,
-    const int tag,
-    const label comm,
-    label& request
-);
-#endif
+#undef Pstream_FloatReductions
 
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
diff --git a/src/OpenFOAM/db/IOstreams/Pstreams/UPstream.C b/src/OpenFOAM/db/IOstreams/Pstreams/UPstream.C
index 936a50db55..37ec9d5740 100644
--- a/src/OpenFOAM/db/IOstreams/Pstreams/UPstream.C
+++ b/src/OpenFOAM/db/IOstreams/Pstreams/UPstream.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2017 OpenFOAM Foundation
-    Copyright (C) 2015-2021 OpenCFD Ltd.
+    Copyright (C) 2015-2022 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -414,7 +414,7 @@ registerOptSwitch
 
 int Foam::UPstream::nProcsSimpleSum
 (
-    Foam::debug::optimisationSwitch("nProcsSimpleSum", 16)
+    Foam::debug::optimisationSwitch("nProcsSimpleSum", 0)
 );
 registerOptSwitch
 (
diff --git a/src/OpenFOAM/db/IOstreams/Pstreams/UPstream.H b/src/OpenFOAM/db/IOstreams/Pstreams/UPstream.H
index 945bb60559..44310c4c0d 100644
--- a/src/OpenFOAM/db/IOstreams/Pstreams/UPstream.H
+++ b/src/OpenFOAM/db/IOstreams/Pstreams/UPstream.H
@@ -69,9 +69,9 @@ public:
     //- Types of communications
     enum class commsTypes : char
     {
-        blocking,
-        scheduled,
-        nonBlocking
+        blocking,       //!< "blocking"
+        scheduled,      //!< "scheduled"
+        nonBlocking     //!< "nonBlocking"
     };
 
     //- Names of the communication types
@@ -198,7 +198,7 @@ private:
         static labelList worldIDs_;
 
 
-        // Communicator specific data
+    // Communicator specific data
 
         //- My processor number
         static DynamicList<int> myProcNo_;
@@ -413,11 +413,11 @@ public:
 
             static int allocateTag(const char*);
 
-            static int allocateTag(const word&);
+            static int allocateTag(const std::string&);
 
             static void freeTag(const char*, const int tag);
 
-            static void freeTag(const word&, const int tag);
+            static void freeTag(const std::string&, const int tag);
 
 
         //- Set as parallel run on/off.
@@ -537,13 +537,28 @@ public:
             return treeCommunication_[communicator];
         }
 
+        //- Communication schedule for linear/tree all-to-master (proc 0).
+        //- Chooses based on the value of UPstream::nProcsSimpleSum
+        static const List<commsStruct>& whichCommunication
+        (
+            const label communicator = worldComm
+        )
+        {
+            return
+            (
+                nProcs(communicator) < nProcsSimpleSum
+              ? linearCommunication_[communicator]
+              : treeCommunication_[communicator]
+            );
+        }
+
+
         //- Message tag of standard messages
         static int& msgType() noexcept
         {
             return msgType_;
         }
 
-
         //- Get the communications type of the stream
         commsTypes commsType() const noexcept
         {
@@ -551,6 +566,7 @@ public:
         }
 
         //- Set the communications type of the stream
+        //  \return the previous value
         commsTypes commsType(const commsTypes ct) noexcept
         {
             commsTypes old(commsType_);
@@ -668,6 +684,20 @@ public:
         );
 
 
+
+    // Broadcast Functions
+
+        //- Broadcast buffer contents, sizes must match on processors
+        //  \return True on success
+        static bool broadcast
+        (
+            char* buf,
+            const std::streamsize bufSize,
+            const label communicator = worldComm,
+            const int rootProcNo = masterNo()
+        );
+
+
     // Housekeeping
 
         //- Process index of first sub-process
diff --git a/src/OpenFOAM/db/IOstreams/Pstreams/combineGatherScatter.C b/src/OpenFOAM/db/IOstreams/Pstreams/combineGatherScatter.C
index e1c4f0cfc8..19a08cd4c0 100644
--- a/src/OpenFOAM/db/IOstreams/Pstreams/combineGatherScatter.C
+++ b/src/OpenFOAM/db/IOstreams/Pstreams/combineGatherScatter.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2017 OpenFOAM Foundation
-    Copyright (C) 2019-2021 OpenCFD Ltd.
+    Copyright (C) 2019-2022 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -153,28 +153,14 @@ void Foam::Pstream::combineGather
     const label comm
 )
 {
-    if (UPstream::nProcs(comm) < UPstream::nProcsSimpleSum)
-    {
-        combineGather
-        (
-            UPstream::linearCommunication(comm),
-            Value,
-            cop,
-            tag,
-            comm
-        );
-    }
-    else
-    {
-        combineGather
-        (
-            UPstream::treeCommunication(comm),
-            Value,
-            cop,
-            tag,
-            comm
-        );
-    }
+    combineGather
+    (
+        UPstream::whichCommunication(comm),
+        Value,
+        cop,
+        tag,
+        comm
+    );
 }
 
 
@@ -274,14 +260,7 @@ void Foam::Pstream::combineScatter
     const label comm
 )
 {
-    if (UPstream::nProcs(comm) < UPstream::nProcsSimpleSum)
-    {
-        combineScatter(UPstream::linearCommunication(comm), Value, tag, comm);
-    }
-    else
-    {
-        combineScatter(UPstream::treeCommunication(comm), Value, tag, comm);
-    }
+    combineScatter(UPstream::whichCommunication(comm), Value, tag, comm);
 }
 
 
@@ -402,28 +381,14 @@ void Foam::Pstream::listCombineGather
     const label comm
 )
 {
-    if (UPstream::nProcs(comm) < UPstream::nProcsSimpleSum)
-    {
-        listCombineGather
-        (
-            UPstream::linearCommunication(comm),
-            Values,
-            cop,
-            tag,
-            comm
-        );
-    }
-    else
-    {
-        listCombineGather
-        (
-            UPstream::treeCommunication(comm),
-            Values,
-            cop,
-            tag,
-            comm
-        );
-    }
+    listCombineGather
+    (
+        UPstream::whichCommunication(comm),
+        Values,
+        cop,
+        tag,
+        comm
+    );
 }
 
 
@@ -523,26 +488,13 @@ void Foam::Pstream::listCombineScatter
     const label comm
 )
 {
-    if (UPstream::nProcs(comm) < UPstream::nProcsSimpleSum)
-    {
-        listCombineScatter
-        (
-            UPstream::linearCommunication(comm),
-            Values,
-            tag,
-            comm
-        );
-    }
-    else
-    {
-        listCombineScatter
-        (
-            UPstream::treeCommunication(comm),
-            Values,
-            tag,
-            comm
-        );
-    }
+    listCombineScatter
+    (
+        UPstream::whichCommunication(comm),
+        Values,
+        tag,
+        comm
+    );
 }
 
 
@@ -636,28 +588,14 @@ void Foam::Pstream::mapCombineGather
     const label comm
 )
 {
-    if (UPstream::nProcs(comm) < UPstream::nProcsSimpleSum)
-    {
-        mapCombineGather
-        (
-            UPstream::linearCommunication(comm),
-            Values,
-            cop,
-            tag,
-            comm
-        );
-    }
-    else
-    {
-        mapCombineGather
-        (
-            UPstream::treeCommunication(comm),
-            Values,
-            cop,
-            tag,
-            comm
-        );
-    }
+    mapCombineGather
+    (
+        UPstream::whichCommunication(comm),
+        Values,
+        cop,
+        tag,
+        comm
+    );
 }
 
 
@@ -727,26 +665,13 @@ void Foam::Pstream::mapCombineScatter
     const label comm
 )
 {
-    if (UPstream::nProcs(comm) < UPstream::nProcsSimpleSum)
-    {
-        mapCombineScatter
-        (
-            UPstream::linearCommunication(comm),
-            Values,
-            tag,
-            comm
-        );
-    }
-    else
-    {
-        mapCombineScatter
-        (
-            UPstream::treeCommunication(comm),
-            Values,
-            tag,
-            comm
-        );
-    }
+    mapCombineScatter
+    (
+        UPstream::whichCommunication(comm),
+        Values,
+        tag,
+        comm
+    );
 }
 
 
diff --git a/src/OpenFOAM/db/IOstreams/Pstreams/gatherScatter.C b/src/OpenFOAM/db/IOstreams/Pstreams/gatherScatter.C
index e4457ff2ec..6eea209698 100644
--- a/src/OpenFOAM/db/IOstreams/Pstreams/gatherScatter.C
+++ b/src/OpenFOAM/db/IOstreams/Pstreams/gatherScatter.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2017 OpenFOAM Foundation
-    Copyright (C) 2019 OpenCFD Ltd.
+    Copyright (C) 2019-2022 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -134,14 +134,7 @@ void Pstream::gather
     const label comm
 )
 {
-    if (UPstream::nProcs(comm) < UPstream::nProcsSimpleSum)
-    {
-        gather(UPstream::linearCommunication(comm), Value, bop, tag, comm);
-    }
-    else
-    {
-        gather(UPstream::treeCommunication(comm), Value, bop, tag, comm);
-    }
+    gather(UPstream::whichCommunication(comm), Value, bop, tag, comm);
 }
 
 
@@ -225,14 +218,7 @@ void Pstream::scatter
 template<class T>
 void Pstream::scatter(T& Value, const int tag, const label comm)
 {
-    if (UPstream::nProcs(comm) < UPstream::nProcsSimpleSum)
-    {
-        scatter(UPstream::linearCommunication(comm), Value, tag, comm);
-    }
-    else
-    {
-        scatter(UPstream::treeCommunication(comm), Value, tag, comm);
-    }
+    scatter(UPstream::whichCommunication(comm), Value, tag, comm);
 }
 
 
diff --git a/src/OpenFOAM/db/IOstreams/Pstreams/gatherScatterList.C b/src/OpenFOAM/db/IOstreams/Pstreams/gatherScatterList.C
index 7de5fd1224..8ad37ff812 100644
--- a/src/OpenFOAM/db/IOstreams/Pstreams/gatherScatterList.C
+++ b/src/OpenFOAM/db/IOstreams/Pstreams/gatherScatterList.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2017 OpenFOAM Foundation
-    Copyright (C) 2015-2021 OpenCFD Ltd.
+    Copyright (C) 2015-2022 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -199,14 +199,7 @@ void Pstream::gatherList
 template<class T>
 void Pstream::gatherList(List<T>& Values, const int tag, const label comm)
 {
-    if (UPstream::nProcs(comm) < UPstream::nProcsSimpleSum)
-    {
-        gatherList(UPstream::linearCommunication(comm), Values, tag, comm);
-    }
-    else
-    {
-        gatherList(UPstream::treeCommunication(comm), Values, tag, comm);
-    }
+    gatherList(UPstream::whichCommunication(comm), Values, tag, comm);
 }
 
 
@@ -341,14 +334,7 @@ void Pstream::scatterList
 template<class T>
 void Pstream::scatterList(List<T>& Values, const int tag, const label comm)
 {
-    if (UPstream::nProcs(comm) < UPstream::nProcsSimpleSum)
-    {
-        scatterList(UPstream::linearCommunication(comm), Values, tag, comm);
-    }
-    else
-    {
-        scatterList(UPstream::treeCommunication(comm), Values, tag, comm);
-    }
+    scatterList(UPstream::whichCommunication(comm), Values, tag, comm);
 }
 
 
diff --git a/src/OpenFOAM/global/fileOperations/masterUncollatedFileOperation/masterUncollatedFileOperation.C b/src/OpenFOAM/global/fileOperations/masterUncollatedFileOperation/masterUncollatedFileOperation.C
index c7babbd03a..01af992088 100644
--- a/src/OpenFOAM/global/fileOperations/masterUncollatedFileOperation/masterUncollatedFileOperation.C
+++ b/src/OpenFOAM/global/fileOperations/masterUncollatedFileOperation/masterUncollatedFileOperation.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2017-2018 OpenFOAM Foundation
-    Copyright (C) 2019-2021 OpenCFD Ltd.
+    Copyright (C) 2019-2022 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -2072,22 +2072,12 @@ bool Foam::fileOperations::masterUncollatedFileOperation::read
         Pstream::scatter(io.note());    //, Pstream::msgType(), comm_);
 
 
-        // scatter operation for regIOobjects
+        // Scatter operation for regIOobjects
 
         // Get my communication order
-        // const List<Pstream::commsStruct>& comms =
-        //(
-        //    (Pstream::nProcs(comm_) < Pstream::nProcsSimpleSum)
-        //  ? Pstream::linearCommunication(comm_)
-        //  : Pstream::treeCommunication(comm_)
-        //);
-        // const Pstream::commsStruct& myComm = comms[Pstream::myProcNo(comm_)];
         const List<Pstream::commsStruct>& comms =
-        (
-            (Pstream::nProcs(Pstream::worldComm) < Pstream::nProcsSimpleSum)
-          ? Pstream::linearCommunication(Pstream::worldComm)
-          : Pstream::treeCommunication(Pstream::worldComm)
-        );
+            Pstream::whichCommunication(Pstream::worldComm);
+
         const Pstream::commsStruct& myComm =
             comms[Pstream::myProcNo(Pstream::worldComm)];
 
diff --git a/src/OpenFOAM/global/fileOperations/uncollatedFileOperation/uncollatedFileOperation.C b/src/OpenFOAM/global/fileOperations/uncollatedFileOperation/uncollatedFileOperation.C
index b1369111f6..f776b013a8 100644
--- a/src/OpenFOAM/global/fileOperations/uncollatedFileOperation/uncollatedFileOperation.C
+++ b/src/OpenFOAM/global/fileOperations/uncollatedFileOperation/uncollatedFileOperation.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2017 OpenFOAM Foundation
-    Copyright (C) 2020-2021 OpenCFD Ltd.
+    Copyright (C) 2020-2022 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -655,12 +655,7 @@ bool Foam::fileOperations::uncollatedFileOperation::read
         Pstream::scatter(io.note());
 
         // Get my communication order
-        const List<Pstream::commsStruct>& comms =
-        (
-            (Pstream::nProcs() < Pstream::nProcsSimpleSum)
-          ? Pstream::linearCommunication()
-          : Pstream::treeCommunication()
-        );
+        const List<Pstream::commsStruct>& comms = Pstream::whichCommunication();
         const Pstream::commsStruct& myComm = comms[Pstream::myProcNo()];
 
         // Receive from up
diff --git a/src/OpenFOAM/matrices/lduMatrix/solvers/GAMG/GAMGSolverScale.C b/src/OpenFOAM/matrices/lduMatrix/solvers/GAMG/GAMGSolverScale.C
index 3563c4738b..b616a1bfe4 100644
--- a/src/OpenFOAM/matrices/lduMatrix/solvers/GAMG/GAMGSolverScale.C
+++ b/src/OpenFOAM/matrices/lduMatrix/solvers/GAMG/GAMGSolverScale.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2017 OpenFOAM Foundation
-    Copyright (C) 2017-2019 OpenCFD Ltd.
+    Copyright (C) 2017-2022 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -27,7 +27,7 @@ License
 \*---------------------------------------------------------------------------*/
 
 #include "GAMGSolver.H"
-#include "vector2D.H"
+#include "FixedList.H"
 
 // * * * * * * * * * * * * * Private Member Functions  * * * * * * * * * * * //
 
@@ -58,21 +58,21 @@ void Foam::GAMGSolver::scale
     const solveScalar* const __restrict__ AcfPtr = Acf.begin();
 
 
-    solveScalar scalingFactorNum = 0.0;
-    solveScalar scalingFactorDenom = 0.0;
+    FixedList<solveScalar, 2> scalingFactor(Zero);
 
     for (label i=0; i<nCells; i++)
     {
-        scalingFactorNum += sourcePtr[i]*fieldPtr[i];
-        scalingFactorDenom += AcfPtr[i]*fieldPtr[i];
+        scalingFactor[0] += fieldPtr[i]*sourcePtr[i];
+        scalingFactor[1] += fieldPtr[i]*AcfPtr[i];
     }
 
-    Vector2D<solveScalar> scalingVector(scalingFactorNum, scalingFactorDenom);
-    A.mesh().reduce(scalingVector, sumOp<Vector2D<solveScalar>>());
+    A.mesh().reduce(scalingFactor, sumOp<solveScalar>());
 
     const solveScalar sf =
-        scalingVector.x()
-       /stabilise(scalingVector.y(), pTraits<solveScalar>::vsmall);
+    (
+        scalingFactor[0]
+      / stabilise(scalingFactor[1], pTraits<solveScalar>::vsmall)
+    );
 
     if (debug >= 2)
     {
diff --git a/src/Pstream/dummy/Make/files b/src/Pstream/dummy/Make/files
index d1d6ee3207..436bf6ffc4 100644
--- a/src/Pstream/dummy/Make/files
+++ b/src/Pstream/dummy/Make/files
@@ -1,4 +1,6 @@
 UPstream.C
+UPstreamBroadcast.C
+UPstreamReduce.C
 
 UIPstreamRead.C
 UOPstreamWrite.C
diff --git a/src/Pstream/dummy/UPstream.C b/src/Pstream/dummy/UPstream.C
index 4f951e09ca..0f73b4b89f 100644
--- a/src/Pstream/dummy/UPstream.C
+++ b/src/Pstream/dummy/UPstream.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2018 OpenFOAM Foundation
-    Copyright (C) 2016-2021 OpenCFD Ltd.
+    Copyright (C) 2016-2022 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -27,7 +27,6 @@ License
 \*---------------------------------------------------------------------------*/
 
 #include "Pstream.H"
-#include "PstreamReduceOps.H"
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
@@ -74,99 +73,7 @@ void Foam::UPstream::abort()
 }
 
 
-void Foam::reduce(scalar&, const sumOp<scalar>&, const int, const label)
-{}
-
-
-void Foam::reduce(scalar&, const minOp<scalar>&, const int, const label)
-{}
-
-
-void Foam::reduce(vector2D&, const sumOp<vector2D>&, const int, const label)
-{}
-
-
-void Foam::sumReduce
-(
-    scalar&,
-    label&,
-    const int,
-    const label
-)
-{}
-
-
-void Foam::reduce(scalar&, const sumOp<scalar>&, const int, const label, label&)
-{}
-
-
-void Foam::reduce
-(
-    scalar[],
-    const int,
-    const sumOp<scalar>&,
-    const int,
-    const label,
-    label&
-)
-{}
-
-
-#if defined(WM_SPDP)
-void Foam::reduce
-(
-    solveScalar& Value,
-    const sumOp<solveScalar>& bop,
-    const int tag,
-    const label comm
-)
-{}
-void Foam::reduce
-(
-    solveScalar& Value,
-    const minOp<solveScalar>& bop,
-    const int tag,
-    const label comm
-)
-{}
-void Foam::reduce
-(
-    Vector2D<solveScalar>& Value,
-    const sumOp<Vector2D<solveScalar>>& bop,
-    const int tag,
-    const label comm
-)
-{}
-void Foam::sumReduce
-(
-    solveScalar& Value,
-    label& Count,
-    const int tag,
-    const label comm
-)
-{}
-void Foam::reduce
-(
-    solveScalar& Value,
-    const sumOp<solveScalar>& bop,
-    const int tag,
-    const label comm,
-    label& request
-)
-{}
-void Foam::reduce
-(
-    solveScalar[],
-    const int,
-    const sumOp<solveScalar>&,
-    const int,
-    const label,
-    label&
-)
-{}
-#endif
-
-
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
 void Foam::UPstream::allToAll
 (
diff --git a/src/Pstream/dummy/UPstreamBroadcast.C b/src/Pstream/dummy/UPstreamBroadcast.C
new file mode 100644
index 0000000000..b4ace0a112
--- /dev/null
+++ b/src/Pstream/dummy/UPstreamBroadcast.C
@@ -0,0 +1,45 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | www.openfoam.com
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+    Copyright (C) 2022 OpenCFD Ltd.
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM.
+
+    OpenFOAM is free software: you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+    for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
+
+\*---------------------------------------------------------------------------*/
+
+#include "UPstream.H"
+
+// * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
+
+bool Foam::UPstream::broadcast
+(
+    char* buf,
+    const std::streamsize bufSize,
+    const label communicator,
+    const int rootProcNo
+)
+{
+    // Nothing to do - ignore
+    return true;
+}
+
+
+// ************************************************************************* //
diff --git a/src/Pstream/dummy/UPstreamReduce.C b/src/Pstream/dummy/UPstreamReduce.C
new file mode 100644
index 0000000000..cef4852701
--- /dev/null
+++ b/src/Pstream/dummy/UPstreamReduce.C
@@ -0,0 +1,153 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | www.openfoam.com
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+    Copyright (C) 2022 OpenCFD Ltd.
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM.
+
+    OpenFOAM is free software: you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+    for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
+
+\*---------------------------------------------------------------------------*/
+
+#include "Pstream.H"
+#include "PstreamReduceOps.H"
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+// Specialisations for bool
+
+void Foam::reduce
+(
+    bool& value,
+    const andOp<bool>&,
+    const int tag,
+    const label comm
+)
+{}
+
+void Foam::reduce
+(
+    bool& value,
+    const orOp<bool>&,
+    const int tag,
+    const label comm
+)
+{}
+
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+// Specialisations for common reduction types
+
+#undef  Pstream_CommonReductions
+#define Pstream_CommonReductions(Native)                                      \
+                                                                              \
+void Foam::reduce                                                             \
+(                                                                             \
+    Native& value,                                                            \
+    const minOp<Native>&,                                                     \
+    const int tag,                                                            \
+    const label comm                                                          \
+)                                                                             \
+{}                                                                            \
+                                                                              \
+void Foam::reduce                                                             \
+(                                                                             \
+    Native& value,                                                            \
+    const maxOp<Native>&,                                                     \
+    const int tag,                                                            \
+    const label comm                                                          \
+)                                                                             \
+{}                                                                            \
+                                                                              \
+void Foam::reduce                                                             \
+(                                                                             \
+    Native& value,                                                            \
+    const sumOp<Native>&,                                                     \
+    const int tag,                                                            \
+    const label comm                                                          \
+)                                                                             \
+{}                                                                            \
+                                                                              \
+void Foam::reduce                                                             \
+(                                                                             \
+    Native values[],                                                          \
+    const int size,                                                           \
+    const sumOp<Native>&,                                                     \
+    const int tag,                                                            \
+    const label comm                                                          \
+)                                                                             \
+{}
+
+
+Pstream_CommonReductions(int32_t);
+Pstream_CommonReductions(int64_t);
+Pstream_CommonReductions(uint32_t);
+Pstream_CommonReductions(uint64_t);
+Pstream_CommonReductions(float);
+Pstream_CommonReductions(double);
+
+#undef Pstream_CommonReductions
+
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+// Specialisations for floating-point types
+
+#undef  Pstream_FloatReductions
+#define Pstream_FloatReductions(Native)                                       \
+                                                                              \
+void Foam::sumReduce                                                          \
+(                                                                             \
+    Native& value,                                                            \
+    label& count,                                                             \
+    const int tag,                                                            \
+    const label comm                                                          \
+)                                                                             \
+{}                                                                            \
+                                                                              \
+void Foam::reduce                                                             \
+(                                                                             \
+    Native& value,                                                            \
+    const sumOp<Native>&,                                                     \
+    const int tag,                                                            \
+    const label comm,                                                         \
+    label& requestID                                                          \
+)                                                                             \
+{}                                                                            \
+                                                                              \
+void Foam::reduce                                                             \
+(                                                                             \
+    Native values[],                                                          \
+    const int size,                                                           \
+    const sumOp<Native>&,                                                     \
+    const int tag,                                                            \
+    const label comm,                                                         \
+    label& requestID                                                          \
+)                                                                             \
+{}
+
+
+Pstream_FloatReductions(float);
+Pstream_FloatReductions(double);
+
+#undef Pstream_FloatReductions
+
+
+// ************************************************************************* //
diff --git a/src/Pstream/mpi/Make/files b/src/Pstream/mpi/Make/files
index e16e96a25f..551d8092bd 100644
--- a/src/Pstream/mpi/Make/files
+++ b/src/Pstream/mpi/Make/files
@@ -1,5 +1,7 @@
 PstreamGlobals.C
 UPstream.C
+UPstreamBroadcast.C
+UPstreamReduce.C
 
 UIPstreamRead.C
 UOPstreamWrite.C
diff --git a/src/Pstream/mpi/PstreamGlobals.H b/src/Pstream/mpi/PstreamGlobals.H
index b3e9501d58..3f80c63a9d 100644
--- a/src/Pstream/mpi/PstreamGlobals.H
+++ b/src/Pstream/mpi/PstreamGlobals.H
@@ -35,8 +35,8 @@ SourceFiles
 
 \*---------------------------------------------------------------------------*/
 
-#ifndef PstreamGlobals_H
-#define PstreamGlobals_H
+#ifndef Foam_PstreamGlobals_H
+#define Foam_PstreamGlobals_H
 
 #include "DynamicList.H"
 #include <mpi.h>
@@ -62,14 +62,12 @@ extern DynamicList<int> freedTags_;
 extern DynamicList<MPI_Comm> MPICommunicators_;
 extern DynamicList<MPI_Group> MPIGroups_;
 
-
 void checkCommunicator(const label comm, const label toProcNo);
 
-};
-
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
+} // End namespace PstreamGlobals
 } // End namespace Foam
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
diff --git a/src/Pstream/mpi/UPstream.C b/src/Pstream/mpi/UPstream.C
index eb9061a842..8b2763bdd2 100644
--- a/src/Pstream/mpi/UPstream.C
+++ b/src/Pstream/mpi/UPstream.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2017 OpenFOAM Foundation
-    Copyright (C) 2016-2021 OpenCFD Ltd.
+    Copyright (C) 2016-2022 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -40,17 +40,6 @@ License
 #include <cstdlib>
 #include <csignal>
 
-#if defined(WM_SP)
-    #define MPI_SCALAR MPI_FLOAT
-    #define MPI_SOLVESCALAR MPI_FLOAT
-#elif defined(WM_SPDP)
-    #define MPI_SCALAR MPI_FLOAT
-    #define MPI_SOLVESCALAR MPI_DOUBLE
-#elif defined(WM_DP)
-    #define MPI_SCALAR MPI_DOUBLE
-    #define MPI_SOLVESCALAR MPI_DOUBLE
-#endif
-
 // * * * * * * * * * * * * * * Static Data Members * * * * * * * * * * * * * //
 
 // The min value and default for MPI buffers length
@@ -491,245 +480,7 @@ void Foam::UPstream::abort()
 }
 
 
-void Foam::reduce
-(
-    scalar& Value,
-    const sumOp<scalar>& bop,
-    const int tag,
-    const label communicator
-)
-{
-    if (UPstream::warnComm != -1 && communicator != UPstream::warnComm)
-    {
-        Pout<< "** reducing:" << Value << " with comm:" << communicator
-            << " warnComm:" << UPstream::warnComm
-            << endl;
-        error::printStack(Pout);
-    }
-    allReduce(Value, 1, MPI_SCALAR, MPI_SUM, bop, tag, communicator);
-}
-
-
-void Foam::reduce
-(
-    scalar& Value,
-    const minOp<scalar>& bop,
-    const int tag,
-    const label communicator
-)
-{
-    if (UPstream::warnComm != -1 && communicator != UPstream::warnComm)
-    {
-        Pout<< "** reducing:" << Value << " with comm:" << communicator
-            << " warnComm:" << UPstream::warnComm
-            << endl;
-        error::printStack(Pout);
-    }
-    allReduce(Value, 1, MPI_SCALAR, MPI_MIN, bop, tag, communicator);
-}
-
-
-void Foam::reduce
-(
-    vector2D& Value,
-    const sumOp<vector2D>& bop,
-    const int tag,
-    const label communicator
-)
-{
-    if (UPstream::warnComm != -1 && communicator != UPstream::warnComm)
-    {
-        Pout<< "** reducing:" << Value << " with comm:" << communicator
-            << " warnComm:" << UPstream::warnComm
-            << endl;
-        error::printStack(Pout);
-    }
-    allReduce(Value, 2, MPI_SCALAR, MPI_SUM, bop, tag, communicator);
-}
-
-
-void Foam::sumReduce
-(
-    scalar& Value,
-    label& Count,
-    const int tag,
-    const label communicator
-)
-{
-    if (UPstream::warnComm != -1 && communicator != UPstream::warnComm)
-    {
-        Pout<< "** sumReduce:" << Value << " with comm:" << communicator
-            << " warnComm:" << UPstream::warnComm
-            << endl;
-        error::printStack(Pout);
-    }
-    vector2D twoScalars(Value, scalar(Count));
-    reduce(twoScalars, sumOp<vector2D>(), tag, communicator);
-
-    Value = twoScalars.x();
-    Count = twoScalars.y();
-}
-
-
-void Foam::reduce
-(
-    scalar& Value,
-    const sumOp<scalar>& bop,
-    const int tag,
-    const label communicator,
-    label& requestID
-)
-{
-    iallReduce<scalar>(&Value, 1, MPI_SCALAR, MPI_SUM, communicator, requestID);
-}
-
-
-void Foam::reduce
-(
-    scalar values[],
-    const int size,
-    const sumOp<scalar>& bop,
-    const int tag,
-    const label communicator,
-    label& requestID
-)
-{
-    iallReduce<scalar>
-    (
-        values,
-        size,
-        MPI_SCALAR,
-        MPI_SUM,
-        communicator,
-        requestID
-    );
-}
-
-
-#if defined(WM_SPDP)
-void Foam::reduce
-(
-    solveScalar& Value,
-    const sumOp<solveScalar>& bop,
-    const int tag,
-    const label communicator
-)
-{
-    if (UPstream::warnComm != -1 && communicator != UPstream::warnComm)
-    {
-        Pout<< "** reducing:" << Value << " with comm:" << communicator
-            << " warnComm:" << UPstream::warnComm
-            << endl;
-        error::printStack(Pout);
-    }
-    allReduce(Value, 1, MPI_SOLVESCALAR, MPI_SUM, bop, tag, communicator);
-}
-
-
-void Foam::reduce
-(
-    solveScalar& Value,
-    const minOp<solveScalar>& bop,
-    const int tag,
-    const label communicator
-)
-{
-    if (UPstream::warnComm != -1 && communicator != UPstream::warnComm)
-    {
-        Pout<< "** reducing:" << Value << " with comm:" << communicator
-            << " warnComm:" << UPstream::warnComm
-            << endl;
-        error::printStack(Pout);
-    }
-    allReduce(Value, 1, MPI_SOLVESCALAR, MPI_MIN, bop, tag, communicator);
-}
-
-
-void Foam::reduce
-(
-    Vector2D<solveScalar>& Value,
-    const sumOp<Vector2D<solveScalar>>& bop,
-    const int tag,
-    const label communicator
-)
-{
-    if (UPstream::warnComm != -1 && communicator != UPstream::warnComm)
-    {
-        Pout<< "** reducing:" << Value << " with comm:" << communicator
-            << " warnComm:" << UPstream::warnComm
-            << endl;
-        error::printStack(Pout);
-    }
-    allReduce(Value, 2, MPI_SOLVESCALAR, MPI_SUM, bop, tag, communicator);
-}
-
-
-void Foam::sumReduce
-(
-    solveScalar& Value,
-    label& Count,
-    const int tag,
-    const label communicator
-)
-{
-    if (UPstream::warnComm != -1 && communicator != UPstream::warnComm)
-    {
-        Pout<< "** reducing:" << Value << " with comm:" << communicator
-            << " warnComm:" << UPstream::warnComm
-            << endl;
-        error::printStack(Pout);
-    }
-    Vector2D<solveScalar> twoScalars(Value, solveScalar(Count));
-    reduce(twoScalars, sumOp<Vector2D<solveScalar>>(), tag, communicator);
-
-    Value = twoScalars.x();
-    Count = twoScalars.y();
-}
-
-
-void Foam::reduce
-(
-    solveScalar& Value,
-    const sumOp<solveScalar>& bop,
-    const int tag,
-    const label communicator,
-    label& requestID
-)
-{
-    iallReduce<solveScalar>
-    (
-        &Value,
-        1,
-        MPI_SOLVESCALAR,
-        MPI_SUM,
-        communicator,
-        requestID
-    );
-}
-
-
-void Foam::reduce
-(
-    solveScalar values[],
-    const int size,
-    const sumOp<solveScalar>& bop,
-    const int tag,
-    const label communicator,
-    label& requestID
-)
-{
-    iallReduce<solveScalar>
-    (
-        values,
-        size,
-        MPI_SOLVESCALAR,
-        MPI_SUM,
-        communicator,
-        requestID
-    );
-}
-#endif
-
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
 void Foam::UPstream::allToAll
 (
@@ -1437,22 +1188,15 @@ int Foam::UPstream::allocateTag(const char* s)
 
     if (debug)
     {
-        //if (UPstream::lateBlocking > 0)
-        //{
-        //    string& poutp = Pout.prefix();
-        //    poutp[poutp.size()-2*(UPstream::lateBlocking+2)+tag] = 'X';
-        //    Perr.prefix() = Pout.prefix();
-        //}
-        Pout<< "UPstream::allocateTag " << s
-            << " : tag:" << tag
-            << endl;
+        Pout<< "UPstream::allocateTag "
+            << s << " : tag:" << tag << endl;
     }
 
     return tag;
 }
 
 
-int Foam::UPstream::allocateTag(const word& s)
+int Foam::UPstream::allocateTag(const std::string& s)
 {
     int tag;
     if (PstreamGlobals::freedTags_.size())
@@ -1466,15 +1210,8 @@ int Foam::UPstream::allocateTag(const word& s)
 
     if (debug)
     {
-        //if (UPstream::lateBlocking > 0)
-        //{
-        //    string& poutp = Pout.prefix();
-        //    poutp[poutp.size()-2*(UPstream::lateBlocking+2)+tag] = 'X';
-        //    Perr.prefix() = Pout.prefix();
-        //}
-        Pout<< "UPstream::allocateTag " << s
-            << " : tag:" << tag
-            << endl;
+        Pout<< "UPstream::allocateTag "
+            << s.c_str() << " : tag:" << tag << endl;
     }
 
     return tag;
@@ -1485,29 +1222,19 @@ void Foam::UPstream::freeTag(const char* s, const int tag)
 {
     if (debug)
     {
-        //if (UPstream::lateBlocking > 0)
-        //{
-        //    string& poutp = Pout.prefix();
-        //    poutp[poutp.size()-2*(UPstream::lateBlocking+2)+tag] = ' ';
-        //    Perr.prefix() = Pout.prefix();
-        //}
-        Pout<< "UPstream::freeTag " << s << " tag:" << tag << endl;
+        Pout<< "UPstream::freeTag "
+            << s << " tag:" << tag << endl;
     }
     PstreamGlobals::freedTags_.append(tag);
 }
 
 
-void Foam::UPstream::freeTag(const word& s, const int tag)
+void Foam::UPstream::freeTag(const std::string& s, const int tag)
 {
     if (debug)
     {
-        //if (UPstream::lateBlocking > 0)
-        //{
-        //    string& poutp = Pout.prefix();
-        //    poutp[poutp.size()-2*(UPstream::lateBlocking+2)+tag] = ' ';
-        //    Perr.prefix() = Pout.prefix();
-        //}
-        Pout<< "UPstream::freeTag " << s << " tag:" << tag << endl;
+        Pout<< "UPstream::freeTag "
+            << s.c_str() << " tag:" << tag << endl;
     }
     PstreamGlobals::freedTags_.append(tag);
 }
diff --git a/src/Pstream/mpi/UPstreamBroadcast.C b/src/Pstream/mpi/UPstreamBroadcast.C
new file mode 100644
index 0000000000..7678f136f5
--- /dev/null
+++ b/src/Pstream/mpi/UPstreamBroadcast.C
@@ -0,0 +1,93 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | www.openfoam.com
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+    Copyright (C) 2022 OpenCFD Ltd.
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM.
+
+    OpenFOAM is free software: you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+    for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
+
+\*---------------------------------------------------------------------------*/
+
+#include "UPstream.H"
+#include "PstreamGlobals.H"
+#include "profilingPstream.H"
+
+#include <mpi.h>
+
+// * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
+
+bool Foam::UPstream::broadcast
+(
+    char* buf,
+    const std::streamsize bufSize,
+    const label communicator,
+    const int rootProcNo
+)
+{
+    if (!UPstream::parRun() || UPstream::nProcs(communicator) < 2)
+    {
+        // Nothing to do - ignore
+        return true;
+    }
+
+    //Needed?  PstreamGlobals::checkCommunicator(communicator, rootProcNo);
+
+    if (debug)
+    {
+        Pout<< "UPstream::broadcast : root:" << rootProcNo
+            << " comm:" << communicator
+            << " size:" << label(bufSize)
+            << Foam::endl;
+    }
+    if (UPstream::warnComm != -1 && communicator != UPstream::warnComm)
+    {
+        Pout<< "UPstream::broadcast : root:" << rootProcNo
+            << " comm:" << communicator
+            << " size:" << label(bufSize)
+            << " warnComm:" << UPstream::warnComm
+            << Foam::endl;
+        error::printStack(Pout);
+    }
+
+    profilingPstream::beginTiming();
+
+    bool failed = MPI_Bcast
+    (
+        buf,
+        bufSize,
+        MPI_BYTE,
+        rootProcNo,
+        PstreamGlobals::MPICommunicators_[communicator]
+    );
+
+    if (rootProcNo == UPstream::myProcNo(communicator))
+    {
+        profilingPstream::addScatterTime();
+    }
+    else
+    {
+        profilingPstream::addGatherTime();
+    }
+
+    return !failed;
+}
+
+
+// ************************************************************************* //
diff --git a/src/Pstream/mpi/UPstreamReduce.C b/src/Pstream/mpi/UPstreamReduce.C
new file mode 100644
index 0000000000..4b112d3d92
--- /dev/null
+++ b/src/Pstream/mpi/UPstreamReduce.C
@@ -0,0 +1,211 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | www.openfoam.com
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+    Copyright (C) 2022 OpenCFD Ltd.
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM.
+
+    OpenFOAM is free software: you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+    for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
+
+\*---------------------------------------------------------------------------*/
+
+#include "Pstream.H"
+#include "PstreamReduceOps.H"
+#include "allReduce.H"
+
+#include <mpi.h>
+#include <cinttypes>
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+// Specialisations for bool
+
+void Foam::reduce
+(
+    bool& value,
+    const andOp<bool>&,
+    const int tag,
+    const label comm
+)
+{
+    // This can also work:
+    // PstreamDetail::allReduce(&value, 1, MPI_BYTE, MPI_BAND, tag, comm);
+    PstreamDetail::allReduce(&value, 1, MPI_C_BOOL, MPI_LAND, tag, comm);
+}
+
+
+void Foam::reduce
+(
+    bool& value,
+    const orOp<bool>&,
+    const int tag,
+    const label comm
+)
+{
+    // This can also work:
+    // PstreamDetail::allReduce(&value, 1, MPI_BYTE, MPI_BOR, tag, comm);
+    PstreamDetail::allReduce(&value, 1, MPI_C_BOOL, MPI_LOR, tag, comm);
+}
+
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+// Specialisations for common reduction types
+
+#undef  Pstream_CommonReductions
+#define Pstream_CommonReductions(Native, TaggedType)                          \
+                                                                              \
+void Foam::reduce                                                             \
+(                                                                             \
+    Native& value,                                                            \
+    const minOp<Native>&,                                                     \
+    const int tag,                                                            \
+    const label comm                                                          \
+)                                                                             \
+{                                                                             \
+    PstreamDetail::allReduce<Native>                                          \
+    (                                                                         \
+        &value, 1, TaggedType, MPI_MIN, tag, comm                             \
+    );                                                                        \
+}                                                                             \
+                                                                              \
+void Foam::reduce                                                             \
+(                                                                             \
+    Native& value,                                                            \
+    const maxOp<Native>&,                                                     \
+    const int tag,                                                            \
+    const label comm                                                          \
+)                                                                             \
+{                                                                             \
+    PstreamDetail::allReduce<Native>                                          \
+    (                                                                         \
+        &value, 1, TaggedType, MPI_MAX, tag, comm                             \
+    );                                                                        \
+}                                                                             \
+                                                                              \
+void Foam::reduce                                                             \
+(                                                                             \
+    Native& value,                                                            \
+    const sumOp<Native>&,                                                     \
+    const int tag,                                                            \
+    const label comm                                                          \
+)                                                                             \
+{                                                                             \
+    PstreamDetail::allReduce<Native>                                          \
+    (                                                                         \
+        &value, 1, TaggedType, MPI_SUM, tag, comm                             \
+    );                                                                        \
+}                                                                             \
+                                                                              \
+void Foam::reduce                                                             \
+(                                                                             \
+    Native values[],                                                          \
+    const int size,                                                           \
+    const sumOp<Native>&,                                                     \
+    const int tag,                                                            \
+    const label comm                                                          \
+)                                                                             \
+{                                                                             \
+    PstreamDetail::allReduce<Native>                                          \
+    (                                                                         \
+        values, size, TaggedType, MPI_SUM, tag, comm                          \
+    );                                                                        \
+}                                                                             \
+
+
+Pstream_CommonReductions(int32_t, MPI_INT32_T);
+Pstream_CommonReductions(int64_t, MPI_INT64_T);
+Pstream_CommonReductions(uint32_t, MPI_UINT32_T);
+Pstream_CommonReductions(uint64_t, MPI_UINT64_T);
+Pstream_CommonReductions(float,   MPI_FLOAT);
+Pstream_CommonReductions(double,  MPI_DOUBLE);
+
+#undef Pstream_CommonReductions
+
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+// Specialisations for floating-point types
+
+#undef  Pstream_FloatReductions
+#define Pstream_FloatReductions(Native, TaggedType)                           \
+                                                                              \
+void Foam::sumReduce                                                          \
+(                                                                             \
+    Native& value,                                                            \
+    label& count,                                                             \
+    const int tag,                                                            \
+    const label comm                                                          \
+)                                                                             \
+{                                                                             \
+    if (UPstream::parRun())                                                   \
+    {                                                                         \
+        Native values[2];                                                     \
+        values[0] = value;                                                    \
+        values[1] = static_cast<Native>(count);                               \
+                                                                              \
+        PstreamDetail::allReduce<Native>                                      \
+        (                                                                     \
+            values, 2, TaggedType, MPI_SUM, tag, comm                         \
+        );                                                                    \
+                                                                              \
+        value = values[0];                                                    \
+        count = static_cast<label>(values[1]);                                \
+    }                                                                         \
+}                                                                             \
+                                                                              \
+void Foam::reduce                                                             \
+(                                                                             \
+    Native& value,                                                            \
+    const sumOp<Native>&,                                                     \
+    const int tag,                                                            \
+    const label comm,                                                         \
+    label& requestID                                                          \
+)                                                                             \
+{                                                                             \
+    PstreamDetail::iallReduce<Native>                                         \
+    (                                                                         \
+        &value, 1, TaggedType, MPI_SUM, comm, requestID                       \
+    );                                                                        \
+}                                                                             \
+                                                                              \
+void Foam::reduce                                                             \
+(                                                                             \
+    Native values[],                                                          \
+    const int size,                                                           \
+    const sumOp<Native>&,                                                     \
+    const int tag,                                                            \
+    const label comm,                                                         \
+    label& requestID                                                          \
+)                                                                             \
+{                                                                             \
+    PstreamDetail::iallReduce<Native>                                         \
+    (                                                                         \
+        values, size, TaggedType, MPI_SUM, comm, requestID                    \
+    );                                                                        \
+}
+
+
+Pstream_FloatReductions(float, MPI_FLOAT);
+Pstream_FloatReductions(double, MPI_DOUBLE);
+
+#undef Pstream_FloatReductions
+
+
+// ************************************************************************* //
diff --git a/src/Pstream/mpi/allReduce.H b/src/Pstream/mpi/allReduce.H
index 5982bc2bec..d81666da02 100644
--- a/src/Pstream/mpi/allReduce.H
+++ b/src/Pstream/mpi/allReduce.H
@@ -6,6 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2012-2016 OpenFOAM Foundation
+    Copyright (C) 2022 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -23,37 +24,52 @@ License
     You should have received a copy of the GNU General Public License
     along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
 
-InNamespace
-    Foam
+Namespace
+    Foam::PstreamDetail
 
 Description
-    Various functions to wrap MPI_Allreduce
+    Some implementation details for Pstream and/or MPI.
+
+InNamespace
+    Foam::PstreamDetail
+
+Description
+    Functions to wrap MPI_Bcast, MPI_Allreduce, MPI_Iallreduce
 
 SourceFiles
     allReduceTemplates.C
 
 \*---------------------------------------------------------------------------*/
 
-#ifndef allReduce_H
-#define allReduce_H
+#ifndef Foam_allReduce_H
+#define Foam_allReduce_H
 
 #include "UPstream.H"
-
 #include <mpi.h>
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
 namespace Foam
 {
+namespace PstreamDetail
+{
 
-template<class Type, class BinaryOp>
+template<class Type>
+void allBroadcast
+(
+    Type* values,
+    int count,
+    MPI_Datatype datatype,
+    const label communicator
+);
+
+template<class Type>
 void allReduce
 (
-    Type& Value,
+    Type* values,
     int count,
-    MPI_Datatype MPIType,
-    MPI_Op op,
-    const BinaryOp& bop,
+    MPI_Datatype datatype,
+    MPI_Op optype,
     const int tag,
     const label communicator
 );
@@ -61,16 +77,17 @@ void allReduce
 template<class Type>
 void iallReduce
 (
-    void* Value,
+    Type* values,
     int count,
-    MPI_Datatype MPIType,
-    MPI_Op op,
+    MPI_Datatype datatype,
+    MPI_Op optype,
     const label communicator,
     label& requestID
 );
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
+} // End namespace PstreamDetail
 } // End namespace Foam
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
diff --git a/src/Pstream/mpi/allReduceTemplates.C b/src/Pstream/mpi/allReduceTemplates.C
index 2c8e928407..c052ab3b79 100644
--- a/src/Pstream/mpi/allReduceTemplates.C
+++ b/src/Pstream/mpi/allReduceTemplates.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2012-2015 OpenFOAM Foundation
-    Copyright (C) 2019-2020 OpenCFD Ltd.
+    Copyright (C) 2019-2022 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -28,18 +28,16 @@ License
 
 #include "allReduce.H"
 #include "profilingPstream.H"
+#include "PstreamGlobals.H"
 
 // * * * * * * * * * * * * * * * Global Functions  * * * * * * * * * * * * * //
 
-template<class Type, class BinaryOp>
-void Foam::allReduce
+template<class Type>
+void Foam::PstreamDetail::allBroadcast
 (
-    Type& Value,
-    int MPICount,
-    MPI_Datatype MPIType,
-    MPI_Op MPIOp,
-    const BinaryOp& bop,
-    const int tag,
+    Type* values,
+    int count,
+    MPI_Datatype datatype,
     const label communicator
 )
 {
@@ -50,129 +48,76 @@ void Foam::allReduce
 
     profilingPstream::beginTiming();
 
-    if (UPstream::nProcs(communicator) <= UPstream::nProcsSimpleSum)
+    // const int retval =
+    MPI_Bcast
+    (
+        values,
+        count,
+        datatype,
+        0,  // (root process) is master == UPstream::masterNo()
+        PstreamGlobals::MPICommunicators_[communicator]
+    );
+
+    profilingPstream::addScatterTime();
+}
+
+
+template<class Type>
+void Foam::PstreamDetail::allReduce
+(
+    Type* values,
+    int count,
+    MPI_Datatype datatype,
+    MPI_Op optype,
+    const int tag,
+    const label communicator
+)
+{
+    if (!UPstream::parRun())
     {
-        if (UPstream::master(communicator))
+        return;
+    }
+
+    if (UPstream::warnComm != -1 && communicator != UPstream::warnComm)
+    {
+        Pout<< "** reducing:";
+        if (count == 1)
         {
-            for (const int proci : UPstream::subProcs(communicator))
-            {
-                Type value;
-
-                if
-                (
-                    MPI_Recv
-                    (
-                        &value,
-                        MPICount,
-                        MPIType,
-                        proci,
-                        tag,
-                        PstreamGlobals::MPICommunicators_[communicator],
-                        MPI_STATUS_IGNORE
-                    )
-                )
-                {
-                    FatalErrorInFunction
-                        << "MPI_Recv failed"
-                        << Foam::abort(FatalError);
-                }
-
-                Value = bop(Value, value);
-            }
+            Pout<< (*values);
         }
         else
         {
-            if
-            (
-                MPI_Send
-                (
-                    &Value,
-                    MPICount,
-                    MPIType,
-                    UPstream::masterNo(),
-                    tag,
-                    PstreamGlobals::MPICommunicators_[communicator]
-                )
-            )
-            {
-                FatalErrorInFunction
-                    << "MPI_Send failed"
-                    << Foam::abort(FatalError);
-            }
-        }
-
-
-        if (UPstream::master(communicator))
-        {
-            for (const int proci : UPstream::subProcs(communicator))
-            {
-                if
-                (
-                    MPI_Send
-                    (
-                        &Value,
-                        MPICount,
-                        MPIType,
-                        proci,
-                        tag,
-                        PstreamGlobals::MPICommunicators_[communicator]
-                    )
-                )
-                {
-                    FatalErrorInFunction
-                        << "MPI_Send failed"
-                        << Foam::abort(FatalError);
-                }
-            }
-        }
-        else
-        {
-            if
-            (
-                MPI_Recv
-                (
-                    &Value,
-                    MPICount,
-                    MPIType,
-                    UPstream::masterNo(),
-                    tag,
-                    PstreamGlobals::MPICommunicators_[communicator],
-                    MPI_STATUS_IGNORE
-                )
-            )
-            {
-                FatalErrorInFunction
-                    << "MPI_Recv failed"
-                    << Foam::abort(FatalError);
-            }
+            Pout<< UList<Type>(values, count);
         }
+        Pout<< " with comm:" << communicator
+            << " warnComm:" << UPstream::warnComm << endl;
+        error::printStack(Pout);
     }
-    else
-    {
-        Type sum;
-        MPI_Allreduce
-        (
-            &Value,
-            &sum,
-            MPICount,
-            MPIType,
-            MPIOp,
-            PstreamGlobals::MPICommunicators_[communicator]
-        );
-        Value = sum;
-    }
+
+    profilingPstream::beginTiming();
+
+    // const int retval =
+    MPI_Allreduce
+    (
+        MPI_IN_PLACE,
+        values,
+        count,
+        datatype,
+        optype,
+        PstreamGlobals::MPICommunicators_[communicator]
+    );
 
     profilingPstream::addReduceTime();
 }
 
 
 template<class Type>
-void Foam::iallReduce
+void Foam::PstreamDetail::iallReduce
 (
-    void* recvBuf,
-    int MPICount,
-    MPI_Datatype MPIType,
-    MPI_Op MPIOp,
+    Type* values,
+    int count,
+    MPI_Datatype datatype,
+    MPI_Op optype,
     const label communicator,
     label& requestID
 )
@@ -184,9 +129,16 @@ void Foam::iallReduce
 
     if (UPstream::warnComm != -1 && communicator != UPstream::warnComm)
     {
-        Pout<< "** non-blocking reducing:"
-            << UList<Type>(static_cast<Type*>(recvBuf), MPICount)
-            << " with comm:" << communicator
+        Pout<< "** non-blocking reducing:";
+        if (count == 1)
+        {
+            Pout<< (*values);
+        }
+        else
+        {
+            Pout<< UList<Type>(values, count);
+        }
+        Pout<< " with comm:" << communicator
             << " warnComm:" << UPstream::warnComm << endl;
         error::printStack(Pout);
     }
@@ -200,10 +152,10 @@ void Foam::iallReduce
         MPI_Iallreduce
         (
             MPI_IN_PLACE,
-            recvBuf,
-            MPICount,
-            MPIType,
-            MPIOp,
+            values,
+            count,
+            datatype,
+            optype,
             PstreamGlobals::MPICommunicators_[communicator],
             &request
         )
@@ -211,7 +163,7 @@ void Foam::iallReduce
     {
         FatalErrorInFunction
             << "MPI_Iallreduce failed for "
-            << UList<Type>(static_cast<Type*>(recvBuf), MPICount)
+            << UList<Type>(values, count)
             << Foam::abort(FatalError);
     }
 
@@ -238,17 +190,17 @@ void Foam::iallReduce
         MPI_Allreduce
         (
             MPI_IN_PLACE,
-            recvBuf,
-            MPICount,
-            MPIType,
-            MPIOp,
+            values,
+            count,
+            datatype,
+            optype,
             PstreamGlobals::MPICommunicators_[communicator]
         )
     )
     {
         FatalErrorInFunction
             << "MPI_Allreduce failed for "
-            << UList<Type>(static_cast<Type*>(recvBuf), MPICount)
+            << UList<Type>(values, count)
             << Foam::abort(FatalError);
     }
     requestID = -1;
diff --git a/src/fvOptions/sources/derived/meanVelocityForce/patchMeanVelocityForce/patchMeanVelocityForce.C b/src/fvOptions/sources/derived/meanVelocityForce/patchMeanVelocityForce/patchMeanVelocityForce.C
index 8684878b4b..d2095839c2 100644
--- a/src/fvOptions/sources/derived/meanVelocityForce/patchMeanVelocityForce/patchMeanVelocityForce.C
+++ b/src/fvOptions/sources/derived/meanVelocityForce/patchMeanVelocityForce/patchMeanVelocityForce.C
@@ -6,6 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2015-2016 OpenFOAM Foundation
+    Copyright (C) 2022 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -71,15 +72,15 @@ Foam::scalar Foam::fv::patchMeanVelocityForce::magUbarAve
     const volVectorField& U
 ) const
 {
-    vector2D sumAmagUsumA
-    (
+    FixedList<scalar, 2> sumAmagUsumA(Zero);
+
+    sumAmagUsumA[0] +=
         sum
         (
             (flowDir_ & U.boundaryField()[patchi_])
-           *mesh_.boundary()[patchi_].magSf()
-        ),
-        sum(mesh_.boundary()[patchi_].magSf())
-    );
+          * mesh_.boundary()[patchi_].magSf()
+        );
+    sumAmagUsumA[1] += sum(mesh_.boundary()[patchi_].magSf());
 
 
     // If the mean velocity force is applied to a cyclic patch
@@ -89,29 +90,29 @@ Foam::scalar Foam::fv::patchMeanVelocityForce::magUbarAve
 
     if (Pstream::parRun() && isA<cyclicPolyPatch>(patches[patchi_]))
     {
-        labelList processorCyclicPatches
+        for
         (
-            processorCyclicPolyPatch::patchIDs(patch_, patches)
-        );
-
-        forAll(processorCyclicPatches, pcpi)
+            const label patchi
+          : processorCyclicPolyPatch::patchIDs(patch_, patches)
+        )
         {
-            const label patchi = processorCyclicPatches[pcpi];
-
-            sumAmagUsumA.x() +=
+            sumAmagUsumA[0] +=
                 sum
                 (
                     (flowDir_ & U.boundaryField()[patchi])
-                   *mesh_.boundary()[patchi].magSf()
+                  * mesh_.boundary()[patchi].magSf()
                 );
-
-            sumAmagUsumA.y() += sum(mesh_.boundary()[patchi].magSf());
+            sumAmagUsumA[1] += sum(mesh_.boundary()[patchi].magSf());
         }
     }
 
-    mesh_.reduce(sumAmagUsumA, sumOp<vector2D>());
+    mesh_.reduce(sumAmagUsumA, sumOp<scalar>());
 
-    return sumAmagUsumA.x()/sumAmagUsumA.y();
+    return
+    (
+        sumAmagUsumA[0]
+      / stabilise(sumAmagUsumA[1], VSMALL)
+    );
 }
 
 
diff --git a/src/lumpedPointMotion/state/lumpedPointState.C b/src/lumpedPointMotion/state/lumpedPointState.C
index 5dc1c5e434..f84f39e0b6 100644
--- a/src/lumpedPointMotion/state/lumpedPointState.C
+++ b/src/lumpedPointMotion/state/lumpedPointState.C
@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2016-2020 OpenCFD Ltd.
+    Copyright (C) 2016-2022 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -405,14 +405,8 @@ bool Foam::lumpedPointState::readData
     {
         // Scatter master data using communication scheme
 
-        const List<Pstream::commsStruct>& comms =
-        (
-            (Pstream::nProcs() < Pstream::nProcsSimpleSum)
-          ? Pstream::linearCommunication()
-          : Pstream::treeCommunication()
-        );
-
         // Get my communication order
+        const List<Pstream::commsStruct>& comms = Pstream::whichCommunication();
         const Pstream::commsStruct& myComm = comms[Pstream::myProcNo()];
 
         // Receive from up