From a01f3ed8b706dc58509eb12bda806a117abbe15e Mon Sep 17 00:00:00 2001
From: Mark Olesen <Mark.Olesen@esi-group.com>
Date: Mon, 17 Mar 2025 15:52:22 +0100
Subject: [PATCH] ENH: add node-based gatherList()
---
src/OpenFOAM/db/IOstreams/Pstreams/Pstream.H | 11 ++
.../IOstreams/Pstreams/PstreamGatherList.txx | 140 +++++++++++++++++-
2 files changed, 150 insertions(+), 1 deletion(-)
diff --git a/src/OpenFOAM/db/IOstreams/Pstreams/Pstream.H b/src/OpenFOAM/db/IOstreams/Pstreams/Pstream.H
index fb964d25e7c..28d70dbf3af 100644
--- a/src/OpenFOAM/db/IOstreams/Pstreams/Pstream.H
+++ b/src/OpenFOAM/db/IOstreams/Pstreams/Pstream.H
@@ -459,6 +459,17 @@ public:
const int communicator
);
+ //- Gather data, keeping individual values separate.
+ // \returns True if topo algorithm was applied
+ template<class T>
+ static bool gatherList_topo_algorithm
+ (
+ //! [in,out]
+ UList<T>& values,
+ const int tag,
+ const int communicator
+ );
+
//- Implementation: inverse of gatherList_algorithm
template<class T>
static void scatterList_algorithm
diff --git a/src/OpenFOAM/db/IOstreams/Pstreams/PstreamGatherList.txx b/src/OpenFOAM/db/IOstreams/Pstreams/PstreamGatherList.txx
index d850fe348e9..1e8c31a2170 100644
--- a/src/OpenFOAM/db/IOstreams/Pstreams/PstreamGatherList.txx
+++ b/src/OpenFOAM/db/IOstreams/Pstreams/PstreamGatherList.txx
@@ -252,6 +252,127 @@ void Foam::Pstream::gatherList_algorithm
}
+template<class T>
+bool Foam::Pstream::gatherList_topo_algorithm
+(
+ UList<T>& values,
+ const int tag,
+ const int communicator
+)
+{
+ const bool withTopo =
+ (
+ UPstream::is_parallel(communicator)
+ && UPstream::usingTopoControl(UPstream::topoControls::gatherList)
+ && UPstream::usingNodeComms(communicator)
+ );
+
+ if (withTopo)
+ {
+ // Topological gathering
+
+ if (FOAM_UNLIKELY(values.size() < UPstream::nProcs(communicator)))
+ {
+ FatalErrorInFunction
+ << "List of values:" << values.size()
+ << " < numProcs:" << UPstream::nProcs(communicator) << nl
+ << Foam::abort(FatalError);
+ }
+
+ // Overall node-wise offsets
+ const auto& off = UPstream::interNode_offsets();
+
+ // The per-node processor range
+ const auto& nodeProcs = UPstream::localNode_parentProcs();
+
+ // The per-node sub-section of values
+ auto nodeValues = values.slice(nodeProcs.start(), nodeProcs.size());
+
+ // Stage 1: gather values within a node
+ // - linear for local-node (assume communication is fast)
+
+ if (UPstream::is_parallel(UPstream::commLocalNode()))
+ {
+ const auto subComm = UPstream::commLocalNode();
+ constexpr bool linear(true);
+
+ Pstream::gatherList_algorithm<T>
+ (
+ UPstream::whichCommunication(subComm, linear),
+ nodeValues,
+ tag,
+ subComm
+ );
+ }
+
+ // Stage 2: gather between node leaders
+ // - this unfortunately corresponds to a gatherv process
+ // (number of cores per node is not identical)
+ // - code strongly resembles globalIndex::gather
+
+ if (UPstream::is_parallel(UPstream::commInterNode()))
+ {
+ const auto subComm = UPstream::commInterNode();
+
+ if (UPstream::master(subComm))
+ {
+ for (const int proci : UPstream::subProcs(subComm))
+ {
+ auto slot =
+ values.slice(off[proci], off[proci+1]-off[proci]);
+
+ // Probably not contiguous though,
+ // otherwise would have used mpiGather()
+
+ if constexpr (is_contiguous_v<T>)
+ {
+ UIPstream::read
+ (
+ UPstream::commsTypes::scheduled,
+ proci,
+ slot,
+ tag,
+ subComm
+ );
+ }
+ else
+ {
+ IPstream::recv(slot, proci, tag, subComm);
+ }
+ }
+ }
+ else
+ {
+ if constexpr (is_contiguous_v<T>)
+ {
+ UOPstream::write
+ (
+ UPstream::commsTypes::scheduled,
+ UPstream::masterNo(),
+ nodeValues,
+ tag,
+ subComm
+ );
+ }
+ else
+ {
+ OPstream::send
+ (
+ nodeValues,
+ UPstream::commsTypes::scheduled,
+ UPstream::masterNo(),
+ tag,
+ subComm
+ );
+ }
+ }
+ }
+ }
+
+ return withTopo;
+}
+
+
template<class T>
void Foam::Pstream::scatterList_algorithm
(
@@ -448,7 +569,15 @@ void Foam::Pstream::gatherList
auto* ptr = values.data() + UPstream::myProcNo(communicator);
UPstream::mpiGather(ptr, ptr, 1, communicator);
}
- else
+ else if
+ (
+ !Pstream::gatherList_topo_algorithm
+ (
+ values,
+ tag,
+ communicator
+ )
+ )
{
// Communication order
const auto& commOrder = UPstream::whichCommunication(communicator);
@@ -486,6 +615,15 @@ void Foam::Pstream::allGatherList
}
else
{
+ // IMPORTANT: always call the *_algorithm() versions here and
+ // never the base versions [eg, Pstream::gatherList()] since
+ // the communcation order must be absolutely identical
+ // for the gatherList and scatterList, otherwise the results will
+ // not replicate the allGather behaviour.
+ //
+ // This also means that we must avoid the gatherList_topo_algorithm()
+ // as well, since this does not pair well with scatterList_algorithm()
+
// Communication order
const auto& commOrder = UPstream::whichCommunication(communicator);
--
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