From cd63cc83c2c88560d25d245195f1b4a70a0e3296 Mon Sep 17 00:00:00 2001
From: Razvan Nane <razvan.nane@bigdataccelerate.com>
Date: Thu, 26 Oct 2023 06:40:06 +0200
Subject: [PATCH] Remove redundant cpu decomposition when using gpu

---
 opm/simulators/linalg/ISTLSolverEbos.hpp    | 21 ++++++++++++++-------
 opm/simulators/linalg/ISTLSolverEbosBda.hpp | 10 +++++++++-
 2 files changed, 23 insertions(+), 8 deletions(-)

diff --git a/opm/simulators/linalg/ISTLSolverEbos.hpp b/opm/simulators/linalg/ISTLSolverEbos.hpp
index 59fdb3871..de72f0431 100644
--- a/opm/simulators/linalg/ISTLSolverEbos.hpp
+++ b/opm/simulators/linalg/ISTLSolverEbos.hpp
@@ -306,14 +306,8 @@ std::unique_ptr<Matrix> blockJacobiAdjacency(const Grid& grid,
             return flexibleSolver_.size();
         }
 
-        void prepare(const SparseMatrixAdapter& M, Vector& b)
+        void initPrepare(const Matrix& M, Vector& b)
         {
-            prepare(M.istlMatrix(), b);
-        }
-
-        void prepare(const Matrix& M, Vector& b)
-        {
-            OPM_TIMEBLOCK(istlSolverEbosPrepare);
             const bool firstcall = (matrix_ == nullptr);
 #if HAVE_MPI
             if (firstcall && isParallel()) {
@@ -344,6 +338,19 @@ std::unique_ptr<Matrix> blockJacobiAdjacency(const Grid& grid,
             if (isParallel() && prm_[activeSolverNum_].template get<std::string>("preconditioner.type") != "ParOverILU0") {
                 detail::makeOverlapRowsInvalid(getMatrix(), overlapRows_);
             }
+        }
+
+        void prepare(const SparseMatrixAdapter& M, Vector& b)
+        {
+            prepare(M.istlMatrix(), b);
+        }
+
+        void prepare(const Matrix& M, Vector& b)
+        {
+            OPM_TIMEBLOCK(istlSolverEbosPrepare);
+
+            initPrepare(M,b);
+
             prepareFlexibleSolver();
         }
 
diff --git a/opm/simulators/linalg/ISTLSolverEbosBda.hpp b/opm/simulators/linalg/ISTLSolverEbosBda.hpp
index 6eaff0218..1f086eb7a 100644
--- a/opm/simulators/linalg/ISTLSolverEbosBda.hpp
+++ b/opm/simulators/linalg/ISTLSolverEbosBda.hpp
@@ -182,7 +182,15 @@ public:
     {
         OPM_TIMEBLOCK(prepare);
         [[maybe_unused]] const bool firstcall = (this->matrix_ == nullptr);
-        ParentType::prepare(M,b);
+
+        // Avoid performing the decomposition on CPU when we also do it on GPU, but we do
+        // need to initialize the pointers.
+         if(bdaBridge_){
+            ParentType::initPrepare(M,b);
+         }
+         else {
+             ParentType::prepare(M,b);
+         }
 
 #if HAVE_OPENCL
         // update matrix entries for solvers.