From e59235be1bc72e8dd4816a14e896d517bf59ee47 Mon Sep 17 00:00:00 2001
From: Gilles Grospellier <Gilles.Grospellier@cea.fr>
Date: Wed, 18 Feb 2026 15:17:06 +0100
Subject: [PATCH] [femutils] Use accelerator API in
 'CsrFormat::translateToLinearSystem()'.

This will prevent some memory roundtrip between CPU and GPU.
---
 femutils/CMakeLists.txt     |  2 +-
 femutils/CsrFormatMatrix.cc | 44 +++++++++++++++++++++++++++----------
 2 files changed, 34 insertions(+), 12 deletions(-)

diff --git a/femutils/CMakeLists.txt b/femutils/CMakeLists.txt
index 88081665..dd2f4a69 100644
--- a/femutils/CMakeLists.txt
+++ b/femutils/CMakeLists.txt
@@ -3,6 +3,7 @@ option(ENABLE_DEBUG_MATRIX "Enable Debug matrix instead of a sparse one" OFF)
 set(ACCELERATOR_SOURCES
   ArcaneFemFunctionsGpu.cc
   CsrDoFLinearSystemImpl.cc
+  CsrFormatMatrix.cc
   BSRFormat.cc
 )
 
@@ -27,7 +28,6 @@ add_library(FemUtils
   DoFLinearSystem.cc
   CooFormatMatrix.h
   CsrFormatMatrix.h
-  CsrFormatMatrix.cc
   CsrFormatMatrixView.h
   CsrFormatMatrixView.cc
   BSRFormat.h
diff --git a/femutils/CsrFormatMatrix.cc b/femutils/CsrFormatMatrix.cc
index 2e3c9eb2..18707868 100644
--- a/femutils/CsrFormatMatrix.cc
+++ b/femutils/CsrFormatMatrix.cc
@@ -17,6 +17,8 @@
 #include <arcane/core/IItemFamily.h>
 
 #include <arcane/accelerator/core/RunQueue.h>
+#include <arcane/accelerator/NumArrayViews.h>
+#include <arcane/accelerator/RunCommandLoop.h>
 
 #include "CsrFormatMatrix.h"
 #include "DoFLinearSystem.h"
@@ -58,27 +60,45 @@ initialize(IItemFamily* dof_family, Int32 nnz, Int32 nbRow, RunQueue& queue)
 void CsrFormat::
 translateToLinearSystem(DoFLinearSystem& linear_system, const RunQueue& queue)
 {
-  info() << "TranslateToLinearSystem this=" << this;
   bool do_set_csr = linear_system.hasSetCSRValues();
+  info() << "TranslateToLinearSystem this=" << this << " is_csr=" << do_set_csr;
+
+  const Int32 nb_row = m_matrix_row.dim1Size();
+  const Int32 matrix_column_size = m_matrix_column.dim1Size();
+
   // When using CSR format, we need to know the number of non zero values for
   // each row.
   // NOTE: it should be possible to compute that in setCoordinates().
   // and this value is constant if the structure of the matrix do not change
   // so we can store these values instead of recomputing them.
   if (do_set_csr) {
-    m_matrix_rows_nb_column.resize(m_matrix_row.extent0());
-    //m_matrix_rows_nb_column.fill(0);
+    m_matrix_rows_nb_column.resize(nb_row);
+    auto command = makeCommand(queue);
+    auto out_matrix_rows_nb_column = viewOut(command, m_matrix_rows_nb_column);
+    auto in_matrix_rows = viewIn(command, m_matrix_row);
+    command << RUNCOMMAND_LOOP1(iter, nb_row)
+    {
+      auto [i] = iter();
+      Int32 nb_column = 0;
+      if (((i + 1) < nb_row) && (in_matrix_rows(i) == in_matrix_rows(i + 1))) {
+        out_matrix_rows_nb_column[0];
+        return;
+      }
+      for (Int32 j = in_matrix_rows(i); ((i + 1) < nb_row && j < in_matrix_rows(i + 1)) || ((i + 1) == nb_row && j < matrix_column_size); j++) {
+        ++nb_column;
+      }
+      out_matrix_rows_nb_column[i] = nb_column;
+    };
+    CSRFormatView csr_view(view());
+    linear_system.setCSRValues(csr_view);
+    return;
   }
-  Int32 nb_row = m_matrix_row.dim1Size();
+
   for (Int32 i = 0; i < nb_row; i++) {
     m_matrix_rows_nb_column[i] = 0;
     if (((i + 1) < nb_row) && (m_matrix_row(i) == m_matrix_row(i + 1)))
       continue;
-    for (Int32 j = m_matrix_row(i); ((i + 1) < nb_row && j < m_matrix_row(i + 1)) || ((i + 1) == nb_row && j < m_matrix_column.dim1Size()); j++) {
-      if (do_set_csr) {
-        ++m_matrix_rows_nb_column[i];
-        continue;
-      }
+    for (Int32 j = m_matrix_row(i); ((i + 1) < nb_row && j < m_matrix_row(i + 1)) || ((i + 1) == nb_row && j < matrix_column_size); j++) {
       if (DoFLocalId(m_matrix_column(j)).isNull())
         continue;
       //info() << "Add: (" << i << ", " << m_matrix_column(j) << " v=" << m_matrix_value(j);
@@ -87,10 +107,12 @@ translateToLinearSystem(DoFLinearSystem& linear_system, const RunQueue& queue)
   }
 
   if (do_set_csr) {
-    CSRFormatView csr_view(view());
-    linear_system.setCSRValues(csr_view);
   }
 }
+
+/*---------------------------------------------------------------------------*/
+/*---------------------------------------------------------------------------*/
+
 CsrFormatMatrixView CsrFormat::
 view()
 {