From: David Wells Date: Tue, 13 Aug 2024 02:13:39 +0000 (-0600) Subject: PETScWrappers::MatrixBase: use small_vector to avoid an allocation. X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=refs%2Fpull%2F17507%2Fhead;p=dealii.git PETScWrappers::MatrixBase: use small_vector to avoid an allocation. Make it big enough to support a common Stokes element. --- diff --git a/include/deal.II/lac/petsc_matrix_base.h b/include/deal.II/lac/petsc_matrix_base.h index 8dea3097ab..6c7d866ab6 100644 --- a/include/deal.II/lac/petsc_matrix_base.h +++ b/include/deal.II/lac/petsc_matrix_base.h @@ -28,10 +28,13 @@ # include # include +# include + # include # include # include +# include # include DEAL_II_NAMESPACE_OPEN @@ -1443,27 +1446,36 @@ namespace PETScWrappers const auto petsc_row = static_cast(row); AssertIntegerConversion(petsc_row, row); - std::vector column_indices; - column_indices.reserve(n_cols); - std::vector column_values; - column_values.reserve(n_cols); + // Use 100 entries so that we can store a row of a matrix constructed with + // FESystem<3>(FE_Q<3>(2), 3, FE_Q<3>(1), 1) (i.e., a common Stokes FE, + // which has 89 DoFs) with room to spare without allocating memory in the + // free store. + // + // Setting up small_vectors isn't free so only set up column_values if we + // actually use it. + boost::container::small_vector column_indices; + std::optional> + column_values; + + const PetscScalar *values_ptr = nullptr; if (elide_zero_values == false) { column_indices.resize(n_cols); - column_values.resize(n_cols); for (size_type j = 0; j < n_cols; ++j) { AssertIsFinite(values[j]); column_indices[j] = static_cast(col_indices[j]); AssertIntegerConversion(column_indices[j], col_indices[j]); - column_values[j] = values[j]; } + + values_ptr = values; } else { // Otherwise, extract nonzero values in each row and get the // respective index. + column_values.emplace(); for (size_type j = 0; j < n_cols; ++j) { const PetscScalar value = values[j]; @@ -1472,9 +1484,10 @@ namespace PETScWrappers { column_indices.push_back(static_cast(col_indices[j])); AssertIntegerConversion(column_indices.back(), col_indices[j]); - column_values.push_back(value); + column_values->push_back(value); } } + values_ptr = column_values->data(); } const auto petsc_n_columns = static_cast(column_indices.size()); @@ -1489,7 +1502,7 @@ namespace PETScWrappers &petsc_row, petsc_n_columns, column_indices.data(), - column_values.data(), + values_ptr, operation == VectorOperation::insert ? INSERT_VALUES : ADD_VALUES); AssertThrow(ierr == 0, ExcPETScError(ierr));