Merge pull request #2942 from AlexandreSinger/feature-ap-partial-legalizer

[AP][GlobalPlacement] Improved Partial Legalizer Legality

Author: AlexandreSinger

vpr/src/analytical_place/analytical_solver.cpp

@@ -236,41 +236,17 @@ void QPHybridSolver::init_linear_system() {
     A_sparse.setFromTriplets(tripletList.begin(), tripletList.end());
 }
 
-/**
- * @brief Helper method to update the linear system with anchors to the current
- *        partial placement.
- *
- * For each moveable block (with row = i) in the netlist:
- *      A[i][i] = A[i][i] + coeff_pseudo_anchor;
- *      b[i] = b[i] + pos[block(i)] * coeff_pseudo_anchor;
- * Where coeff_pseudo_anchor grows with each iteration.
- *
- * This is basically a fast way of adding a connection between all moveable
- * blocks in the netlist and their target fixed placement location.
- *
- * See add_connection_to_system.
- *
- *  @param A_sparse_diff    The ceofficient matrix to update.
- *  @param b_x_diff         The x-dimension constant vector to update.
- *  @param b_y_diff         The y-dimension constant vector to update.
- *  @param p_placement      The location the moveable blocks should be anchored
- *                          to.
- *  @param num_moveable_blocks  The number of moveable blocks in the netlist.
- *  @param row_id_to_blk_id     Lookup for the row id from the APBlock Id.
- *  @param iteration        The current iteration of the Global Placer.
- */
-static inline void update_linear_system_with_anchors(Eigen::SparseMatrix<double>& A_sparse_diff,
-                                                     Eigen::VectorXd& b_x_diff,
-                                                     Eigen::VectorXd& b_y_diff,
-                                                     PartialPlacement& p_placement,
-                                                     size_t num_moveable_blocks,
-                                                     vtr::vector<APRowId, APBlockId> row_id_to_blk_id,
-                                                     unsigned iteration) {
+void QPHybridSolver::update_linear_system_with_anchors(
+    Eigen::SparseMatrix<double>& A_sparse_diff,
+    Eigen::VectorXd& b_x_diff,
+    Eigen::VectorXd& b_y_diff,
+    PartialPlacement& p_placement,
+    unsigned iteration) {
     // Anchor weights grow exponentially with iteration.
-    double coeff_pseudo_anchor = 0.01 * std::exp((double)iteration / 5);
-    for (size_t row_id_idx = 0; row_id_idx < num_moveable_blocks; row_id_idx++) {
+    double coeff_pseudo_anchor = anchor_weight_mult_ * std::exp((double)iteration / anchor_weight_exp_fac_);
+    for (size_t row_id_idx = 0; row_id_idx < num_moveable_blocks_; row_id_idx++) {
         APRowId row_id = APRowId(row_id_idx);
-        APBlockId blk_id = row_id_to_blk_id[row_id];
+        APBlockId blk_id = row_id_to_blk_id_[row_id];
         double pseudo_w = coeff_pseudo_anchor;
         A_sparse_diff.coeffRef(row_id_idx, row_id_idx) += pseudo_w;
         b_x_diff(row_id_idx) += pseudo_w * p_placement.block_x_locs[blk_id];
@@ -289,8 +265,7 @@ void QPHybridSolver::solve(unsigned iteration, PartialPlacement& p_placement) {
     //                         anchor-points (fixed block positions).
     if (iteration != 0) {
         update_linear_system_with_anchors(A_sparse_diff, b_x_diff, b_y_diff,
-                                          p_placement, num_moveable_blocks_,
-                                          row_id_to_blk_id_, iteration);
+                                          p_placement, iteration);
     }
     // Verify that the constant vectors are valid.
     VTR_ASSERT_DEBUG(!b_x_diff.hasNaN() && "b_x has NaN!");

vpr/src/analytical_place/analytical_solver.h

@@ -155,6 +155,21 @@ class QPHybridSolver : public AnalyticalSolver {
     /// sparse.
     static constexpr size_t star_num_pins_threshold = 3;
 
+    // The following constants are used to configure the anchor weighting.
+    // The weights of anchors grow exponentially each iteration by the following
+    // function:
+    //      anchor_w = anchor_weight_mult_ * e^(iter / anchor_weight_exp_fac_)
+    // The numbers below were empircally found to work well.
+
+    /// @brief Multiplier for the anchorweight. The smaller this number is, the
+    ///        weaker the anchors will be at the start.
+    static constexpr double anchor_weight_mult_ = 0.001;
+
+    /// @brief Factor for controlling the growth of the exponential term in the
+    ///        weight factor function. Larger numbers will cause the anchor
+    ///        weights to grow slower.
+    static constexpr double anchor_weight_exp_fac_ = 5.0;
+
     /**
      * @brief Initializes the linear system of Ax = b_x and Ay = b_y based on
      *        the APNetlist and the fixed APBlock locations.
@@ -165,6 +180,35 @@ class QPHybridSolver : public AnalyticalSolver {
      */
     void init_linear_system();
 
+    /**
+     * @brief Helper method to update the linear system with anchors to the
+     *        current partial placement.
+     *
+     * For each moveable block (with row = i) in the netlist:
+     *      A[i][i] = A[i][i] + coeff_pseudo_anchor;
+     *      b[i] = b[i] + pos[block(i)] * coeff_pseudo_anchor;
+     * Where coeff_pseudo_anchor grows with each iteration.
+     *
+     * This is basically a fast way of adding a connection between all moveable
+     * blocks in the netlist and their target fixed placement location.
+     *
+     * See add_connection_to_system.
+     *
+     *  @param A_sparse_diff    The ceofficient matrix to update.
+     *  @param b_x_diff         The x-dimension constant vector to update.
+     *  @param b_y_diff         The y-dimension constant vector to update.
+     *  @param p_placement      The location the moveable blocks should be
+     *                          anchored to.
+     *  @param num_moveable_blocks  The number of moveable blocks in the netlist.
+     *  @param row_id_to_blk_id     Lookup for the row id from the APBlock Id.
+     *  @param iteration        The current iteration of the Global Placer.
+     */
+    void update_linear_system_with_anchors(Eigen::SparseMatrix<double>& A_sparse_diff,
+                                           Eigen::VectorXd& b_x_diff,
+                                           Eigen::VectorXd& b_y_diff,
+                                           PartialPlacement& p_placement,
+                                           unsigned iteration);
+
     // The following variables represent the linear system without any anchor
     // points. These are filled in the constructor and never modified.
     // When the anchor-points are taken into consideration, the diagonal of the

vpr/src/analytical_place/flat_placement_bins.h

@@ -111,7 +111,6 @@ class FlatPlacementBins {
     inline const vtr::Rect<double>& bin_region(FlatPlacementBinId bin_id) const {
         VTR_ASSERT(bin_id.is_valid());
         return bin_region_[bin_id];
-        ;
     }
 
     /**

vpr/src/analytical_place/flat_placement_density_manager.cpp

@@ -80,6 +80,7 @@ FlatPlacementDensityManager::FlatPlacementDensityManager(const APNetlist& ap_net
                 auto tile_type = device_grid.get_physical_type(tile_loc);
                 int tw = tile_type->width;
                 int th = tile_type->height;
+                VTR_ASSERT_SAFE(tw != 0 && th != 0);
                 vtr::Rect<double> new_bin_region(vtr::Point<double>(x, y),
                                                  vtr::Point<double>(x + tw,
                                                                     y + th));
@@ -162,6 +163,10 @@ void FlatPlacementDensityManager::remove_block_from_bin(APBlockId blk_id,
 }
 
 void FlatPlacementDensityManager::import_placement_into_bins(const PartialPlacement& p_placement) {
+    // Empty the bins such that all blocks are no longer within the bins.
+    empty_bins();
+
+    // Insert each block in the netlist into their bin based on their placement.
     // TODO: Maybe import the fixed block locations in the constructor and then
     //       only import the moveable block locations.
     for (APBlockId blk_id : ap_netlist_.blocks()) {
@@ -215,9 +220,9 @@ void FlatPlacementDensityManager::empty_bins() {
     // Reset all of the bins and their utilizations.
     for (FlatPlacementBinId bin_id : bins_.bins()) {
         bins_.remove_all_blocks_from_bin(bin_id);
-        bin_utilization_[bin_id] = PrimitiveVector();
-        bin_overfill_[bin_id] = calc_bin_overfill(bin_utilization_[bin_id], bin_capacity_[bin_id]);
-        bin_underfill_[bin_id] = calc_bin_underfill(bin_utilization_[bin_id], bin_capacity_[bin_id]);
+        bin_utilization_[bin_id].clear();
+        bin_overfill_[bin_id].clear();
+        bin_underfill_[bin_id] = bin_capacity_[bin_id];
     }
     // Once all the bins are reset, all bins should be empty; therefore no bins
     // are overfilled.

vpr/src/analytical_place/flat_placement_density_manager.h

@@ -185,6 +185,9 @@ class FlatPlacementDensityManager {
      * @brief Import the given flat placement into the bins.
      *
      * This will place AP blocks into the bins that they are placed over.
+     *
+     * This will reset the bins before importing the placement. Anything inside
+     * the bins will be removed.
      */
     void import_placement_into_bins(const PartialPlacement& p_placement);
 

vpr/src/analytical_place/flat_placement_mass_calculator.cpp

@@ -234,6 +234,7 @@ static void print_capacities(const std::vector<PrimitiveVector>& logical_block_t
         VTR_LOG("\n");
     }
     VTR_LOG("\n");
+    // TODO: Print the masses of each model.
 }
 
 FlatPlacementMassCalculator::FlatPlacementMassCalculator(const APNetlist& ap_netlist,

vpr/src/analytical_place/global_placer.cpp

@@ -13,12 +13,16 @@
 #include "analytical_solver.h"
 #include "ap_flow_enums.h"
 #include "ap_netlist.h"
+#include "ap_netlist_fwd.h"
 #include "atom_netlist.h"
 #include "device_grid.h"
+#include "flat_placement_bins.h"
 #include "flat_placement_density_manager.h"
+#include "globals.h"
 #include "partial_legalizer.h"
 #include "partial_placement.h"
 #include "physical_types.h"
+#include "primitive_vector.h"
 #include "vpr_error.h"
 #include "vtr_log.h"
 #include "vtr_time.h"
@@ -90,9 +94,74 @@ SimPLGlobalPlacer::SimPLGlobalPlacer(e_partial_legalizer partial_legalizer_type,
     partial_legalizer_ = make_partial_legalizer(partial_legalizer_type,
                                                 ap_netlist_,
                                                 density_manager_,
+                                                prepacker,
                                                 log_verbosity_);
 }
 
+/**
+ * @brief Helper method to print the statistics on the given partial placement.
+ */
+static void print_placement_stats(const PartialPlacement& p_placement,
+                                  const APNetlist& ap_netlist,
+                                  FlatPlacementDensityManager& density_manager) {
+    // Print the placement HPWL
+    VTR_LOG("\tPlacement HPWL: %f\n", p_placement.get_hpwl(ap_netlist));
+
+    // Print density information. Need to reset the density manager to ensure
+    // the data is valid.
+    density_manager.import_placement_into_bins(p_placement);
+
+    // Print the number of overfilled bins.
+    size_t num_overfilled_bins = density_manager.get_overfilled_bins().size();
+    VTR_LOG("\tNumber of overfilled bins: %zu\n", num_overfilled_bins);
+
+    // Print the average overfill
+    float total_overfill = 0.0f;
+    for (FlatPlacementBinId bin_id : density_manager.get_overfilled_bins()) {
+        total_overfill += density_manager.get_bin_overfill(bin_id).manhattan_norm();
+    }
+    float avg_overfill = 0.0f;
+    if (num_overfilled_bins != 0)
+        avg_overfill = total_overfill / static_cast<float>(num_overfilled_bins);
+    VTR_LOG("\tAverage overfill magnitude: %f\n", avg_overfill);
+
+    // Print the number of overfilled tiles per type.
+    const auto& physical_tile_types = g_vpr_ctx.device().physical_tile_types;
+    const auto& device_grid = g_vpr_ctx.device().grid;
+    std::vector<unsigned> overfilled_tiles_by_type(physical_tile_types.size(), 0);
+    for (FlatPlacementBinId bin_id : density_manager.get_overfilled_bins()) {
+        const auto& bin_region = density_manager.flat_placement_bins().bin_region(bin_id);
+        auto tile_loc = t_physical_tile_loc((int)bin_region.xmin(),
+                                            (int)bin_region.ymin(),
+                                            0);
+        auto tile_type = device_grid.get_physical_type(tile_loc);
+        overfilled_tiles_by_type[tile_type->index]++;
+    }
+    VTR_LOG("\tOverfilled bins by tile type:\n");
+    for (size_t type_idx = 0; type_idx < physical_tile_types.size(); type_idx++) {
+        VTR_LOG("\t\t%10s: %zu\n",
+                physical_tile_types[type_idx].name.c_str(),
+                overfilled_tiles_by_type[type_idx]);
+    }
+
+    // Count the number of blocks that were placed in a bin which they cannot
+    // physically be placed into (according to their mass).
+    unsigned num_misplaced_blocks = 0;
+    for (FlatPlacementBinId bin_id : density_manager.get_overfilled_bins()) {
+        for (APBlockId ap_blk_id : density_manager.flat_placement_bins().bin_contained_blocks(bin_id)) {
+            // Get the blk mass and project it onto the capacity of its bin.
+            PrimitiveVector blk_mass = density_manager.mass_calculator().get_block_mass(ap_blk_id);
+            PrimitiveVector projected_mass = blk_mass;
+            projected_mass.project(density_manager.get_bin_capacity(bin_id));
+            // If the projected mass does not match its match, this implies that
+            // there this block does not belong in this bin.
+            if (projected_mass != blk_mass)
+                num_misplaced_blocks++;
+        }
+    }
+    VTR_LOG("\tNumber of blocks in an incompatible bin: %zu\n", num_misplaced_blocks);
+}
+
 /**
  * @brief Helper method to print the header of the per-iteration status updates
  *        of the global placer.
@@ -177,6 +246,13 @@ PartialPlacement SimPLGlobalPlacer::place() {
         if (hpwl_relative_gap < target_hpwl_relative_gap_)
             break;
     }
+
+    // Print some statistics on the final placement.
+    VTR_LOG("Placement after Global Placement:\n");
+    print_placement_stats(p_placement,
+                          ap_netlist_,
+                          *density_manager_);
+
     // Return the placement from the final iteration.
     // TODO: investigate saving the best solution found so far. It should be
     //       cheap to save a copy of the PartialPlacement object.

vpr/src/analytical_place/global_placer.h

@@ -116,7 +116,8 @@ class SimPLGlobalPlacer : public GlobalPlacer {
     ///        lower-bound placements. The placer will stop if the difference
     ///        between the two bounds, normalized to the upper-bound, is smaller
     ///        than this number.
-    static constexpr double target_hpwl_relative_gap_ = 0.10;
+    ///        This number was empircally found to work well.
+    static constexpr double target_hpwl_relative_gap_ = 0.05;
 
     /// @brief The solver which generates the lower-bound placement.
     std::unique_ptr<AnalyticalSolver> solver_;