Commented LookaheadProfiler

Author: Nathan Shreve

vpr/src/route/lookahead_profiler.cpp

@@ -3,23 +3,14 @@
 //
 
 #include <sstream>
-#include "lookahead_profiler.h"
-#include "vtr_error.h"
-#include "vtr_log.h"
+
 #include "globals.h"
+#include "lookahead_profiler.h"
+#include "re_cluster_util.h"
 #include "router_lookahead_map_utils.h"
 #include "vpr_utils.h"
-#include "re_cluster_util.h"
-
-LookaheadProfiler::LookaheadProfiler()
-    : is_empty(true) {
-    lookahead_verifier_csv.open("lookahead_verifier_info.csv", std::ios::out);
-
-    if (!lookahead_verifier_csv.is_open()) {
-        VTR_LOG_WARN("Could not open lookahead_verifier_info.csv");
-        return;
-    }
-}
+#include "vtr_error.h"
+#include "vtr_log.h"
 
 void LookaheadProfiler::record(int iteration,
                                int target_net_pin_index,
@@ -32,10 +23,14 @@ void LookaheadProfiler::record(int iteration,
     const auto& rr_graph = device_ctx.rr_graph;
     auto& route_ctx = g_vpr_ctx.routing();
 
-    if (!lookahead_verifier_csv.is_open())
-        return;
-
+    // If csv file hasn't been opened, open it and write out column headers
     if (is_empty) {
+        lookahead_verifier_csv.open("lookahead_verifier_info.csv", std::ios::out);
+
+        if (!lookahead_verifier_csv.is_open()) {
+            VTR_LOG_ERROR("Could not open lookahead_verifier_info.csv", "error");
+        }
+
         lookahead_verifier_csv
             << "iteration no."
             << ",source node"
@@ -63,72 +58,96 @@ void LookaheadProfiler::record(int iteration,
         is_empty = false;
     }
 
+    if (!lookahead_verifier_csv.is_open())
+        return;
+
+    // The default value in RouteTree::update_from_heap() is -1; only calls which descend from route_net()
+    // pass in an iteration value, which is the only context in which we want to profile.
     if (iteration < 1)
         return;
 
-    for (size_t i = 2; i < branch_inodes.size(); ++i) { /* Distance one node away is always 0.0 (IPIN->SINK) */
-        RRNodeId source_inode = branch_inodes.back();
-        RRNodeId sink_inode = branch_inodes.front();
-        RRNodeId curr_inode = branch_inodes[i];
+    RRNodeId source_inode = branch_inodes.back();
+    RRNodeId sink_inode = branch_inodes.front();
 
-        float total_backward_cost = route_ctx.rr_node_route_inf[sink_inode].backward_path_cost;
-        float total_backward_delay = route_ctx.rr_node_route_inf[sink_inode].backward_path_delay;
-        float total_backward_congestion = route_ctx.rr_node_route_inf[sink_inode].backward_path_congestion;
+    VTR_ASSERT(rr_graph.node_type(source_inode) == SOURCE);
+    VTR_ASSERT(rr_graph.node_type(sink_inode) == SINK);
 
-        auto current_node = route_ctx.rr_node_route_inf[curr_inode];
-        float current_backward_cost = current_node.backward_path_cost;
-        float current_backward_delay = current_node.backward_path_delay;
-        float current_backward_congestion = current_node.backward_path_congestion;
+    /* Get sink node attributes (atom block name, atom block model, cluster type, tile dimensions) */
 
-        auto [from_x, from_y] = util::get_adjusted_rr_position(curr_inode);
-        auto [to_x, to_y] = util::get_adjusted_rr_position(sink_inode);
+    if (atom_block_names.find(sink_inode) == atom_block_names.end()) {
+        if (net_id != ParentNetId::INVALID() && target_net_pin_index != OPEN) {
+            atom_block_names[sink_inode] = net_list.block_name(net_list.net_pin_block(net_id, target_net_pin_index));
 
-        int delta_x = to_x - from_x;
-        int delta_y = to_y - from_y;
+            AtomBlockId atom_block_id = g_vpr_ctx.atom().nlist.find_block(atom_block_names[sink_inode]);
+            atom_block_models[sink_inode] = g_vpr_ctx.atom().nlist.block_model(atom_block_id)->name;
 
-        float djikstra_cost = total_backward_cost - current_backward_cost;
-        float djikstra_delay = total_backward_delay - current_backward_delay;
-        float djikstra_congestion = total_backward_congestion - current_backward_congestion;
+            ClusterBlockId cluster_block_id = atom_to_cluster(atom_block_id);
 
-        float lookahead_cost = router_lookahead.get_expected_cost(curr_inode, sink_inode, cost_params, 0.0);
-        auto [lookahead_delay, lookahead_congestion] = router_lookahead.get_expected_delay_and_cong(curr_inode, sink_inode, cost_params, 0.0);
+            cluster_block_types[sink_inode] = g_vpr_ctx.clustering().clb_nlist.block_type(cluster_block_id)->name;
+
+            auto tile_type = physical_tile_type(cluster_block_id);
+            tile_dimensions[sink_inode] = std::pair(std::to_string(tile_type->width), std::to_string(tile_type->height));
+        } else {
+            atom_block_names[sink_inode] = "--";
+            atom_block_models[sink_inode] = "--";
+            cluster_block_types[sink_inode] = "--";
+            tile_dimensions[sink_inode] = {"--", "--"};
+        }
+    }
 
-        if (atom_block_names.find(sink_inode) == atom_block_names.end()) {
-            if (net_id != ParentNetId::INVALID() && target_net_pin_index != OPEN) {
-                atom_block_names[sink_inode] = net_list.block_name(net_list.net_pin_block(net_id, target_net_pin_index));
+    VTR_ASSERT_SAFE(atom_block_models.find(sink_inode) != atom_block_models.end());
+    VTR_ASSERT_SAFE(cluster_block_types.find(sink_inode) != cluster_block_types.end());
+    VTR_ASSERT_SAFE(tile_dimensions.find(sink_inode) != tile_dimensions.end());
 
-                AtomBlockId atom_block_id = g_vpr_ctx.atom().nlist.find_block(atom_block_names[sink_inode]);
-                atom_block_models[sink_inode] = g_vpr_ctx.atom().nlist.block_model(atom_block_id)->name;
+    std::string block_name = atom_block_names[sink_inode];
+    std::string atom_block_model = atom_block_models[sink_inode];
+    std::string cluster_block_type = cluster_block_types[sink_inode];
+    auto [tile_width, tile_height] = tile_dimensions[sink_inode];
 
-                ClusterBlockId cluster_block_id = atom_to_cluster(atom_block_id);
+    /* Iterate through the given path and record information for each node */
+    for (size_t i = 2; i < branch_inodes.size(); ++i) { // Distance one node away is always 0. (IPIN->SINK)
+        RRNodeId curr_inode = branch_inodes[i];
 
-                cluster_block_types[sink_inode] = g_vpr_ctx.clustering().clb_nlist.block_type(cluster_block_id)->name;
+        // Get backwards path cost, delay, and congestion from sink node
+        t_rr_node_route_inf sink_node_info = route_ctx.rr_node_route_inf[sink_inode];
+        float total_backward_cost = sink_node_info.backward_path_cost;
+        float total_backward_delay = sink_node_info.backward_path_delay;
+        float total_backward_congestion = sink_node_info.backward_path_congestion;
+
+        // Get backwards path cost, delay, and congestion from current node
+        t_rr_node_route_inf curr_node_info = route_ctx.rr_node_route_inf[curr_inode];
+        float current_backward_cost = curr_node_info.backward_path_cost;
+        float current_backward_delay = curr_node_info.backward_path_delay;
+        float current_backward_congestion = curr_node_info.backward_path_congestion;
+
+        // Get the difference in the coordinates in the current and sink nodes.
+        // Note: we are not using util::get_xy_deltas() because this always gives positive values
+        // unless the current node is the source node. Using util::get_adjusted_rr_position therefore
+        // gives us more information.
+        auto [from_x, from_y] = util::get_adjusted_rr_position(curr_inode);
+        auto [to_x, to_y] = util::get_adjusted_rr_position(sink_inode);
 
-                auto tile_type = physical_tile_type(cluster_block_id);
-                tile_dimensions[sink_inode] = std::pair(std::to_string(tile_type->width), std::to_string(tile_type->height));
-            } else {
-                atom_block_names[sink_inode] = "--";
-                atom_block_models[sink_inode] = "--";
-                cluster_block_types[sink_inode] = "--";
-                tile_dimensions[sink_inode] = {"--", "--"};
-            }
-        }
+        int delta_x = to_x - from_x;
+        int delta_y = to_y - from_y;
 
-        VTR_ASSERT_SAFE(atom_block_names.find(sink_inode) != atom_block_names.end());
-        VTR_ASSERT_SAFE(atom_block_models.find(sink_inode) != atom_block_models.end());
-        VTR_ASSERT_SAFE(cluster_block_types.find(sink_inode) != cluster_block_types.end());
-        VTR_ASSERT_SAFE(tile_dimensions.find(sink_inode) != tile_dimensions.end());
+        // Calculate the actual cost, delay, and congestion from the current node to the sink.
+        float actual_cost = total_backward_cost - current_backward_cost;
+        float actual_delay = total_backward_delay - current_backward_delay;
+        float actual_congestion = total_backward_congestion - current_backward_congestion;
 
-        std::string block_name = atom_block_names[sink_inode];
-        std::string atom_block_model = atom_block_models[sink_inode];
-        std::string cluster_block_type = cluster_block_types[sink_inode];
-        auto [tile_width, tile_height] = tile_dimensions[sink_inode];
+        // Get the cost, delay, and congestion estimates made by the lookahead.
+        // Note: lookahead_cost = lookahead_delay * criticality + lookahead_congestion * (1. - criticality)
+        float lookahead_cost = router_lookahead.get_expected_cost(curr_inode, sink_inode, cost_params, 0.0);
+        auto [lookahead_delay, lookahead_congestion] = router_lookahead.get_expected_delay_and_cong(curr_inode, sink_inode, cost_params, 0.0);
 
+        // Get the current node's type and length
         std::string node_type_str = rr_graph.node_type_string(curr_inode);
         std::string node_length = (node_type_str == "CHANX" || node_type_str == "CHANX")
                                       ? std::to_string(rr_graph.node_length(curr_inode))
                                       : "--";
 
+        /* Write out all info */
+
         lookahead_verifier_csv << iteration << ",";            // iteration no.
         lookahead_verifier_csv << source_inode << ",";         // source node
         lookahead_verifier_csv << sink_inode << ",";           // sink node
@@ -143,9 +162,9 @@ void LookaheadProfiler::record(int iteration,
         lookahead_verifier_csv << i << ",";                    // num. nodes from sink
         lookahead_verifier_csv << delta_x << ",";              // delta x
         lookahead_verifier_csv << delta_y << ",";              // delta y
-        lookahead_verifier_csv << djikstra_cost << ",";        // actual cost
-        lookahead_verifier_csv << djikstra_delay << ",";       // actual delay
-        lookahead_verifier_csv << djikstra_congestion << ",";  // actual congestion
+        lookahead_verifier_csv << actual_cost << ",";          // actual cost
+        lookahead_verifier_csv << actual_delay << ",";         // actual delay
+        lookahead_verifier_csv << actual_congestion << ",";    // actual congestion
         lookahead_verifier_csv << lookahead_cost << ",";       // predicted cost
         lookahead_verifier_csv << lookahead_delay << ",";      // predicted delay
         lookahead_verifier_csv << lookahead_congestion << ","; // predicted congestion

vpr/src/route/lookahead_profiler.h

@@ -3,14 +3,35 @@
 
 #include <fstream>
 #include <thread>
-#include "rr_graph_fwd.h"
+
 #include "connection_router_interface.h"
 #include "router_lookahead.h"
+#include "rr_graph_fwd.h"
 
+/**
+ * @brief A class which records information used to profile the router lookahead: most importantly,
+ * the actual cost (delay and congestion) from nodes to the sink to which they have been routed, as
+ * well as the lookahead's estimation of this cost.
+ */
 class LookaheadProfiler {
   public:
-    LookaheadProfiler();
+    LookaheadProfiler()
+        : is_empty(true) {}
 
+    /**
+     * @brief Record information on nodes on a path from a source to a sink.
+     *
+     * @param iteration The router iteration.
+     * @param target_net_pin_index Target pin of this sink in the net.
+     * @param cost_params
+     * @param router_lookahead
+     * @param net_id
+     * @param net_list
+     * @param branch_inodes A path from a sink to its source, as a vector of nodes.
+     *
+     * @warning
+     * branch_inodes must be a backwards path, from a sink node to a source node.
+     */
     void record(int iteration,
                 int target_net_pin_index,
                 const t_conn_cost_params& cost_params,
@@ -20,11 +41,17 @@ class LookaheadProfiler {
                 std::vector<RRNodeId> branch_inodes);
 
   private:
+    ///@breif The output filestream.
     std::ofstream lookahead_verifier_csv;
+    ///@brief Whether the output file is empty/not yet opened.
     bool is_empty;
+    ///@brief A map from sink node IDs to the names of their atom blocks.
     std::unordered_map<RRNodeId, std::string> atom_block_names;
+    ///@brief A map from sink node IDs to the names of the models of their atom blocks.
     std::unordered_map<RRNodeId, std::string> atom_block_models;
+    ///@brief A map from sink node IDs to the names of the types of their clusters.
     std::unordered_map<RRNodeId, std::string> cluster_block_types;
+    ///@brief A map from sink node IDs to the dimensions of their tiles (width, height).
     std::unordered_map<RRNodeId, std::pair<std::string, std::string>> tile_dimensions;
 };