Re-compute NoC costs when a placement checkpoint is restored.

If the current router placement is different from the one in the checkpoint, NoC-related costs and internal data structures need to be re-computed and re-initialized to match the placement in the checkpoint. This is done by calling reinitialize_noc_routing() in restore_best_placement().

Author: soheilshahrouz

vpr/src/noc/noc_storage.cpp

@@ -23,6 +23,10 @@ const vtr::vector<NocLinkId, NocLink>& NocStorage::get_noc_links(void) const {
     return link_storage;
 }
 
+vtr::vector<NocLinkId, NocLink>& NocStorage::get_mutable_noc_links(void) {
+    return link_storage;
+}
+
 int NocStorage::get_number_of_noc_links(void) const {
     return link_storage.size();
 }

vpr/src/noc/noc_storage.h

@@ -184,6 +184,15 @@ class NocStorage {
      */
     const vtr::vector<NocLinkId, NocLink>& get_noc_links(void) const;
 
+    /**
+     * @brief Get all the links in the NoC. The links themselves can
+     * be modified. This function should be used when information on
+     * every link needs to be modified.
+     *
+     * @return A vector of links.
+     */
+    vtr::vector<NocLinkId, NocLink>& get_mutable_noc_links(void);
+
     /**
      * @return An integer representing the total number of links within the
      * NoC.

vpr/src/place/initial_placement.cpp

@@ -1105,7 +1105,7 @@ void initial_placement(enum e_pad_loc_type pad_loc_type, const char* constraints
 
     // route all the traffic flows in the NoC now that all the router cluster block have been placed  (this is done only if the noc optimization is enabled by the user)
     if (noc_enabled) {
-        initial_noc_placement();
+        initial_noc_routing();
     }
 
     //#ifdef VERBOSE

vpr/src/place/noc_place_utils.cpp

@@ -9,7 +9,7 @@ static vtr::vector<NocTrafficFlowId, TrafficFlowPlaceCost> traffic_flow_costs, p
 static std::vector<NocTrafficFlowId> affected_traffic_flows;
 /*********************************************************** *****************************/
 
-void initial_noc_placement(void) {
+void initial_noc_routing(void) {
     // need to get placement information about where the router cluster blocks are placed on the device
     const auto& place_ctx = g_vpr_ctx.placement();
 
@@ -37,6 +37,22 @@ void initial_noc_placement(void) {
     return;
 }
 
+void reinitialize_noc_routing(const t_noc_opts& noc_opts, t_placer_costs& costs) {
+    auto& noc_ctx = g_vpr_ctx.mutable_noc();
+
+    // Zero out bandwidth usage for all links
+    for (auto& noc_link : noc_ctx.noc_model.get_mutable_noc_links()) {
+        noc_link.set_bandwidth_usage(0.0);
+    }
+
+    // Route traffic flows and update link bandwidth usage
+    initial_noc_routing();
+
+    // Initialize traffic_flow_costs
+    costs.noc_aggregate_bandwidth_cost = comp_noc_aggregate_bandwidth_cost();
+    costs.noc_latency_cost = comp_noc_latency_cost(noc_opts);
+}
+
 void find_affected_noc_routers_and_update_noc_costs(const t_pl_blocks_to_be_moved& blocks_affected, double& noc_aggregate_bandwidth_delta_c, double& noc_latency_delta_c, const t_noc_opts& noc_opts) {
     // provides the positions where the affected blocks have moved to
     auto& place_ctx = g_vpr_ctx.placement();

vpr/src/place/noc_place_utils.h

@@ -49,7 +49,23 @@ struct TrafficFlowPlaceCost {
  * routed. This is why this function should only be used once.
  * 
  */
-void initial_noc_placement(void);
+void initial_noc_routing(void);
+
+/**
+ * @brief Zeros out all link bandwidth usage an re-routes traffic flows.
+ * Initializes static variables in noc_place_utils.cpp that are used to
+ * keep track of NoC-related costs.
+ *
+ * This function should be called when a placement checkpoint is restored.
+ * If the router placement in the checkpoint is different from the last
+ * router placement before the checkpoint is restored, link bandwidth usage,
+ * traffic flow routes, and static variable in noc_place_utils.cpp are no
+ * longer valid and need to be re-initialized.
+ *
+ * @param noc_opts NoC-related options used to calculated NoC costs
+ * @param costs Used to get aggregate bandwidth and latency costs.
+ */
+void reinitialize_noc_routing(const t_noc_opts& noc_opts, t_placer_costs& costs);
 
 /**
  * @brief Goes through all the cluster blocks that were moved

vpr/src/place/place.cpp

@@ -953,7 +953,7 @@ void try_place(const Netlist<>& net_list,
     if (placer_opts.place_checkpointing)
         restore_best_placement(placement_checkpoint, timing_info, costs,
                                placer_criticalities, placer_setup_slacks, place_delay_model,
-                               pin_timing_invalidator, crit_params);
+                               pin_timing_invalidator, crit_params, noc_opts);
 
     if (placer_opts.placement_saves_per_temperature >= 1) {
         std::string filename = vtr::string_fmt("placement_%03d_%03d.place",

vpr/src/place/place_checkpoint.cpp

@@ -1,4 +1,5 @@
 #include "place_checkpoint.h"
+#include "noc_place_utils.h"
 
 float t_placement_checkpoint::get_cp_cpd() { return cpd; }
 double t_placement_checkpoint::get_cp_bb_cost() { return costs.bb_cost; }
@@ -26,7 +27,7 @@ void save_placement_checkpoint_if_needed(t_placement_checkpoint& placement_check
     }
 }
 
-void restore_best_placement(t_placement_checkpoint& placement_checkpoint, std::shared_ptr<SetupTimingInfo>& timing_info, t_placer_costs& costs, std::unique_ptr<PlacerCriticalities>& placer_criticalities, std::unique_ptr<PlacerSetupSlacks>& placer_setup_slacks, std::unique_ptr<PlaceDelayModel>& place_delay_model, std::unique_ptr<NetPinTimingInvalidator>& pin_timing_invalidator, PlaceCritParams crit_params) {
+void restore_best_placement(t_placement_checkpoint& placement_checkpoint, std::shared_ptr<SetupTimingInfo>& timing_info, t_placer_costs& costs, std::unique_ptr<PlacerCriticalities>& placer_criticalities, std::unique_ptr<PlacerSetupSlacks>& placer_setup_slacks, std::unique_ptr<PlaceDelayModel>& place_delay_model, std::unique_ptr<NetPinTimingInvalidator>& pin_timing_invalidator, PlaceCritParams crit_params, const t_noc_opts& noc_opts) {
     if (placement_checkpoint.cp_is_valid() && timing_info->least_slack_critical_path().delay() > placement_checkpoint.get_cp_cpd() && costs.bb_cost < 1.05 * placement_checkpoint.get_cp_bb_cost()) {
         //restore the latest placement checkpoint
         costs = placement_checkpoint.restore_placement();
@@ -43,6 +44,11 @@ void restore_best_placement(t_placement_checkpoint& placement_checkpoint, std::s
                                    timing_info.get(),
                                    &costs);
 
+        // If NoC is enabled, re-compute NoC costs and re-initialize NoC internal data structures
+        if (noc_opts.noc) {
+            reinitialize_noc_routing(noc_opts, costs);
+        }
+
         VTR_LOG("\nCheckpoint restored\n");
     }
 }

vpr/src/place/place_checkpoint.h

@@ -50,5 +50,5 @@ class t_placement_checkpoint {
 void save_placement_checkpoint_if_needed(t_placement_checkpoint& placement_checkpoint, std::shared_ptr<SetupTimingInfo> timing_info, t_placer_costs& costs, float cpd);
 
 //restore the checkpoint if it's better than the latest placement solution
-void restore_best_placement(t_placement_checkpoint& placement_checkpoint, std::shared_ptr<SetupTimingInfo>& timing_info, t_placer_costs& costs, std::unique_ptr<PlacerCriticalities>& placer_criticalities, std::unique_ptr<PlacerSetupSlacks>& placer_setup_slacks, std::unique_ptr<PlaceDelayModel>& place_delay_model, std::unique_ptr<NetPinTimingInvalidator>& pin_timing_invalidator, PlaceCritParams crit_params);
+void restore_best_placement(t_placement_checkpoint& placement_checkpoint, std::shared_ptr<SetupTimingInfo>& timing_info, t_placer_costs& costs, std::unique_ptr<PlacerCriticalities>& placer_criticalities, std::unique_ptr<PlacerSetupSlacks>& placer_setup_slacks, std::unique_ptr<PlaceDelayModel>& place_delay_model, std::unique_ptr<NetPinTimingInvalidator>& pin_timing_invalidator, PlaceCritParams crit_params, const t_noc_opts& noc_opts);
 #endif