rsz: repairSetup: Restrict number of repairs per iteration to avoid f…

…alling into local optimums

Signed-off-by: Eryk Szpotanski <[email protected]>

src/rsz/README.md

@@ -289,6 +289,7 @@ repair_timing
     [-skip_last_gasp]
     [-repair_tns tns_end_percent]
     [-max_passes passes]
+    [-max_passes_per_iter passes]
     [-max_utilization util]
     [-max_buffer_percent buffer_percent]
     [-match_cell_footprint]
@@ -311,6 +312,7 @@ repair_timing
 | `-skip_buffer_removal` | Flag to skip buffer removal.  The default is to perform buffer removal transform during setup fixing. |
 | `-skip_last_gasp` | Flag to skip final ("last gasp") optimizations.  The default is to perform greedy sizing at the end of optimization. |
 | `-repair_tns` | Percentage of violating endpoints to repair (0-100). When `tns_end_percent` is zero, only the worst endpoint is repaired. When `tns_end_percent` is 100 (default), all violating endpoints are repaired. |
+| `-max_passes_per_iter` | Max number of repairs per iteration for `rsz::repairSetup`. |
 | `-max_utilization` | Defines the percentage of core area used. |
 | `-max_buffer_percent` | Specify a maximum number of buffers to insert to repair hold violations as a percentage of the number of instances in the design. The default value is `20`, and the allowed values are integers `[0, 100]`. |
 | `-match_cell_footprint` | Obey the Liberty cell footprint when swapping gates. |

src/rsz/src/RepairSetup.cc

@@ -60,6 +60,7 @@ namespace rsz {
 
 using std::max;
 using std::pair;
+using std::set;
 using std::string;
 using std::vector;
 using utl::RSZ;
@@ -87,9 +88,21 @@ void RepairSetup::init()
   db_network_ = resizer_->db_network_;
 }
 
+struct SlackVertexPairComp
+{
+  bool operator()(const pair<Vertex*, Slack>& end_slack1,
+                  const pair<Vertex*, Slack>& end_slack2) const
+  {
+    return end_slack1.second < end_slack2.second
+           || (end_slack1.second == end_slack2.second
+               && end_slack1.first->objectIdx()
+                      < end_slack2.first->objectIdx());
+  }
+};
+
 bool RepairSetup::repairSetup(const float setup_slack_margin,
                               const double repair_tns_end_percent,
-                              const int max_passes,
+                              const int max_passes_per_iter,
                               const bool verbose,
                               const bool skip_pin_swap,
                               const bool skip_gate_cloning,
@@ -110,7 +123,7 @@ bool RepairSetup::repairSetup(const float setup_slack_margin,
 
   // Sort failing endpoints by slack.
   const VertexSet* endpoints = sta_->endpoints();
-  vector<pair<Vertex*, Slack>> violating_ends;
+  set<pair<Vertex*, Slack>, SlackVertexPairComp> violating_ends;
   // logger_->setDebugLevel(RSZ, "repair_setup", 2);
   // Should check here whether we can figure out the clock domain for each
   // vertex. This may be the place where we can do some round robin fun to
@@ -119,14 +132,9 @@ bool RepairSetup::repairSetup(const float setup_slack_margin,
   for (Vertex* end : *endpoints) {
     const Slack end_slack = sta_->vertexSlack(end, max_);
     if (end_slack < setup_slack_margin) {
-      violating_ends.emplace_back(end, end_slack);
+      violating_ends.emplace(end, end_slack);
     }
   }
-  std::stable_sort(violating_ends.begin(),
-                   violating_ends.end(),
-                   [](const auto& end_slack1, const auto& end_slack2) {
-                     return end_slack1.second < end_slack2.second;
-                   });
   debugPrint(logger_,
              RSZ,
              "repair_setup",
@@ -174,8 +182,9 @@ bool RepairSetup::repairSetup(const float setup_slack_margin,
     printProgress(opto_iteration, false, false, false, num_viols);
   }
   float fix_rate_threshold = inc_fix_rate_threshold_;
-  for (const auto& end_original_slack : violating_ends) {
-    Vertex* end = end_original_slack.first;
+  while (num_viols > 0 && !violating_ends.empty()) {
+    Vertex* end = violating_ends.begin()->first;
+    violating_ends.erase(violating_ends.begin());
     Slack end_slack = sta_->vertexSlack(end, max_);
     Slack worst_slack;
     Vertex* worst_vertex;
@@ -202,14 +211,14 @@ bool RepairSetup::repairSetup(const float setup_slack_margin,
                  " max_end_count {}", end->name(network_), end_index,
                  max_end_count);
       // clang-format on
-      break;
+      continue;
     }
     Slack prev_end_slack = end_slack;
     Slack prev_worst_slack = worst_slack;
     int pass = 1;
     int decreasing_slack_passes = 0;
     resizer_->journalBegin();
-    while (pass <= max_passes) {
+    while (pass <= max_passes_per_iter) {
       opto_iteration++;
       if (verbose) {
         printProgress(opto_iteration, false, false, false, num_viols);
@@ -328,7 +337,8 @@ bool RepairSetup::repairSetup(const float setup_slack_margin,
         // Allow slack to increase to get out of local minima.
         // Do not update prev_end_slack so it saves the high water mark.
         decreasing_slack_passes++;
-        if (decreasing_slack_passes > decreasing_slack_max_passes_) {
+        if (decreasing_slack_passes > decreasing_slack_max_passes_
+            || pass == max_passes_per_iter) {
           // Undo changes that reduced slack.
           debugPrint(logger_,
                      RSZ,
@@ -350,9 +360,10 @@ bool RepairSetup::repairSetup(const float setup_slack_margin,
                                    removed_buffer_count_);
           // clang-format off
           debugPrint(logger_, RSZ, "repair_setup", 1, "bailing out {} decreasing"
-                     " passes {} > decreasig pass limit {}", end->name(network_),
-                     decreasing_slack_passes, decreasing_slack_max_passes_);
+                     " passes {} > decreasig pass limit {} or pass {} > max passes per iteration {}", end->name(network_),
+                     decreasing_slack_passes, decreasing_slack_max_passes_, pass, max_passes_per_iter);
           // clang-format on
+          ++pass;
           break;
         }
       }
@@ -370,6 +381,10 @@ bool RepairSetup::repairSetup(const float setup_slack_margin,
       }
       pass++;
     }  // while pass <= max_passes
+    if (pass == max_passes_per_iter + 1) {
+      // If violation was not fixed, placed it back to the queue
+      violating_ends.emplace(end, worst_slack);
+    }
     if (verbose) {
       printProgress(opto_iteration, true, false, false, num_viols);
     }

src/rsz/src/RepairSetup.hh

@@ -128,7 +128,7 @@ class RepairSetup : public sta::dbStaState
                    // Percent of violating ends to repair to
                    // reduce tns (0.0-1.0).
                    double repair_tns_end_percent,
-                   int max_passes,
+                   int max_passes_per_iter,
                    bool verbose,
                    bool skip_pin_swap,
                    bool skip_gate_cloning,

src/rsz/src/Resizer.i

@@ -595,7 +595,7 @@ repair_net_cmd(Net *net,
 bool
 repair_setup(double setup_margin,
              double repair_tns_end_percent,
-             int max_passes,
+             int max_passes_per_iter,
              bool match_cell_footprint, bool verbose,
              bool skip_pin_swap, bool skip_gate_cloning,
              bool skip_buffering, bool skip_buffer_removal,
@@ -604,7 +604,7 @@ repair_setup(double setup_margin,
   ensureLinked();
   Resizer *resizer = getResizer();
   return resizer->repairSetup(setup_margin, repair_tns_end_percent,
-                       max_passes, match_cell_footprint, verbose,
+                       max_passes_per_iter, match_cell_footprint, verbose,
                        skip_pin_swap, skip_gate_cloning,
                        skip_buffering, skip_buffer_removal,
                        skip_last_gasp);

src/rsz/src/Resizer.tcl

@@ -537,6 +537,7 @@ sta::define_cmd_args "repair_timing" {[-setup] [-hold]\
                                         [-skip_last_gasp]\
                                         [-repair_tns tns_end_percent]\
                                         [-max_passes passes]\
+                                        [-max_passes_per_iter passes_per_iter]\
                                         [-max_buffer_percent buffer_percent]\
                                         [-max_utilization util] \
                                         [-match_cell_footprint] \
@@ -546,7 +547,7 @@ proc repair_timing { args } {
   sta::parse_key_args "repair_timing" args \
     keys {-setup_margin -hold_margin -slack_margin \
             -libraries -max_utilization -max_buffer_percent \
-            -recover_power -repair_tns -max_passes} \
+            -recover_power -repair_tns -max_passes -max_passes_per_iter} \
     flags {-setup -hold -allow_setup_violations -skip_pin_swap -skip_gate_cloning \
            -skip_buffering -skip_buffer_removal -skip_last_gasp -match_cell_footprint \
            -verbose}
@@ -612,6 +613,11 @@ proc repair_timing { args } {
     set max_passes $keys(-max_passes)
   }
 
+  set max_passes_per_iter 20
+  if { [info exists keys(-max_passes_per_iter)] } {
+    set max_passes_per_iter $keys(-max_passes_per_iter)
+  }
+
   set match_cell_footprint [info exists flags(-match_cell_footprint)]
   if { [design_is_routed] } {
     rsz::set_parasitics_src "detailed_routing"
@@ -627,8 +633,8 @@ proc repair_timing { args } {
     set recovered_power [rsz::recover_power $recover_power_percent $match_cell_footprint]
   } else {
     if { $setup } {
-      set repaired_setup [rsz::repair_setup $setup_margin $repair_tns_end_percent $max_passes \
-        $match_cell_footprint $verbose \
+      set repaired_setup [rsz::repair_setup $setup_margin $repair_tns_end_percent \
+        $max_passes_per_iter $match_cell_footprint $verbose \
         $skip_pin_swap $skip_gate_cloning $skip_buffering \
         $skip_buffer_removal $skip_last_gasp]
     }