Add critical path scheduler to improve build times

src/build.cc

@@ -75,6 +75,7 @@ bool DryRunCommandRunner::WaitForCommand(Result* result) {
 
 }  // namespace
 
+
 Plan::Plan(Builder* builder)
   : builder_(builder)
   , command_edges_(0)
@@ -89,6 +90,7 @@ void Plan::Reset() {
 }
 
 bool Plan::AddTarget(const Node* target, string* err) {
+  targets_.push_back(target);
   return AddSubTarget(target, NULL, err, NULL);
 }
 
@@ -151,10 +153,10 @@ void Plan::EdgeWanted(const Edge* edge) {
 Edge* Plan::FindWork() {
   if (ready_.empty())
     return NULL;
-  EdgeSet::iterator e = ready_.begin();
-  Edge* edge = *e;
-  ready_.erase(e);
-  return edge;
+
+  Edge* work = ready_.top();
+  ready_.pop();
+  return work;
 }
 
 void Plan::ScheduleWork(map<Edge*, Want>::iterator want_e) {
@@ -172,10 +174,12 @@ void Plan::ScheduleWork(map<Edge*, Want>::iterator want_e) {
   Pool* pool = edge->pool();
   if (pool->ShouldDelayEdge()) {
     pool->DelayEdge(edge);
-    pool->RetrieveReadyEdges(&ready_);
+    EdgeSet new_edges;
+    pool->RetrieveReadyEdges(&new_edges);
+    ready_.push_multiple(new_edges.begin(), new_edges.end());
   } else {
     pool->EdgeScheduled(*edge);
-    ready_.insert(edge);
+    ready_.push(edge);
   }
 }
 
@@ -187,7 +191,9 @@ bool Plan::EdgeFinished(Edge* edge, EdgeResult result, string* err) {
   // See if this job frees up any delayed jobs.
   if (directly_wanted)
     edge->pool()->EdgeFinished(*edge);
-  edge->pool()->RetrieveReadyEdges(&ready_);
+  EdgeSet new_edges;
+  edge->pool()->RetrieveReadyEdges(&new_edges);
+  ready_.push_multiple(new_edges.begin(), new_edges.end());
 
   // The rest of this function only applies to successful commands.
   if (result != kEdgeSucceeded)
@@ -424,6 +430,150 @@ void Plan::UnmarkDependents(const Node* node, set<Node*>* dependents) {
   }
 }
 
+namespace {
+
+template <typename T>
+struct SeenBefore {
+  std::set<const T*>* seen_;
+
+  SeenBefore(std::set<const T*>* seen) : seen_(seen) {}
+
+  bool operator() (const T* item) {
+    // Return true if the item has been seen before
+    return !seen_->insert(item).second;
+  }
+};
+
+// Assign run_time_ms_ for all wanted edges, and returns total time for all edges
+// For phony edges, 0 cost.
+// For edges with a build history, use the last build time.
+// For edges without history, use the 75th percentile time for edges with history.
+// Or, if there is no history at all just use 1
+int64_t AssignEdgeRuntime(BuildLog* build_log,
+                          const std::map<Edge*, Plan::Want>& want) {
+  bool missing_durations = false;
+  std::vector<int64_t> durations;
+  int64_t total_time = 0;
+
+  for (std::map<Edge*, Plan::Want>::const_iterator it = want.begin(),
+                                                   end = want.end();
+       it != end; ++it) {
+    Edge* edge = it->first;
+    if (edge->is_phony()) {
+      continue;
+    }
+    BuildLog::LogEntry* entry =
+        build_log->LookupByOutput(edge->outputs_[0]->path());
+    if (!entry) {
+      missing_durations = true;
+      edge->run_time_ms_ = -1;  // -1 to mark as needing filled in
+      continue;
+    }
+    const int64_t duration = entry->end_time - entry->start_time;
+    edge->run_time_ms_ = duration;
+    total_time += duration;
+    durations.push_back(duration);
+  }
+
+  if (!missing_durations) {
+    return total_time;
+  }
+
+  // Heuristic: for unknown edges, take the 75th percentile time.
+  // This allows the known-slowest jobs to run first, but isn't so
+  // small that it is always the lowest priority. Which for slow jobs,
+  // might bottleneck the build.
+  int64_t p75_time = 1;
+  int64_t num_durations = static_cast<int64_t>(durations.size());
+  if (num_durations > 0) {
+    size_t p75_idx = (num_durations - 1) - num_durations / 4;
+    std::vector<int64_t>::iterator p75_it = durations.begin() + p75_idx;
+    std::nth_element(durations.begin(), p75_it, durations.end());
+    p75_time = *p75_it;
+  }
+
+  for (std::map<Edge*, Plan::Want>::const_iterator it = want.begin(),
+                                                   end = want.end();
+       it != end; ++it) {
+    Edge* edge = it->first;
+    if (edge->run_time_ms_ >= 0) {
+      continue;
+    }
+    edge->run_time_ms_ = p75_time;
+    total_time += p75_time;
+  }
+  return total_time;
+}
+
+}  // namespace
+
+void Plan::ComputeCriticalTime(BuildLog* build_log) {
+  // testcases have no build_log
+  if (!build_log)
+    return;
+
+  METRIC_RECORD("ComputePriorityList");
+  // Remove duplicate targets
+  {
+    std::set<const Node*> seen;
+    SeenBefore<Node> seen_before(&seen);
+    targets_.erase(std::remove_if(targets_.begin(), targets_.end(), seen_before),
+                   targets_.end());
+  }
+
+  // total time if building all edges in serial. This value is big
+  // enough to ensure higher priority target's initial critical time
+  // is always bigger than lower ones
+  int64_t total_time = AssignEdgeRuntime(build_log, want_);
+
+  // Use backflow algorithm to compute critical times for all nodes, starting
+  // from the destination nodes.
+  // XXX: ignores pools
+  std::queue<Edge*> breadthFirstEdges;  // Queue, for breadth-first traversal
+  std::set<const Edge*> active_edges;   // Set of in breadthFirstEdges
+  SeenBefore<Edge> seen_edge(
+      &active_edges);  // Test for uniqueness in breadthFirstEdges
+
+  for (std::vector<const Node*>::reverse_iterator it = targets_.rbegin(),
+                                                  end = targets_.rend();
+       it != end; ++it) {
+    if (Edge* in = (*it)->in_edge()) {
+      // Use initial critical time: total_time * N. This means higher
+      // priority targets always get a higher critical time value
+      int64_t priority_weight = (it - targets_.rbegin()) * total_time;
+      in->set_critical_time(
+          priority_weight +
+          std::max<int64_t>(in->run_time_ms_, in->critical_time()));
+      if (!seen_edge(in)) {
+        breadthFirstEdges.push(in);
+      }
+    }
+  }
+
+  while (!breadthFirstEdges.empty()) {
+    Edge* e = breadthFirstEdges.front();
+    breadthFirstEdges.pop();
+    active_edges.erase(e);
+
+    for (std::vector<Node*>::iterator it = e->inputs_.begin(),
+                                      end = e->inputs_.end();
+         it != end; ++it) {
+      Edge* in = (*it)->in_edge();
+      if (!in) {
+        continue;
+      }
+      // Only process edge if this node offers a higher critical time
+      const int64_t proposed_time = e->critical_time() + in->run_time_ms_;
+      if (proposed_time > in->critical_time()) {
+        in->set_critical_time(proposed_time);
+        if (!seen_edge(in)) {
+          breadthFirstEdges.push(in);
+        }
+      }
+    }
+  }
+}
+
 void Plan::Dump() const {
   printf("pending: %d\n", (int)want_.size());
   for (map<Edge*, Want>::const_iterator e = want_.begin(); e != want_.end(); ++e) {
@@ -574,6 +724,8 @@ bool Builder::AlreadyUpToDate() const {
 bool Builder::Build(string* err) {
   assert(!AlreadyUpToDate());
 
+  plan_.ComputeCriticalTime(scan_.build_log());
+
   status_->PlanHasTotalEdges(plan_.command_edge_count());
   int pending_commands = 0;
   int failures_allowed = config_.failures_allowed;

src/build.h

@@ -18,7 +18,6 @@
 #include <cstdio>
 #include <map>
 #include <memory>
-#include <queue>
 #include <string>
 #include <vector>
 
@@ -35,6 +34,7 @@ struct Node;
 struct State;
 struct Status;
 
+
 /// Plan stores the state of a build plan: what we intend to build,
 /// which steps we're ready to execute.
 struct Plan {
@@ -75,22 +75,12 @@ struct Plan {
 
   /// Reset state.  Clears want and ready sets.
   void Reset();
+  void ComputeCriticalTime(BuildLog* build_log);
 
   /// Update the build plan to account for modifications made to the graph
   /// by information loaded from a dyndep file.
   bool DyndepsLoaded(DependencyScan* scan, const Node* node,
                      const DyndepFile& ddf, std::string* err);
-private:
-  bool RefreshDyndepDependents(DependencyScan* scan, const Node* node, std::string* err);
-  void UnmarkDependents(const Node* node, std::set<Node*>* dependents);
-  bool AddSubTarget(const Node* node, const Node* dependent, std::string* err,
-                    std::set<Edge*>* dyndep_walk);
-
-  /// Update plan with knowledge that the given node is up to date.
-  /// If the node is a dyndep binding on any of its dependents, this
-  /// loads dynamic dependencies from the node's path.
-  /// Returns 'false' if loading dyndep info fails and 'true' otherwise.
-  bool NodeFinished(Node* node, std::string* err);
 
   /// Enumerate possible steps we want for an edge.
   enum Want
@@ -105,6 +95,18 @@ struct Plan {
     kWantToFinish
   };
 
+private:
+  bool RefreshDyndepDependents(DependencyScan* scan, const Node* node, std::string* err);
+  void UnmarkDependents(const Node* node, std::set<Node*>* dependents);
+  bool AddSubTarget(const Node* node, const Node* dependent, std::string* err,
+                    std::set<Edge*>* dyndep_walk);
+
+  /// Update plan with knowledge that the given node is up to date.
+  /// If the node is a dyndep binding on any of its dependents, this
+  /// loads dynamic dependencies from the node's path.
+  /// Returns 'false' if loading dyndep info fails and 'true' otherwise.
+  bool NodeFinished(Node* node, std::string* err);
+
   void EdgeWanted(const Edge* edge);
   bool EdgeMaybeReady(std::map<Edge*, Want>::iterator want_e, std::string* err);
 
@@ -119,9 +121,11 @@ struct Plan {
   /// we want for the edge.
   std::map<Edge*, Want> want_;
 
-  EdgeSet ready_;
+  EdgeQueue ready_;
 
   Builder* builder_;
+  /// user provided targets in build order, earlier one have higher priority
+  std::vector<const Node*> targets_;
 
   /// Total number of edges that have commands (not phony).
   int command_edges_;

src/graph.h

@@ -18,6 +18,7 @@
 #include <set>
 #include <string>
 #include <vector>
+#include <queue>
 
 #include "dyndep.h"
 #include "eval_env.h"
@@ -146,9 +147,10 @@ struct Edge {
 
   Edge()
       : rule_(NULL), pool_(NULL), dyndep_(NULL), env_(NULL), mark_(VisitNone),
-        id_(0), outputs_ready_(false), deps_loaded_(false),
-        deps_missing_(false), generated_by_dep_loader_(false),
-        implicit_deps_(0), order_only_deps_(0), implicit_outs_(0) {}
+        id_(0), run_time_ms_(0), critical_time_(-1), outputs_ready_(false),
+        deps_loaded_(false), deps_missing_(false),
+        generated_by_dep_loader_(false), implicit_deps_(0), order_only_deps_(0),
+        implicit_outs_(0) {}
 
   /// Return true if all inputs' in-edges are ready.
   bool AllInputsReady() const;
@@ -171,6 +173,15 @@ struct Edge {
 
   void Dump(const char* prefix="") const;
 
+  // Critical time is the estimated exection time in ms of the edges
+  // forming the longest time-weighted path to the target output.
+  // This quantity is used as a priority during build scheduling.
+  // NOTE: Defaults to -1 as a marker smaller than any valid time
+  int64_t critical_time() const { return critical_time_; }
+  void set_critical_time(int64_t critical_time) {
+    critical_time_ = critical_time;
+  }
+
   const Rule* rule_;
   Pool* pool_;
   std::vector<Node*> inputs_;
@@ -179,6 +190,8 @@ struct Edge {
   BindingEnv* env_;
   VisitMark mark_;
   size_t id_;
+  int64_t run_time_ms_;
+  int64_t critical_time_;
   bool outputs_ready_;
   bool deps_loaded_;
   bool deps_missing_;
@@ -335,4 +348,32 @@ struct DependencyScan {
   DyndepLoader dyndep_loader_;
 };
 
+// Prioritize edges by largest critical time first
+struct EdgePriorityCompare {
+  bool operator()(const Edge* e1, const Edge* e2) const {
+    const int64_t ct1 = e1->critical_time();
+    const int64_t ct2 = e2->critical_time();
+    if (ct1 != ct2) {
+      return ct1 < ct2;
+    }
+    return e1->id_ < e2->id_;
+  }
+};
+
+// Set of ready edges, sorted by priority
+class EdgeQueue:
+  public std::priority_queue<Edge*, std::vector<Edge*>, EdgePriorityCompare>{
+public:
+  void clear() {
+    c.clear();
+  }
+
+  template <typename It>
+  void push_multiple(It first, It last) {
+    for (; first != last; ++first) {
+      push(*first);
+    }
+  }
+};
+
 #endif  // NINJA_GRAPH_H_