/* Copyright 2015 Google Inc. All Rights Reserved.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
==============================================================================*/

#include "tensorflow/core/graph/costmodel.h"

#include <vector>
#include "tensorflow/core/framework/step_stats.pb.h"
#include "tensorflow/core/graph/graph.h"
#include "tensorflow/core/platform/logging.h"

namespace tensorflow {
namespace {
const Microseconds kDefaultTimeEstimate(1);
const Microseconds kMinTimeEstimate(1);
}  // namespace

void CostModel::SuppressInfrequent() {
  // Find the median of the non-zero counts, and use half of its value
  // as the cutoff for a "normal" execution mode node.
  if (count_.empty()) return;
  std::vector<int32> non_zero;
  for (auto v : count_) {
    if (v > 0) non_zero.push_back(v);
  }
  const size_t sz = non_zero.size();
  if (sz > 0) {
    std::nth_element(non_zero.begin(), non_zero.begin() + sz / 2,
                     non_zero.end());
    int32 median_value = non_zero[sz / 2];
    min_count_ = median_value / 2;
    VLOG(1) << "num non_zero vals: " << non_zero.size() << " median_value "
            << median_value;
  } else {
    min_count_ = 1;
  }
}

void CostModel::MergeFromLocal(const Graph& g, const CostModel& cm) {
  CHECK(is_global_);
  CHECK(!cm.is_global());
  for (const Node* n : g.nodes()) {
    const int local_id = cm.Id(n);
    const int global_id = Id(n);
    if (local_id < 0 || global_id < 0) continue;
    Ensure(global_id);
    count_[global_id] += cm.count_[local_id];
    time_[global_id] += cm.time_[local_id];
    int num_slots = cm.slot_bytes_[local_id].size();
    if (num_slots > 0) {
      if (slot_bytes_[global_id].size() == 0) {
        slot_bytes_[global_id].resize(num_slots);
      } else {
        CHECK_EQ(num_slots, slot_bytes_[global_id].size());
      }
      for (int s = 0; s < num_slots; ++s) {
        slot_bytes_[global_id][s] += cm.slot_bytes_[local_id][s];
      }
    }
  }
}

void CostModel::MergeFromGlobal(const CostModel& cm) {
  CHECK(is_global_);
  CHECK_EQ(true, cm.is_global());
  const int num_nodes = cm.count_.size();
  Ensure(num_nodes);
  for (int i = 0; i < num_nodes; ++i) {
    count_[i] += cm.count_[i];
    time_[i] += cm.time_[i];
    int num_slots = cm.slot_bytes_[i].size();
    if (num_slots > 0) {
      if (slot_bytes_[i].size() == 0) {
        slot_bytes_[i].resize(num_slots);
      } else {
        CHECK_EQ(num_slots, slot_bytes_[i].size());
      }
      for (int s = 0; s < num_slots; ++s) {
        slot_bytes_[i][s] += cm.slot_bytes_[i][s];
      }
    }
  }
}

void CostModel::MergeFromStats(const NodeNameToCostIdMap& map,
                               const StepStats& ss) {
  CHECK(is_global_);
  for (auto& ds : ss.dev_stats()) {
    for (auto& ns : ds.node_stats()) {
      NodeNameToCostIdMap::const_iterator iter = map.find(ns.node_name());
      // We don't keep stats for nodes not in the global graph, i.e.
      // copy/send/recv nodes, feed/fetch, etc.
      if (iter == map.end()) continue;
      int32 global_id = iter->second;
      Ensure(global_id);
      int64 elapsed_micros = ns.op_end_rel_micros() - ns.op_start_rel_micros();
      count_[global_id]++;
      time_[global_id] += elapsed_micros;
      for (auto& no : ns.output()) {
        int si = no.slot();
        if (static_cast<size_t>(si) >= slot_bytes_[global_id].size()) {
          slot_bytes_[global_id].resize(1 + si);
        }
        slot_bytes_[global_id][si] +=
            no.tensor_description().allocation_description().requested_bytes();
      }
    }
  }
}

void CostModel::Ensure(int id) {
  if (slot_bytes_.size() <= static_cast<size_t>(id)) {
    slot_bytes_.resize(id + 1);
    count_.resize(id + 1);
    time_.resize(id + 1);
    max_mem_usage_.resize(id + 1);
    max_exec_time_.resize(id + 1);
    output_port_alias_.resize(id + 1);
  }
}

void CostModel::SetNumOutputs(const Node* node, int num_outputs) {
  const int id = Id(node);
  if (id < 0) return;
  Ensure(id);
  auto perslot = &slot_bytes_[id];
  auto max_mem_usage = &max_mem_usage_[id];
  auto output_port_alias = &output_port_alias_[id];
  if (perslot->size() > 0) {
    CHECK_EQ(num_outputs, perslot->size()) << "Cannot resize slot_bytes, node="
                                           << node->name();
  } else {
    perslot->resize(num_outputs, Bytes(-1));
    max_mem_usage->output_port_mem.resize(num_outputs, Bytes(-1));
    max_mem_usage->temp_memory_size = Bytes(-1);
    output_port_alias->resize(num_outputs, -1);
  }
}

void CostModel::RecordCount(const Node* node, int count) {
  const int id = Id(node);
  if (id < 0) return;
  CHECK_LT(id, slot_bytes_.size());
  count_[id] += count;
}

int32 CostModel::TotalCount(const Node* node) const {
  const int id = Id(node);
  if (id < 0) return 0;
  return (static_cast<size_t>(id) < slot_bytes_.size()) ? count_[id] : 0;
}

void CostModel::RecordSize(const Node* node, int slot, Bytes bytes) {
  const int id = Id(node);
  if (id < 0) return;
  CHECK_LT(id, slot_bytes_.size());
  auto perslot = &slot_bytes_[id];
  CHECK_LT(slot, perslot->size());
  auto v = &(*perslot)[slot];
  if (*v >= 0) {
    *v += bytes;
  } else {
    *v = bytes;
  }
}

Bytes CostModel::TotalBytes(const Node* node, int slot) const {
  const int id = Id(node);
  if (id < 0 || static_cast<size_t>(id) >= slot_bytes_.size() ||
      slot_bytes_[id].size() <= static_cast<size_t>(slot)) {
    return Bytes(0);
  }
  return slot_bytes_[id][slot];
}

Bytes CostModel::SizeEstimate(const Node* node, int slot) const {
  int32 count = TotalCount(node);
  if (count < min_count_) return Bytes(0);
  return TotalBytes(node, slot) / std::max(1, TotalCount(node));
}

void CostModel::RecordTime(const Node* node, Microseconds time) {
  const int id = Id(node);
  if (id < 0) return;
  DCHECK(node->IsOp()) << node->DebugString();
  Ensure(id);
  time_[id] += time;
}

Microseconds CostModel::TotalTime(const Node* node) const {
  DCHECK(node->IsOp()) << node->DebugString();
  const int id = Id(node);
  if (id < 0 || static_cast<size_t>(id) >= time_.size() ||
      time_[id] < Microseconds(0)) {
    return Microseconds(0);
  }
  return time_[id];
}

Microseconds CostModel::TimeEstimate(const Node* node) const {
  int32 count = TotalCount(node);
  if (count <= min_count_) return kMinTimeEstimate;
  return std::max(kMinTimeEstimate, TotalTime(node) / std::max(1, count));
}

void CostModel::CheckInitialized(const Graph& graph) const {
  for (const Node* n : graph.nodes()) {
    if (n->IsOp()) {
      CHECK(static_cast<size_t>(n->id()) < time_.size() &&
            time_[n->id()] >= Microseconds(0))
          << ": no time estimate for " << n->DebugString();

      CHECK(static_cast<size_t>(n->id()) < slot_bytes_.size())
          << ": no size estimate for " << n->DebugString();
      const auto& perslot = slot_bytes_[n->id()];
      for (size_t i = 0; i < perslot.size(); i++) {
        CHECK_GE(perslot[i], Bytes(0)) << ": no size estimate for output# " << i
                                       << " of " << n->DebugString();
      }
    }
  }
}

void CostModel::RecordMaxSize(const Node* node, int output_slot, Bytes bytes) {
  const int id = Id(node);
  if (id < 0) return;
  Ensure(id);
  max_mem_usage_[id].output_port_mem[output_slot] = bytes;
}

Bytes CostModel::MaxSize(const Node* node, int slot) const {
  const int id = Id(node);
  if (id < 0 || static_cast<size_t>(id) >= slot_bytes_.size() ||
      slot_bytes_[id].size() <= static_cast<size_t>(slot)) {
    return Bytes(0);
  }
  return max_mem_usage_[id].output_port_mem[slot];
}

void CostModel::RecordMaxExecutionTime(const Node* node, Microseconds time) {
  const int id = Id(node);
  if (id < 0) return;
  Ensure(id);
  max_exec_time_[id] = std::max(max_exec_time_[id], time);
}

Microseconds CostModel::MaxExecutionTime(const Node* node) const {
  const int id = Id(node);
  if (id < 0 || static_cast<size_t>(id) >= max_exec_time_.size()) {
    return Microseconds(0);
  }
  return max_exec_time_[id];
}

void CostModel::RecordAliases(const Node* node, int output_slot,
                              int64 alias_id) {
  const int id = Id(node);
  if (id < 0) return;
  Ensure(id);
  output_port_alias_[id][output_slot] = alias_id;
}

int64 CostModel::Aliases(const Node* node, int slot) const {
  const int id = Id(node);
  if (id < 0 || static_cast<size_t>(id) >= slot_bytes_.size() ||
      slot_bytes_[id].size() <= static_cast<size_t>(slot)) {
    return -1;
  }
  return output_port_alias_[id][slot];
}

Microseconds CostModel::CopyTimeEstimate(Bytes b, double network_latency_millis,
                                         double estimated_gbps) {
  // TODO(jeff,sanjay): estimate cost based on bandwidth along the
  // communication path and the type of transport we are using between
  // devices.
  //
  // We assume the copy time follows a linear model:
  //    copy_time = copy_bytes / rate + min_time
  int64 copy_bytes = b.value();
  const double bytes_per_usec = estimated_gbps * 1000.0 / 8;
  const double min_micros = network_latency_millis * 1000.0;
  return Microseconds(
      static_cast<int64>(copy_bytes / bytes_per_usec + min_micros));
}

Microseconds CostModel::ComputationTimeEstimate(int64 math_ops) {
  // TODO(jeff,sanjay): Eventually we should pass in the type of device
  // (GPU vs. CPU) and use that to affect the estimate.

  // We estimate the microseconds using that value.  We divide
  // by 1000 to convert the madd number into microseconds (assuming
  // roughly 1000 madds per microsecond (~1 GHz for one core)).
  return Microseconds(math_ops / 1000);
}

// ----------------------------------------------------------------------------
// InitCostModel
// ----------------------------------------------------------------------------

namespace {

static void AddNodesToCostModel(const Graph& g, CostModel* cost_model) {
  for (Node* n : g.nodes()) {
    const int num_outputs = n->num_outputs();
    cost_model->SetNumOutputs(n, num_outputs);
    for (int output = 0; output < num_outputs; output++) {
      // Set up an initial bogus estimate for the node's outputs
      cost_model->RecordSize(n, output, Bytes(1));
    }
  }
}

static void AssignSizes(const Graph& g, CostModel* cost_model) {
  for (const Edge* e : g.edges()) {
    // Skip if it is a control edge.
    if (e->IsControlEdge()) {
      continue;
    }
    Node* src = e->src();

    // TODO(josh11b): Get an estimate from the Op
    Bytes size(1);
    cost_model->RecordSize(src, e->src_output(), size);
  }
}

// This generates an extremely simple initial guess for the
// computation cost of each node. For ordinary Ops, its value should quickly
// be wiped out by the real runtime measurements.  For other Ops we don't
// actually generate measurements, so suppression of infrequent Ops ends up
// giving them 0 costs.  So, this is not of much consequence except perhaps
// in tests.
static Microseconds TimeEstimateForNode(CostModel* cost_model, Node* n) {
  CHECK(n->IsOp());
  VLOG(2) << "Node " << n->id() << ": " << n->name()
          << " type_string: " << n->type_string();
  if (IsConstant(n) || IsVariable(n)) {
    return Microseconds(0);
  }
  return kDefaultTimeEstimate;
}

static void EstimateComputationCosts(const Graph& g, CostModel* cost_model) {
  for (Node* n : g.nodes()) {
    if (!n->IsOp()) continue;
    cost_model->RecordTime(n, TimeEstimateForNode(cost_model, n));
  }
}

}  // namespace

void CostModel::InitFromGraph(const Graph& g) {
  AddNodesToCostModel(g, this);
  AssignSizes(g, this);
  EstimateComputationCosts(g, this);
  CheckInitialized(g);
}

void CostModel::WriteToLog() {
  LOG(INFO) << " min_count_=" << min_count_;
  for (size_t i = 0; i < count_.size(); ++i) {
    LOG(INFO) << "Node " << i << " count " << count_[i] << " total time "
              << time_[i] << " avg time "
              << (time_[i] / (std::max(1, count_[i])));
  }
}

}  // namespace tensorflow
