1 files changed, 99 insertions, 0 deletions
diff --git a/intern/cycles/integrator/work_balancer.cpp b/intern/cycles/integrator/work_balancer.cpp
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index 00000000000..9f96fe3632b
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+++ b/intern/cycles/integrator/work_balancer.cpp
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+/*
+ * Copyright 2011-2021 Blender Foundation
+ *
+ * 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 "integrator/work_balancer.h"
+
+#include "util/util_math.h"
+
+#include "util/util_logging.h"
+
+CCL_NAMESPACE_BEGIN
+
+void work_balance_do_initial(vector<WorkBalanceInfo> &work_balance_infos)
+{
+  const int num_infos = work_balance_infos.size();
+
+  if (num_infos == 1) {
+    work_balance_infos[0].weight = 1.0;
+    return;
+  }
+
+  /* There is no statistics available, so start with an equal distribution. */
+  const double weight = 1.0 / num_infos;
+  for (WorkBalanceInfo &balance_info : work_balance_infos) {
+    balance_info.weight = weight;
+  }
+}
+
+static double calculate_total_time(const vector<WorkBalanceInfo> &work_balance_infos)
+{
+  double total_time = 0;
+  for (const WorkBalanceInfo &info : work_balance_infos) {
+    total_time += info.time_spent;
+  }
+  return total_time;
+}
+
+/* The balance is based on equalizing time which devices spent performing a task. Assume that
+ * average of the observed times is usable for estimating whether more or less work is to be
+ * scheduled, and how difference in the work scheduling is needed. */
+
+bool work_balance_do_rebalance(vector<WorkBalanceInfo> &work_balance_infos)
+{
+  const int num_infos = work_balance_infos.size();
+
+  const double total_time = calculate_total_time(work_balance_infos);
+  const double time_average = total_time / num_infos;
+
+  double total_weight = 0;
+  vector<double> new_weights;
+  new_weights.reserve(num_infos);
+
+  /* Equalize the overall average time. This means that we don't make it so every work will perform
+   * amount of work based on the current average, but that after the weights changes the time will
+   * equalize.
+   * Can think of it that if one of the devices is 10% faster than another, then one device needs
+   * to do 5% less of the current work, and another needs to do 5% more. */
+  const double lerp_weight = 1.0 / num_infos;
+
+  bool has_big_difference = false;
+
+  for (const WorkBalanceInfo &info : work_balance_infos) {
+    const double time_target = lerp(info.time_spent, time_average, lerp_weight);
+    const double new_weight = info.weight * time_target / info.time_spent;
+    new_weights.push_back(new_weight);
+    total_weight += new_weight;
+
+    if (std::fabs(1.0 - time_target / time_average) > 0.02) {
+      has_big_difference = true;
+    }
+  }
+
+  if (!has_big_difference) {
+    return false;
+  }
+
+  const double total_weight_inv = 1.0 / total_weight;
+  for (int i = 0; i < num_infos; ++i) {
+    WorkBalanceInfo &info = work_balance_infos[i];
+    info.weight = new_weights[i] * total_weight_inv;
+    info.time_spent = 0;
+  }
+
+  return true;
+}
+
+CCL_NAMESPACE_END