Differential D12367 Diff 41308 intern/cycles/integrator/work_balancer.cpp

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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