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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
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