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Linkgraph: Dynamically adjust accuracy parameters in MCF 1st pass

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For larger graphs (>= 50 nodes), reduce the accuracy and set a
minimum push flow threshold.
This avoids wasting a lot of time calculating very small flow demand
increments when the total number of demands is high and most demands
are small already.
This commit is contained in:
Jonathan G Rennison
2022-12-07 02:24:17 +00:00
parent 351090ae7f
commit ad815210ae
2 changed files with 26 additions and 6 deletions
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30
src/linkgraph/mcf.cpp
View File

@@ -393,15 +393,16 @@ void MultiCommodityFlow::CleanupPaths(NodeID source_id, PathVector &paths)
* edge.
* @param edge Edge whose ends the path connects.
* @param path End of the path the flow should be pushed on.
* @param min_step_size Minimum flow size.
* @param accuracy Accuracy of the calculation.
* @param max_saturation If < UINT_MAX only push flow up to the given
* saturation, otherwise the path can be "overloaded".
*/
uint MultiCommodityFlow::PushFlow(AnnoEdge &edge, Path *path, uint accuracy,
uint MultiCommodityFlow::PushFlow(AnnoEdge &edge, Path *path, uint min_step_size, uint accuracy,
uint max_saturation)
{
assert(edge.UnsatisfiedDemand() > 0);
uint flow = Clamp(edge.Demand() / accuracy, 1, edge.UnsatisfiedDemand());
uint flow = std::min(std::max(edge.Demand() / accuracy, min_step_size), edge.UnsatisfiedDemand());
flow = path->AddFlow(flow, this->job, max_saturation);
edge.SatisfyDemand(flow);
return flow;
@@ -564,6 +565,25 @@ MCF1stPass::MCF1stPass(LinkGraphJob &job) : MultiCommodityFlow(job)
bool more_loops;
std::vector<bool> finished_sources(size);
uint min_step_size = 1;
const uint adjust_threshold = 50;
if (size >= adjust_threshold) {
uint64 total_demand = 0;
uint demand_count = 0;
for (NodeID source = 0; source < size; ++source) {
for (NodeID dest = 0; dest < size; ++dest) {
AnnoEdge edge = job[source][dest];
if (edge.UnsatisfiedDemand() > 0) {
total_demand += edge.UnsatisfiedDemand();
demand_count++;
}
}
}
if (demand_count == 0) return;
min_step_size = std::max<uint>(min_step_size, (total_demand * (1 + FindLastBit(size / adjust_threshold))) / (size * accuracy));
accuracy = Clamp(IntSqrt((4 * accuracy * accuracy * size) / demand_count), CeilDiv(accuracy, 4), accuracy);
}
do {
more_loops = false;
for (NodeID source = 0; source < size; ++source) {
@@ -582,13 +602,13 @@ MCF1stPass::MCF1stPass(LinkGraphJob &job) : MultiCommodityFlow(job)
* available capacity. But if no demand has been assigned
* yet, make an exception and allow any valid path *once*. */
if (path->GetFreeCapacity() > 0 && this->PushFlow(edge, path,
accuracy, this->max_saturation) > 0) {
min_step_size, accuracy, this->max_saturation) > 0) {
/* If a path has been found there is a chance we can
* find more. */
more_loops = more_loops || (edge.UnsatisfiedDemand() > 0);
} else if (edge.UnsatisfiedDemand() == edge.Demand() &&
path->GetFreeCapacity() > INT_MIN) {
this->PushFlow(edge, path, accuracy, UINT_MAX);
this->PushFlow(edge, path, min_step_size, accuracy, UINT_MAX);
}
if (edge.UnsatisfiedDemand() > 0) source_demand_left = true;
}
@@ -624,7 +644,7 @@ MCF2ndPass::MCF2ndPass(LinkGraphJob &job) : MultiCommodityFlow(job)
AnnoEdge edge = this->job[source][dest];
Path *path = paths[dest];
if (edge.UnsatisfiedDemand() > 0 && path->GetFreeCapacity() > INT_MIN) {
this->PushFlow(edge, path, accuracy, UINT_MAX);
this->PushFlow(edge, path, 1, accuracy, UINT_MAX);
if (edge.UnsatisfiedDemand() > 0) {
demand_left = true;
source_demand_left = true;

2
src/linkgraph/mcf.h
View File

@@ -24,7 +24,7 @@ protected:
template<class Tannotation, class Tedge_iterator>
void Dijkstra(NodeID from, PathVector &paths);
uint PushFlow(AnnoEdge &edge, Path *path, uint accuracy, uint max_saturation);
uint PushFlow(AnnoEdge &edge, Path *path, uint min_step_size, uint accuracy, uint max_saturation);
void CleanupPaths(NodeID source, PathVector &paths);