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[Place] Added an Initial Placement Checkpoint #3233

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[Place] Added an Initial Placement Checkpoint #3233

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12 changes: 12 additions & 0 deletions vpr/src/place/place_checkpoint.cpp
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Original file line number Diff line number Diff line change
@@ -1,11 +1,13 @@

#include "place_checkpoint.h"

#include "net_cost_handler.h"
#include "noc_place_utils.h"
#include "placer_state.h"
#include "grid_block.h"
#include "PlacerCriticalities.h"
#include "PlacerSetupSlacks.h"
#include "vpr_types.h"

float t_placement_checkpoint::get_cp_cpd() const { return cpd_; }

Expand Down Expand Up @@ -49,6 +51,9 @@ void restore_best_placement(PlacerState& placer_state,
std::shared_ptr<PlaceDelayModel>& place_delay_model,
std::unique_ptr<NetPinTimingInvalidator>& pin_timing_invalidator,
PlaceCritParams crit_params,
NetCostHandler& net_cost_handler,
const t_placer_opts& placer_opts,
const t_noc_opts& noc_opts,
std::optional<NocCostHandler>& noc_cost_handler) {
/* The (valid) checkpoint is restored if the following conditions are met:
* 1) The checkpoint has a lower critical path delay.
Expand All @@ -73,6 +78,13 @@ void restore_best_placement(PlacerState& placer_state,
&costs,
placer_state);

// Recompute the wirelength cost terms from scratch.
costs.bb_cost = net_cost_handler.comp_bb_cost(e_cost_methods::NORMAL).first;

// Update the normalization factors and recompute the total cost.
costs.update_norm_factors();
costs.cost = costs.get_total_cost(placer_opts, noc_opts);

/* If NoC is enabled, re-compute NoC costs and re-initialize NoC internal data structures.
* If some routers have different locations than the last placement, NoC-related costs and
* internal data structures that are used to keep track of each flow's cost are no longer valid,
Expand Down
4 changes: 4 additions & 0 deletions vpr/src/place/place_checkpoint.h
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Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,7 @@
#include "place_delay_model.h"
#include "place_timing_update.h"

class NetCostHandler;
class NocCostHandler;

/**
Expand Down Expand Up @@ -74,4 +75,7 @@ void restore_best_placement(PlacerState& placer_state,
std::shared_ptr<PlaceDelayModel>& place_delay_model,
std::unique_ptr<NetPinTimingInvalidator>& pin_timing_invalidator,
PlaceCritParams crit_params,
NetCostHandler& net_cost_handler,
const t_placer_opts& placer_opts,
const t_noc_opts& noc_opts,
std::optional<NocCostHandler>& noc_cost_handler);
52 changes: 46 additions & 6 deletions vpr/src/place/placer.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -286,6 +286,19 @@ void Placer::place() {
// Table header
log_printer_.print_place_status_header();

// Save a checkpoint of the initial placement. This may be restored
// during the anneal (or rarely at the end of anneal) if it is found to
// have a better quality than the current placement solution.
bool checkpoint_is_initial_placement = false;
if (placer_opts_.place_algorithm.is_timing_driven()) {
critical_path_ = timing_info_->least_slack_critical_path();
save_placement_checkpoint_if_needed(placer_state_.mutable_block_locs(),
placement_checkpoint_,
timing_info_, costs_, critical_path_.delay());
checkpoint_is_initial_placement = true;
}

unsigned num_outer_loop_iterations = 0;
// Outer loop of the simulated annealing begins
do {
vtr::Timer temperature_timer;
Expand All @@ -295,11 +308,33 @@ void Placer::place() {
if (placer_opts_.place_algorithm.is_timing_driven()) {
critical_path_ = timing_info_->least_slack_critical_path();

// see if we should save the current placement solution as a checkpoint
if (placer_opts_.place_checkpointing && annealer_->get_agent_state() == e_agent_state::LATE_IN_THE_ANNEAL) {
save_placement_checkpoint_if_needed(placer_state_.mutable_block_locs(),
placement_checkpoint_,
timing_info_, costs_, critical_path_.delay());
// If place checkpointing is on, depending on the current state
// of the anneal, we should see if we should save the current
// placement solution as a checkpoint or restore it.
if (placer_opts_.place_checkpointing) {
if (checkpoint_is_initial_placement && num_outer_loop_iterations == 20) {
// If the checkpoint currently saved is the intial placement,
// after 20 iterations of the outer loop, if the quality is
// worse we should restore to that initial placement solution.
const t_annealing_state& annealing_state = annealer_->get_annealing_state();
PlaceCritParams crit_params;
crit_params.crit_exponent = annealing_state.crit_exponent;
crit_params.crit_limit = placer_opts_.place_crit_limit;
restore_best_placement(placer_state_,
placement_checkpoint_, timing_info_, costs_,
placer_criticalities_, placer_setup_slacks_, place_delay_model_,
pin_timing_invalidator_, crit_params,
net_cost_handler_,
placer_opts_, noc_opts_,
noc_cost_handler_);
} else if (annealer_->get_agent_state() == e_agent_state::LATE_IN_THE_ANNEAL) {
// If we are late in the anneal, we should try and create a
// checkpoint if needed.
save_placement_checkpoint_if_needed(placer_state_.mutable_block_locs(),
placement_checkpoint_,
timing_info_, costs_, critical_path_.delay());
checkpoint_is_initial_placement = false;
}
}
}

Expand All @@ -308,6 +343,8 @@ void Placer::place() {

log_printer_.print_place_status(temperature_timer.elapsed_sec());

num_outer_loop_iterations++;

// Outer loop of the simulated annealing ends
} while (annealer_->outer_loop_update_state());
} // skip_anneal ends
Expand Down Expand Up @@ -355,7 +392,10 @@ void Placer::place() {
restore_best_placement(placer_state_,
placement_checkpoint_, timing_info_, costs_,
placer_criticalities_, placer_setup_slacks_, place_delay_model_,
pin_timing_invalidator_, crit_params, noc_cost_handler_);
pin_timing_invalidator_, crit_params,
net_cost_handler_,
placer_opts_, noc_opts_,
noc_cost_handler_);
}

if (placer_opts_.placement_saves_per_temperature >= 1) {
Expand Down