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static: Improving penalty calculation
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Signed-off-by: gatecat <[email protected]>
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@gatecat
gatecat committed Nov 25, 2023
1 parent e3f4578 commit 87a9c7c
Showing 1 changed file with 72 additions and 25 deletions.
97 changes: 72 additions & 25 deletions common/place/placer_static.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -48,6 +48,7 @@ namespace {

struct PlacerGroup
{
bool enabled = true;
int total_bels = 0;
double concrete_area = 0;
double dark_area = 0;
Expand All @@ -62,6 +63,9 @@ struct PlacerGroup
FFTArray density_fft;
FFTArray electro_phi;
FFTArray electro_fx, electro_fy;
// potential energy
float initial_potential = 0;
float curr_potential = 0;
};

// Could be an actual concrete netlist cell; or just a spacer
Expand Down Expand Up @@ -750,28 +754,20 @@ class StaticPlacer
}
if (init_penalty) {
// set initial density penalty
dict<int, float> wirelen_sum;
dict<int, float> force_sum;
float wirelen_sum = 0, force_sum = 0;
for (auto &cell : ctx->cells) {
CellInfo *ci = cell.second.get();
if (ci->udata == -1)
continue;
auto &mc = mcells.at(ci->udata);
auto res1 = wirelen_sum.insert({mc.group, std::abs(mc.ref_wl_grad.x) + std::abs(mc.ref_wl_grad.y)});
if (!res1.second)
res1.first->second += std::abs(mc.ref_wl_grad.x) + std::abs(mc.ref_wl_grad.y);
auto res2 = force_sum.insert({mc.group, std::abs(mc.ref_dens_grad.x) + std::abs(mc.ref_dens_grad.y)});
if (!res2.second)
res2.first->second += std::abs(mc.ref_dens_grad.x) + std::abs(mc.ref_dens_grad.y);
}
dens_penalty = std::vector<float>(wirelen_sum.size(), 0.0);
for (auto &item : wirelen_sum) {
auto group = item.first;
auto wirelen = item.second;
dens_penalty[group] = wirelen / force_sum.at(group);
log_info(" initial density penalty for %s: %f\n", cfg.cell_groups.at(group).name.c_str(ctx),
dens_penalty[group]);
wirelen_sum += std::abs(mc.ref_wl_grad.x) + std::abs(mc.ref_wl_grad.y);
force_sum += std::abs(mc.ref_dens_grad.x) + std::abs(mc.ref_dens_grad.y);
}
const float eta = 1e-4;
float init_dens_penalty = eta * (wirelen_sum / force_sum);
log_info("initial density penalty: %f\n", init_dens_penalty);
dens_penalty.resize(groups.size(), init_dens_penalty);
update_potentials(true); // set initial potential
}
// Third loop: compute total gradient, and precondition
// TODO: ALM as well as simple penalty
Expand Down Expand Up @@ -834,13 +830,28 @@ class StaticPlacer
return hpwl;
}

float system_potential()
void update_potentials(bool init = false)
{
float pot = 0;
for (auto &group : groups) {
group.curr_potential = 0;
}
for (auto &cell : mcells) {
auto &g = groups.at(cell.group);
iter_slithers(cell.ref_pos, cell.rect,
[&](int x, int y, float area) { pot += g.electro_phi.at(x, y) * area; });
[&](int x, int y, float area) { g.curr_potential += g.electro_phi.at(x, y) * area; });
}
if (init) {
for (auto &group : groups) {
group.initial_potential = group.curr_potential;
}
}
}

float system_potential()
{
float pot = 0;
for (auto &group : groups) {
pot += group.curr_potential;
}
return pot;
}
Expand Down Expand Up @@ -917,6 +928,35 @@ class StaticPlacer
}
}

float penalty_beta = 2.0e3f;
float alpha_l = 1.05f, alpha_h = 1.06f;
double penalty_incr = alpha_h - 1;

void update_penalties() {
float pot_norm = 0;
// compute L2-norm of relative system potential
std::vector<float> rel_pot;
for (int g = 0; g < int(groups.size()); g++) {
auto &group = groups.at(g);
if (!group.enabled)
continue;
float phi_hat = group.curr_potential / group.initial_potential;
rel_pot.push_back(phi_hat);
pot_norm += phi_hat * phi_hat;
}
pot_norm = sqrt(pot_norm);
// update penalty multiplier (ELFPlace equation 22)
double log_term = std::log(penalty_beta * pot_norm + 1);
penalty_incr = penalty_incr * ((log_term / (log_term + 1)) * (alpha_h - alpha_l) + alpha_l);
// update density penalties (ELFPlace equation 21)
for (int g = 0; g < int(groups.size()); g++) {
if (!groups.at(g).enabled)
continue;
float next_penalty = dens_penalty.at(g) + (penalty_incr * (rel_pot.at(g) / pot_norm));
dens_penalty.at(g) = next_penalty;
}
}

void step()
{
// TODO: update penalties; wirelength factor; etc
Expand All @@ -938,6 +978,7 @@ class StaticPlacer
nesterov_a = a_next;
update_chains();
update_gradients(true);
update_potentials();
log_info(" system potential: %f hpwl: %f\n", system_potential(), system_hpwl());
compute_overlap();
}
Expand Down Expand Up @@ -1245,6 +1286,7 @@ class StaticPlacer
}
}


public:
StaticPlacer(Context *ctx, PlacerStaticCfg cfg) : ctx(ctx), cfg(cfg), fast_bels(ctx, true, 8), tmg(ctx)
{
Expand All @@ -1265,20 +1307,25 @@ class StaticPlacer
bool legalised_ip = false;
while (true) {
step();
for (auto &penalty : dens_penalty)
penalty *= 1.025;
// for (auto &penalty : dens_penalty)
// penalty *= 1.025;
update_penalties();

float logic_overlap = 0;
for (int i = 0; i < 2; i++)
logic_overlap = std::max(logic_overlap, groups.at(i).overlap);

if (!legalised_ip) {
float ip_overlap = 0;
for (int i = 2; i < int(groups.size()); i++)
ip_overlap = std::max(ip_overlap, groups.at(i).overlap);
if (ip_overlap < 0.15) {
if (logic_overlap < 0.15 && ip_overlap < 0.15) {
legalise_step(true);
legalised_ip = true;
for (int i = 2; i < int(groups.size()); i++)
groups.at(i).enabled = false;
}
} else {
float logic_overlap = 0;
for (int i = 0; i < 2; i++)
logic_overlap = std::max(logic_overlap, groups.at(i).overlap);
if (logic_overlap < 0.1) {
legalise_step(false);
break;
Expand Down

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