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static: Various convergence improvements for ECP5
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Signed-off-by: gatecat <[email protected]>
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@gatecat
gatecat committed Jun 18, 2024
1 parent 61cc525 commit 945cf48
Showing 1 changed file with 126 additions and 58 deletions.
184 changes: 126 additions & 58 deletions common/place/placer_static.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -56,6 +56,7 @@ namespace {

struct PlacerGroup
{
bool enabled = true;
int total_bels = 0;
double concrete_area = 0;
double dark_area = 0;
Expand All @@ -70,6 +71,9 @@ struct PlacerGroup
FFTArray density_fft;
FFTArray electro_phi;
FFTArray electro_fx, electro_fy;

double init_potential = 0;
double curr_potential = 0;
};

// Could be an actual concrete netlist cell; or just a spacer
Expand Down Expand Up @@ -301,7 +305,7 @@ class StaticPlacer
dict<IdString, int> beltype2group;
for (int i = 0; i < int(groups.size()); i++) {
groups.at(i).loc_area.reset(width, height);
for (const auto &bel_type : cfg.cell_groups.at(i).cell_area)
for (const auto &bel_type : cfg.cell_groups.at(i).bel_area)
beltype2group[bel_type.first] = i;
}
for (auto bel : ctx->getBels()) {
Expand Down Expand Up @@ -409,14 +413,16 @@ class StaticPlacer
StaticRect rect;
// Mismatched group case
if (!lookup_group(ci->type, cell_group, rect)) {
for (auto bel : ctx->getBels()) {
if (ctx->isValidBelForCellType(ci->type, bel) && ctx->checkBelAvail(bel)) {
ctx->bindBel(bel, ci, STRENGTH_STRONG);
if (!ctx->isBelLocationValid(bel)) {
ctx->unbindBel(bel);
} else {
log_info(" placed potpourri cell '%s' at bel '%s'\n", ctx->nameOf(ci), ctx->nameOfBel(bel));
break;
if (ci->bel == BelId()) {
for (auto bel : ctx->getBels()) {
if (ctx->isValidBelForCellType(ci->type, bel) && ctx->checkBelAvail(bel)) {
ctx->bindBel(bel, ci, STRENGTH_STRONG);
if (!ctx->isBelLocationValid(bel)) {
ctx->unbindBel(bel);
} else {
log_info(" placed potpourri cell '%s' at bel '%s'\n", ctx->nameOf(ci), ctx->nameOfBel(bel));
break;
}
}
}
}
Expand Down Expand Up @@ -506,26 +512,31 @@ class StaticPlacer
}
}

const double target_util = 0.8;
const double target_util = 0.7;

void insert_dark()
{
log_info("⌁ inserting dark nodes...\n");
for (int group = 0; group < int(groups.size()); group++) {
const auto &cg = cfg.cell_groups.at(group);
auto &g = groups.at(group);
int dark_count = 0;
for (auto tile : g.loc_area) {
if (tile.value > 0.5f)
continue;
StaticRect dark_area(1.0f, 1.0f - tile.value);
int cell_idx = add_cell(dark_area, group, RealPair(tile.x + 0.5f, tile.y + 0.5f), nullptr /*spacer*/);
int cell_idx = add_cell(dark_area, group, RealPair(tile.x, tile.y), nullptr /*spacer*/);
mcells.at(cell_idx).is_dark = true;
++dark_count;
}
log_info("⌁ group %s inserted a total of %d dark nodes\n", ctx->nameOf(cg.name), dark_count);
}
}

void insert_spacer()
{
log_info("⌁ inserting spacers...\n");

int inserted_spacers = 0;
for (int group = 0; group < int(groups.size()); group++) {
const auto &cg = cfg.cell_groups.at(group);
Expand All @@ -537,8 +548,13 @@ class StaticPlacer
int spacer_count = (g.total_area * target_util - g.concrete_area) / cg.spacer_rect.area();
if (spacer_count <= 0)
continue;
for (int i = 0; i < spacer_count; i++) {
add_cell(cg.spacer_rect, group, RealPair(ctx->rngf(width), ctx->rngf(height)), nullptr /*spacer*/);
while (inserted_spacers < spacer_count) {
int x = ctx->rng(width);
int y = ctx->rng(height);
// avoid placing spacers at locations with dark nodes
if (ctx->rngf(1.0) > g.loc_area.at(x, y))
continue;
add_cell(cg.spacer_rect, group, RealPair(x + ctx->rngf(1.0), y + ctx->rngf(1.0)), nullptr /*spacer*/);
++inserted_spacers;
}
}
Expand All @@ -556,7 +572,7 @@ class StaticPlacer
{
// TODO: a m x m grid follows the paper and makes the DCTs easier, but is it actually ideal for non-square
// FPGAs?
m = 1 << int(std::ceil(std::log2(std::sqrt(mcells.size() / groups.size()))));
m = 1 << int(std::ceil(std::log2(std::max(width, height))));
bin_w = double(width) / m;
bin_h = double(height) / m;

Expand Down Expand Up @@ -591,18 +607,18 @@ class StaticPlacer
double y0 = pos.y, y1 = pos.y + height;
for (int y = int(y0 / bin_h); y <= int(y1 / bin_h); y++) {
for (int x = int(x0 / bin_w); x <= int(x1 / bin_w); x++) {
int xb = std::max(0, std::min(x, m - 1));
int yb = std::max(0, std::min(y, m - 1));
if (x < 0 || x >= m || y < 0 || y >= m)
continue;
double slither_w = 1.0, slither_h = 1.0;
if (yb == int(y0 / bin_h)) // y slithers
slither_h = ((yb + 1) * bin_h) - y0;
else if (yb == int(y1 / bin_h))
slither_h = (y1 - yb * bin_h);
if (xb == int(x0 / bin_w)) // x slithers
slither_w = ((xb + 1) * bin_w) - x0;
else if (xb == int(x1 / bin_w))
slither_w = (x1 - xb * bin_w);
func(xb, yb, scaled_density * slither_w * slither_h);
if (y == int(y0 / bin_h)) // y slithers
slither_h = ((y + 1) * bin_h) - y0;
else if (y == int(y1 / bin_h))
slither_h = (y1 - y * bin_h);
if (x == int(x0 / bin_w)) // x slithers
slither_w = ((x + 1) * bin_w) - x0;
else if (x == int(x1 / bin_w))
slither_w = (x1 - x * bin_w);
func(x, y, scaled_density * slither_w * slither_h);
}
}
};
Expand All @@ -626,11 +642,10 @@ class StaticPlacer
}
}

void compute_overlap()
void compute_conc_density()
{
// populate for concrete cells only
for (auto &g : groups)
g.conc_density.reset(m, m, 0);
g.conc_density.reset(width, height, 0);
for (int idx = 0; idx < int(ccells.size()); idx++) {
auto &mc = mcells.at(idx);
auto &g = groups.at(mc.group);
Expand All @@ -641,10 +656,18 @@ class StaticPlacer
for (int dx = 0; dx <= int(size.w); dx++) {
float h = (dy == int(size.h)) ? (size.h - int(size.h)) : 1;
float w = (dx == int(size.w)) ? (size.w - int(size.w)) : 1;
g.conc_density.at(loc.x + dx, loc.y + dy) += w * h;
if ((loc.x + dx) >= 0 && (loc.x + dx) < width && (loc.y + dy) >= 0 && (loc.y + dy) < height)
g.conc_density.at(loc.x + dx, loc.y + dy) += w * h;
}
}
}
}

void compute_overlap()
{
// populate for concrete cells only
compute_conc_density();

std::string overlap_str = "";
for (int idx = 0; idx < int(groups.size()); idx++) {
auto &g = groups.at(idx);
Expand All @@ -671,7 +694,7 @@ class StaticPlacer
auto &g = groups.at(group);
for (auto entry : g.density)
g.density_fft.at(entry.x, entry.y) = entry.value;
if (fft_debug)
if (fft_debug || dump_density)
g.density_fft.write_csv(stringf("out_bin_density_%d_%d.csv", iter, group));
// Based on
// https://github.com/ALIGN-analoglayout/ALIGN-public/blob/master/PlaceRouteHierFlow/EA_placer/FFT/fft.cpp
Expand Down Expand Up @@ -736,7 +759,7 @@ class StaticPlacer

void update_nets(bool ref)
{
static constexpr float min_wirelen_force = -300.f;
static constexpr float min_wirelen_force = -3000.f;
pool.run(2 * nets.size(), [&](int i) {
auto &net = nets.at(i / 2);
auto axis = (i % 2) ? Axis::Y : Axis::X;
Expand Down Expand Up @@ -868,28 +891,17 @@ class StaticPlacer
}
if (init_penalty) {
// set initial density penalty
dict<int, float> wirelen_sum;
dict<int, float> force_sum;
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]);
double wirelen_sum = 0, force_sum = 0;
for (int i = 0; i < int(ccells.size()); i++) {
auto mc = mcells.at(i);
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-1;
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 @@ -953,17 +965,59 @@ 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.init_potential = group.curr_potential;
}
}

float system_potential()
{
float pot = 0;
for (auto &group : groups)
pot += group.curr_potential;
return pot;
}

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.init_potential;
rel_pot.push_back(phi_hat);
pot_norm += phi_hat * phi_hat;
}
pot_norm = sqrt(pot_norm);
log_info("pot_norm: %f\n", 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 initialise()
{
float initial_steplength = 0.01f;
Expand Down Expand Up @@ -1016,6 +1070,7 @@ class StaticPlacer
// Move the post-solve position of a chain towards be the weighted average of its constituents
// The strength increases with iterations
float alpha = std::min<float>(std::pow(1.002f, iter) - 1, 1.0f);
float dist = 0;
for (int i = 0; i < int(macros.size()); i++) {
auto &macro = macros.at(i);
float total_area = 0;
Expand All @@ -1033,10 +1088,13 @@ class StaticPlacer
for (int c : macro.conc_cells) {
auto &cc = ccells.at(c);
auto &mc = mcells.at(c);
auto last_pos = mc.pos;
mc.pos = mc.pos * (1 - alpha) + (pos + RealPair(cc.chunk_dx, cc.chunk_dy)) * alpha;
mc.ref_pos = mc.ref_pos * (1 - alpha) + (ref_pos + RealPair(cc.chunk_dx, cc.chunk_dy)) * alpha;
dist += std::sqrt(std::pow(last_pos.x - mc.pos.x, 2) + std::pow(last_pos.y - mc.pos.y, 2));
}
}
log_info(" update_chains distance %.2f\n", dist);
}

void step()
Expand Down Expand Up @@ -1064,9 +1122,10 @@ 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();
if ((iter % 5) == 0)
if ((iter % 10) == 0)
update_timing();
}

Expand Down Expand Up @@ -1410,15 +1469,24 @@ class StaticPlacer
bool legalised_ip = false;
while (true) {
step();
for (auto &penalty : dens_penalty)
penalty *= 1.025;
for (auto &p : dens_penalty)
if (p < 50.0)
p *= 1.025;
else
p += 1.0;
// wl_coeff.at(Axis::X) = std::max(0.005, 0.995 * wl_coeff.at(Axis::X));
// wl_coeff.at(Axis::Y) = std::max(0.005, 0.995 * wl_coeff.at(Axis::Y));

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

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