embedded3 S2-2b: the moving path's host work 5.0 s → 0.6 s per step at 1.45 M cells, bit-identical — Problem::diagonals (the per-cell link diagonal was cells × links: 1.8 s twice per step), counting CSR + rayon in the device tables, rayon in the cut geometry builder; RTX_E3_MOVING_PROFILE laps

Co-Authored-By: Claude Fable 5.1 <[email protected]>

crates/specialized/rtx-cfd/src/solvers/incompressible/embedded3/cut.rs

@@ -59,26 +59,32 @@ impl CutGeometry {
         let g = grid;
         let (nx, ny, nz, dx, dy, dz) = (g.nx, g.ny, g.nz, g.dx, g.dy, g.dz);
         let n_nodes = (nx + 1) * (ny + 1) * (nz + 1);
+        // Every loop below is per-index with read-only inputs: rayon (S2-2b),
+        // the same arithmetic per entry.
+        use rayon::prelude::*;
         let mut phi = vec![0.0; n_nodes];
         let mut bound = vec![0.0; n_nodes];
-        for k in 0..=nz {
-            for j in 0..=ny {
-                for i in 0..=nx {
-                    let n = Self::node(g, k, j, i);
-                    if let Some((p, band, motion)) = prev {
-                        let b = p.bound[n] - motion;
-                        if b > band {
-                            phi[n] = p.phi[n];
-                            bound[n] = b;
-                            continue;
-                        }
+        phi.par_iter_mut()
+            .zip(bound.par_iter_mut())
+            .enumerate()
+            .for_each(|(n, (phi_n, bound_n))| {
+                let (k, j, i) = (
+                    n / ((ny + 1) * (nx + 1)),
+                    (n / (nx + 1)) % (ny + 1),
+                    n % (nx + 1),
+                );
+                if let Some((p, band, motion)) = prev {
+                    let b = p.bound[n] - motion;
+                    if b > band {
+                        *phi_n = p.phi[n];
+                        *bound_n = b;
+                        return;
                     }
-                    let v = body.phi(i as f64 * dx, j as f64 * dy, k as f64 * dz, t);
-                    phi[n] = v;
-                    bound[n] = v.abs();
                 }
-            }
-        }
+                let v = body.phi(i as f64 * dx, j as f64 * dy, k as f64 * dz, t);
+                *phi_n = v;
+                *bound_n = v.abs();
+            });
         let corner = |k: usize, j: usize, i: usize| phi[Self::node(g, k, j, i)];
         // Face apertures: a face's two triangles along the diagonal from its
         // (0, 0) to its (1, 1) corner in the face's own (a, b) order — the
@@ -113,51 +119,51 @@ impl CutGeometry {
         let mut d_u = vec![0.0; (nx + 1) * ny * nz];
         let mut d_v = vec![0.0; nx * (ny + 1) * nz];
         let mut d_w = vec![0.0; nx * ny * (nz + 1)];
-        for k in 0..nz {
-            for j in 0..ny {
-                for i in 0..=nx {
-                    // x-face at i: corners (j, k), (j+1, k), (j, k+1), (j+1, k+1)
-                    let (q00, q10, q01, q11) = (
-                        corner(k, j, i),
-                        corner(k, j + 1, i),
-                        corner(k + 1, j, i),
-                        corner(k + 1, j + 1, i),
-                    );
-                    a_u[g.uface(k, j, i)] = quad_fraction(q00, q10, q01, q11);
-                    d_u[g.uface(k, j, i)] = 0.25 * (q00 + q10 + q01 + q11);
-                }
-            }
-        }
-        for k in 0..nz {
-            for j in 0..=ny {
-                for i in 0..nx {
-                    // y-face at j: corners (i, k), (i+1, k), (i, k+1), (i+1, k+1)
-                    let (q00, q10, q01, q11) = (
-                        corner(k, j, i),
-                        corner(k, j, i + 1),
-                        corner(k + 1, j, i),
-                        corner(k + 1, j, i + 1),
-                    );
-                    a_v[g.vface(k, j, i)] = quad_fraction(q00, q10, q01, q11);
-                    d_v[g.vface(k, j, i)] = 0.25 * (q00 + q10 + q01 + q11);
-                }
-            }
-        }
-        for k in 0..=nz {
-            for j in 0..ny {
-                for i in 0..nx {
-                    // z-face at k: corners (i, j), (i+1, j), (i, j+1), (i+1, j+1)
-                    let (q00, q10, q01, q11) = (
-                        corner(k, j, i),
-                        corner(k, j, i + 1),
-                        corner(k, j + 1, i),
-                        corner(k, j + 1, i + 1),
-                    );
-                    a_w[g.wface(k, j, i)] = quad_fraction(q00, q10, q01, q11);
-                    d_w[g.wface(k, j, i)] = 0.25 * (q00 + q10 + q01 + q11);
-                }
-            }
-        }
+        a_u.par_iter_mut()
+            .zip(d_u.par_iter_mut())
+            .enumerate()
+            .for_each(|(f, (a, d))| {
+                // x-face at i: corners (j, k), (j+1, k), (j, k+1), (j+1, k+1)
+                let (k, j, i) = (f / (ny * (nx + 1)), (f / (nx + 1)) % ny, f % (nx + 1));
+                let (q00, q10, q01, q11) = (
+                    corner(k, j, i),
+                    corner(k, j + 1, i),
+                    corner(k + 1, j, i),
+                    corner(k + 1, j + 1, i),
+                );
+                *a = quad_fraction(q00, q10, q01, q11);
+                *d = 0.25 * (q00 + q10 + q01 + q11);
+            });
+        a_v.par_iter_mut()
+            .zip(d_v.par_iter_mut())
+            .enumerate()
+            .for_each(|(f, (a, d))| {
+                // y-face at j: corners (i, k), (i+1, k), (i, k+1), (i+1, k+1)
+                let (k, j, i) = (f / ((ny + 1) * nx), (f / nx) % (ny + 1), f % nx);
+                let (q00, q10, q01, q11) = (
+                    corner(k, j, i),
+                    corner(k, j, i + 1),
+                    corner(k + 1, j, i),
+                    corner(k + 1, j, i + 1),
+                );
+                *a = quad_fraction(q00, q10, q01, q11);
+                *d = 0.25 * (q00 + q10 + q01 + q11);
+            });
+        a_w.par_iter_mut()
+            .zip(d_w.par_iter_mut())
+            .enumerate()
+            .for_each(|(f, (a, d))| {
+                // z-face at k: corners (i, j), (i+1, j), (i, j+1), (i+1, j+1)
+                let (k, j, i) = (f / (ny * nx), (f / nx) % ny, f % nx);
+                let (q00, q10, q01, q11) = (
+                    corner(k, j, i),
+                    corner(k, j, i + 1),
+                    corner(k, j + 1, i),
+                    corner(k, j + 1, i + 1),
+                );
+                *a = quad_fraction(q00, q10, q01, q11);
+                *d = 0.25 * (q00 + q10 + q01 + q11);
+            });
         // Cell volumes by the Kuhn split: the six tetrahedra around the
         // diagonal (0,0,0)–(1,1,1) in unit-cube coordinates.
         let mut vol = vec![0.0; g.cells()];
@@ -170,36 +176,36 @@ impl CutGeometry {
             [[0, 0, 0], [0, 0, 1], [1, 0, 1], [1, 1, 1]],
             [[0, 0, 0], [0, 0, 1], [0, 1, 1], [1, 1, 1]],
         ];
-        for k in 0..nz {
-            for j in 0..ny {
-                for i in 0..nx {
-                    let mut fluid = 0.0;
-                    for tet in &KUHN {
-                        let pts: Vec<[f64; 3]> = tet
-                            .iter()
-                            .map(|c| [c[0] as f64, c[1] as f64, c[2] as f64])
-                            .collect();
-                        let vals: Vec<f64> = tet
-                            .iter()
-                            .map(|c| corner(k + c[2], j + c[1], i + c[0]))
-                            .collect();
-                        fluid += tet_fluid_volume(&pts, &vals);
-                    }
-                    // The six tets fill the unit cube (volume 1).
-                    let idx = g.cell(k, j, i);
-                    vol[idx] = fluid;
-                    let ax = dy * dz;
-                    let ay = dx * dz;
-                    let az = dx * dy;
-                    // Outward normals of the cell's faces times their fluid area,
-                    // summed; the wall closes the fluid part of the cell.
-                    let sx = (a_u[g.uface(k, j, i + 1)] - a_u[g.uface(k, j, i)]) * ax;
-                    let sy = (a_v[g.vface(k, j + 1, i)] - a_v[g.vface(k, j, i)]) * ay;
-                    let sz = (a_w[g.wface(k + 1, j, i)] - a_w[g.wface(k, j, i)]) * az;
-                    wall[idx] = [-sx, -sy, -sz];
-                }
+        let cell_fluid = |k: usize, j: usize, i: usize| -> f64 {
+            let mut fluid = 0.0;
+            for tet in &KUHN {
+                let pts: Vec<[f64; 3]> = tet
+                    .iter()
+                    .map(|c| [c[0] as f64, c[1] as f64, c[2] as f64])
+                    .collect();
+                let vals: Vec<f64> = tet
+                    .iter()
+                    .map(|c| corner(k + c[2], j + c[1], i + c[0]))
+                    .collect();
+                fluid += tet_fluid_volume(&pts, &vals);
             }
-        }
+            fluid
+        };
+        let (ax, ay, az) = (dy * dz, dx * dz, dx * dy);
+        vol.par_iter_mut()
+            .zip(wall.par_iter_mut())
+            .enumerate()
+            .for_each(|(idx, (v, w))| {
+                let (k, j, i) = (idx / (ny * nx), (idx / nx) % ny, idx % nx);
+                // The six tets fill the unit cube (volume 1).
+                *v = cell_fluid(k, j, i);
+                // Outward normals of the cell's faces times their fluid area,
+                // summed; the wall closes the fluid part of the cell.
+                let sx = (a_u[g.uface(k, j, i + 1)] - a_u[g.uface(k, j, i)]) * ax;
+                let sy = (a_v[g.vface(k, j + 1, i)] - a_v[g.vface(k, j, i)]) * ay;
+                let sz = (a_w[g.wface(k + 1, j, i)] - a_w[g.wface(k, j, i)]) * az;
+                *w = [-sx, -sy, -sz];
+            });
         Self {
             grid,
             phi,

crates/specialized/rtx-cfd/src/solvers/incompressible/embedded3/poisson/device_cg.rs

@@ -96,8 +96,12 @@ impl DeviceCg {
     /// with a singular one among them.
     pub fn new(problem: &Problem, params: &MultigridParameters) -> Self {
         let rt = runtime();
+        let profile = std::env::var("RTX_E3_MOVING_PROFILE").is_ok();
+        let lap = std::time::Instant::now();
         let fine = Level::<f64>::new(problem.clone());
+        let l_level = lap.elapsed();
         let components = Components::find(problem, &fine.cells);
+        let l_components = lap.elapsed();
         let singular_count = components.singular.iter().filter(|&&s| s).count();
         assert!(
             singular_count == 0 || components.members.len() == 1,
@@ -185,8 +189,12 @@ impl DeviceCg {
     /// from the stale hierarchy get no correction rather than a stale one.
     pub fn refresh(&mut self, problem: &Problem, params: &MultigridParameters) {
         let rt = runtime();
+        let profile = std::env::var("RTX_E3_MOVING_PROFILE").is_ok();
+        let lap = std::time::Instant::now();
         let fine = Level::<f64>::new(problem.clone());
+        let l_level = lap.elapsed();
         let components = Components::find(problem, &fine.cells);
+        let l_components = lap.elapsed();
         let singular_count = components.singular.iter().filter(|&&s| s).count();
         assert!(
             singular_count == 0 || components.members.len() == 1,
@@ -217,6 +225,7 @@ impl DeviceCg {
             }
             link_ptr.push(link_idx.len() as u32);
         }
+        let l_links = lap.elapsed();
         self.n_cells = fine.cells.len();
         self.n_blocks = self.n_cells.div_ceil(256).max(1);
         if self.partial.len() < self.n_blocks {
@@ -241,11 +250,27 @@ impl DeviceCg {
         });
         self.singular = singular_count > 0;
         self.active_host = fine.active.clone();
+        let l_upload = lap.elapsed();
         self.key = OperatorKey::of(problem, params);
+        let l_key = lap.elapsed();
         // The V-cycle's finest level follows the operator (its coarser
         // levels stay): the fine level alone, no hierarchy build.
         let fine_level = super::export::export_fine(problem);
+        let l_export = lap.elapsed();
         self.vcycle.refresh_fine(&fine_level);
+        if profile {
+            let ms = |d: std::time::Duration| d.as_secs_f64() * 1e3;
+            eprintln!(
+                "    refresh laps: level {:.0} ms, components {:.0} ms, links {:.0} ms, uploads {:.0} ms, key {:.0} ms, export_fine {:.0} ms, refresh_fine {:.0} ms",
+                ms(l_level),
+                ms(l_components - l_level),
+                ms(l_links - l_components),
+                ms(l_upload - l_links),
+                ms(l_key - l_upload),
+                ms(l_export - l_key),
+                ms(lap.elapsed() - l_export)
+            );
+        }
     }
 
     pub fn n_cells(&self) -> usize {

crates/specialized/rtx-cfd/src/solvers/incompressible/embedded3/poisson/hierarchy.rs

@@ -41,7 +41,7 @@ impl<T: MgScalar> Level<T> {
     pub(crate) fn new(mut problem: Problem) -> Self {
         let (nx, ny, nz) = (problem.nx, problem.ny, problem.nz);
         let n = nx * ny * nz;
-        let ap: Vec<f64> = (0..n).map(|idx| problem.diagonal(idx)).collect();
+        let ap: Vec<f64> = problem.diagonals();
         let active: Vec<bool> = (0..n)
             .map(|idx| problem.active[idx] && ap[idx] > 0.0)
             .collect();

crates/specialized/rtx-cfd/src/solvers/incompressible/embedded3/poisson/problem.rs

@@ -128,6 +128,36 @@ impl Problem {
         }
     }
 
+    /// Every cell's diagonal in one pass over the links (the per-cell
+    /// [`Self::diagonal`] scans every link: `cells × links` on a merged
+    /// operator — 1.8 s per call at 1.45 M cells, S2-2b). Same sums in
+    /// the same order.
+    #[must_use]
+    pub fn diagonals(&self) -> Vec<f64> {
+        let n = self.nx * self.ny * self.nz;
+        let mut link_sum = vec![0.0; n];
+        for &(a, b, c) in &self.links {
+            link_sum[a] += c;
+            link_sum[b] += c;
+        }
+        (0..n)
+            .map(|idx| {
+                let stencil = self.ae[idx]
+                    + self.aw[idx]
+                    + self.an[idx]
+                    + self.as_[idx]
+                    + self.at[idx]
+                    + self.ab[idx]
+                    + self.extra_diag[idx];
+                if self.links.is_empty() {
+                    stencil
+                } else {
+                    stencil + link_sum[idx]
+                }
+            })
+            .collect()
+    }
+
     /// Pure Neumann: no active cell has a Dirichlet contribution.
     #[must_use]
     pub fn is_singular(&self) -> bool {
@@ -144,6 +174,7 @@ impl Problem {
         let (nx, ny, nz) = (self.nx, self.ny, self.nz);
         let links = self.link_lists();
         let mut sum = 0.0;
+        let diagonals = self.diagonals();
         for k in 0..nz {
             for j in 0..ny {
                 for i in 0..nx {
@@ -151,7 +182,7 @@ impl Problem {
                     if !self.active[idx] {
                         continue;
                     }
-                    let ap = self.diagonal(idx);
+                    let ap = diagonals[idx];
                     if ap <= 0.0 {
                         continue;
                     }

crates/specialized/rtx-cfd/src/solvers/incompressible/embedded3/step/device/cut.rs

@@ -135,41 +135,44 @@ impl DeviceCut {
                 1 => (nx, ny + 1, nz),
                 _ => (nx, ny, nz + 1),
             };
+            // Per face, in parallel (S2-2b): the surface velocity within the
+            // band and the open flag.
+            use rayon::prelude::*;
             let mut ubc = vec![0.0; counts[c]];
             let mut opc = vec![0i32; counts[c]];
-            for k in 0..nk {
-                for j in 0..nj {
-                    for i in 0..ni {
-                        let idx = (k * nj + j) * ni + i;
-                        let x = [
-                            (i as f64 + if c == 0 { 0.0 } else { 0.5 }) * h[0],
-                            (j as f64 + if c == 1 { 0.0 } else { 0.5 }) * h[1],
-                            (k as f64 + if c == 2 { 0.0 } else { 0.5 }) * h[2],
-                        ];
-                        ubc[idx] = match shared {
-                            Some(sh) => sh[c][idx],
-                            None if dists[c][idx].abs() <= band => {
-                                mask.surface_velocity_at(body, x, c, t)
-                            }
-                            None => 0.0,
+            ubc.par_iter_mut()
+                .zip(opc.par_iter_mut())
+                .enumerate()
+                .for_each(|(idx, (ub_out, op_out))| {
+                    let (k, j, i) = (idx / (nj * ni), (idx / ni) % nj, idx % ni);
+                    let x = [
+                        (i as f64 + if c == 0 { 0.0 } else { 0.5 }) * h[0],
+                        (j as f64 + if c == 1 { 0.0 } else { 0.5 }) * h[1],
+                        (k as f64 + if c == 2 { 0.0 } else { 0.5 }) * h[2],
+                    ];
+                    debug_assert!(k < nk);
+                    *ub_out = match shared {
+                        Some(sh) => sh[c][idx],
+                        None if dists[c][idx].abs() <= band => {
+                            mask.surface_velocity_at(body, x, c, t)
+                        }
+                        None => 0.0,
+                    };
+                    *op_out = i32::from(if projection {
+                        match c {
+                            0 => mask.u_open(idx),
+                            1 => mask.v_open(idx),
+                            _ => mask.w_open(idx),
+                        }
+                    } else {
+                        let kind = match c {
+                            0 => mask.u_kind(idx),
+                            1 => mask.v_kind(idx),
+                            _ => mask.w_kind(idx),
                         };
-                        opc[idx] = i32::from(if projection {
-                            match c {
-                                0 => mask.u_open(idx),
-                                1 => mask.v_open(idx),
-                                _ => mask.w_open(idx),
-                            }
-                        } else {
-                            let kind = match c {
-                                0 => mask.u_kind(idx),
-                                1 => mask.v_kind(idx),
-                                _ => mask.w_kind(idx),
-                            };
-                            kind == FaceKind::Fluid
-                        });
-                    }
-                }
-            }
+                        kind == FaceKind::Fluid
+                    });
+                });
             ub[c] = ubc;
             open[c] = opc;
         }
@@ -201,20 +204,25 @@ impl DeviceCut {
         let owner: Vec<u32> = (0..nc)
             .map(|i| mask.master(i).unwrap_or(i) as u32)
             .collect();
-        let mut fold_ptr = Vec::with_capacity(nc + 1);
-        let mut fold_idx = Vec::new();
-        let mut slaves_of: Vec<Vec<u32>> = vec![Vec::new(); nc];
+        // The slaves of every cell as a CSR by counting (no per-cell lists).
+        let mut fold_ptr = vec![0u32; nc + 1];
         let mut merged = 0;
         for i in 0..nc {
             if let Some(m) = mask.master(i) {
-                slaves_of[m].push(i as u32);
+                fold_ptr[m + 1] += 1;
                 merged += 1;
             }
         }
-        fold_ptr.push(0u32);
-        for list in &slaves_of {
-            fold_idx.extend_from_slice(list);
-            fold_ptr.push(fold_idx.len() as u32);
+        for i in 0..nc {
+            fold_ptr[i + 1] += fold_ptr[i];
+        }
+        let mut fold_idx = vec![0u32; merged];
+        let mut cursor: Vec<u32> = fold_ptr[..nc].to_vec();
+        for i in 0..nc {
+            if let Some(m) = mask.master(i) {
+                fold_idx[cursor[m] as usize] = i as u32;
+                cursor[m] += 1;
+            }
         }
         let ub_host = ub;
         let ub_dev = [up_f(&ub_host[0]), up_f(&ub_host[1]), up_f(&ub_host[2])];
@@ -333,11 +341,27 @@ impl DeviceStep {
         let t_rebuild = Instant::now();
         let mut fresh_cells = 0;
         if self.solver.is_moving() {
+            // `RTX_E3_MOVING_PROFILE=1`: the laps of the moving path (S2-2b).
+            let profile = std::env::var("RTX_E3_MOVING_PROFILE").is_ok();
+            let lap = Instant::now();
             let mut field = Field::new(g);
             self.download(&mut field);
+            let l_down = lap.elapsed();
             fresh_cells = self.solver.rebuild_moving_mask(&mut field, dt, t_new);
+            let l_mask = lap.elapsed();
             self.upload(&field);
+            let l_up = lap.elapsed();
             self.cut = DeviceCut::build(&self.solver, g, Phase::Projection, t_new);
+            let l_tables = lap.elapsed();
+            if profile {
+                eprintln!(
+                    "    moving laps: download {:.0} ms, host mask {:.0} ms, upload {:.0} ms, projection tables {:.0} ms",
+                    l_down.as_secs_f64() * 1e3,
+                    (l_mask - l_down).as_secs_f64() * 1e3,
+                    (l_up - l_mask).as_secs_f64() * 1e3,
+                    (l_tables - l_up).as_secs_f64() * 1e3
+                );
+            }
             // The operator: refreshed every step, the hierarchy every
             // `RTX_E3_PRECOND_REFRESH` steps (default 10; 1 = rebuild always).
             let every: usize = std::env::var("RTX_E3_PRECOND_REFRESH")
@@ -350,7 +374,14 @@ impl DeviceStep {
                 self.cg = None;
                 self.steps_since_hierarchy = 0;
             } else if let Some(cg) = self.cg.as_mut() {
+                let lap_op = Instant::now();
                 let problem = self.solver.poisson_operator(g, dt);
+                if profile {
+                    eprintln!(
+                        "    operator laps: poisson_operator {:.0} ms",
+                        lap_op.elapsed().as_secs_f64() * 1e3
+                    );
+                }
                 let params = MultigridParameters {
                     precision: self.solver.params.poisson_precision,
                     smoother: self.solver.params.poisson_smoother,
@@ -380,6 +411,13 @@ impl DeviceStep {
             self.cg_dt = dt;
         }
         let rebuild = t_rebuild.elapsed();
+        if std::env::var("RTX_E3_MOVING_PROFILE").is_ok() {
+            eprintln!(
+                "    moving laps: predictor block {:.0} ms, rebuild block (with the operator refresh) {:.0} ms",
+                t_pred.as_secs_f64() * 1e3,
+                rebuild.as_secs_f64() * 1e3
+            );
+        }
         let anchor = self.solver.anchor_cell(g);
         let mut total = 0;
         let mut final_residual = f64::INFINITY;

crates/specialized/rtx-cfd/src/solvers/incompressible/embedded3/step/mod.rs

@@ -272,6 +272,7 @@ impl Solver {
             }
         }
         .map(|mut m| {
+            let lap_closures = std::time::Instant::now();
             m.scheme = self.params.convection_scheme;
             m.density = self.fluid.density;
             m.wall_order = self.params.wall_order;
@@ -284,6 +285,12 @@ impl Solver {
             if self.params.pressure_centroid {
                 m.compute_gradient_weights();
             }
+            if std::env::var("RTX_E3_MOVING_PROFILE").is_ok() {
+                eprintln!(
+                    "    mask laps: face shifts (within build_mask) {:.0} ms",
+                    lap_closures.elapsed().as_secs_f64() * 1e3
+                );
+            }
             m
         })
         .expect("embedded mask")

crates/specialized/rtx-cfd/src/solvers/incompressible/embedded3/step/moving.rs

@@ -18,7 +18,9 @@ impl Solver {
             return 0;
         };
         let mut fresh_cells = 0;
+        let lap = std::time::Instant::now();
         let mut new_mask = self.build_mask(body, field.grid, t_new, dt);
+        let l_build = lap.elapsed();
         if let Some(old_mask) = &self.mask {
             fresh_cells = refill_fresh_cells(old_mask, &new_mask, field);
             let n_in = self.params.aperture_substeps;
@@ -48,6 +50,7 @@ impl Solver {
                 new_mask.set_step_apertures_with(old_mask, &refs);
             }
         }
+        let l_step = lap.elapsed();
         new_mask.impose_from(
             body,
             &field.u_old,
@@ -77,6 +80,15 @@ impl Solver {
                 })
                 .collect();
         }
+        if std::env::var("RTX_E3_MOVING_PROFILE").is_ok() {
+            let ms = |d: std::time::Duration| d.as_secs_f64() * 1e3;
+            eprintln!(
+                "    mask laps: build_mask {:.0} ms, refill + step apertures + merging {:.0} ms, impose + GCL + volumes {:.0} ms",
+                ms(l_build),
+                ms(l_step - l_build),
+                ms(lap.elapsed() - l_step)
+            );
+        }
         self.mask = Some(new_mask);
         fresh_cells
     }