WebGPU RT: GPU timestamp-query per-pass harness
Request the timestamp-query feature; write begin/end timestamps around each wavefront pass via timestampWrites; resolve + read back (deferred to after submit) and print a per-pass us breakdown ~1x/sec. RTStress @ 512 instances, 1920x995: TRACE dominates, total ~1.8-3.0ms/frame. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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1 changed files with 97 additions and 6 deletions
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@ -146,7 +146,10 @@ clamp("maxComputeWorkgroupSizeX", 1024);
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clamp("maxBufferSize", 1 << 30);
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clamp("maxStorageBufferBindingSize", 1 << 30);
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clamp("maxComputeWorkgroupsPerDimension", 65535);
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const device = await adapter.requestDevice({ requiredLimits });
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// Per-pass GPU timing for the wavefront tracer (RTStress HUD / PR numbers).
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const tsSupported = adapter.features && adapter.features.has("timestamp-query");
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const requiredFeatures = tsSupported ? ["timestamp-query"] : [];
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const device = await adapter.requestDevice({ requiredLimits, requiredFeatures });
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const queue = device.queue;
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const ctx = canvas.getContext("webgpu");
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const canvasFormat = "rgba8unorm"; // match storage textures, skip swizzle blit
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@ -935,6 +938,23 @@ env.wgpuFrameEnd = () => {
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queue.submit([state.encoder.finish()]);
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state.encoder = null;
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// Map the wavefront timestamp readback (its resolve/copy was encoded on
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// the just-submitted encoder) and log a per-pass breakdown ~1×/sec.
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if (state.tsReadPending) {
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const ts = state.tsReadPending;
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state.tsReadPending = null;
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const n = ts.pendingLabels.length;
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ts.readBuf.mapAsync(GPUMapMode.READ, 0, 2 * n * 8).then(() => {
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const data = new BigInt64Array(ts.readBuf.getMappedRange(0, 2 * n * 8).slice(0));
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ts.readBuf.unmap();
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ts.inFlight = false;
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wfLogTimestamps(ts, data);
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}).catch((e) => {
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ts.inFlight = false;
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console.error("[crafter-wgpu] timestamp readback failed:", e);
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});
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}
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// Kick off mapAsync for the readbacks whose copyBufferToBuffer we
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// piggy-backed onto the just-submitted encoder. Doing this after
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// submit ensures the map waits for that submission's GPU work to
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@ -2955,6 +2975,51 @@ function ensureWavefrontBuffers(W, H) {
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return wf;
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}
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// ── GPU timestamp-query harness ──────────────────────────────────────────
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//
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// One QuerySet with 2 slots per wavefront pass; each beginComputePass writes
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// begin/end timestamps. After the passes we resolve into a buffer and read
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// it back (deferred to after submit, like the readback path). Deltas are
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// summed per pass label and printed ~1×/sec as a per-pass breakdown.
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const WF_TS_MAX_PASSES = 64; // covers maxDepth up to ~20
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function wfEnsureTimestamps() {
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if (!tsSupported) return null;
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if (rtState.ts) return rtState.ts;
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const cap = 2 * WF_TS_MAX_PASSES;
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rtState.ts = {
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capacity: cap,
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querySet: device.createQuerySet({ type: "timestamp", count: cap }),
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resolveBuf: device.createBuffer({ size: cap * 8,
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usage: GPUBufferUsage.QUERY_RESOLVE | GPUBufferUsage.COPY_SRC }),
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readBuf: device.createBuffer({ size: cap * 8,
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usage: GPUBufferUsage.MAP_READ | GPUBufferUsage.COPY_DST }),
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inFlight: false,
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lastLog: 0,
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pendingLabels: null,
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};
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return rtState.ts;
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}
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function wfLogTimestamps(ts, data) {
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// data: BigInt64Array of ns timestamps, [begin0,end0,begin1,end1,...].
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const now = Date.now();
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if (now - ts.lastLog < 1000) return; // throttle to ~1/sec
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ts.lastLog = now;
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const labels = ts.pendingLabels;
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if (!labels) return;
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const sums = new Map(); // label → ns
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let totalNs = 0;
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for (let i = 0; i < labels.length; i++) {
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const dt = Number(data[2*i + 1] - data[2*i + 0]);
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if (dt < 0) continue;
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sums.set(labels[i], (sums.get(labels[i]) || 0) + dt);
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totalNs += dt;
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}
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const order = ["GENERATE", "PREP", "TRACE", "SHADE", "RESOLVE"];
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const parts = order.filter(k => sums.has(k))
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.map(k => `${k} ${(sums.get(k)/1000).toFixed(1)}us`);
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console.log(`[crafter-wgpu] RT passes: ${parts.join(" | ")} | total ${(totalNs/1000).toFixed(1)}us`);
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}
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env.wgpuLoadRTPipeline = (wgslPtr, wgslLen, bindingsPtr, bindingsCount) => {
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if (!rtState.vertHeap) rtInit();
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const userPart = new TextDecoder().decode(memU8().subarray(wgslPtr, wgslPtr + wgslLen));
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@ -3187,9 +3252,27 @@ env.wgpuDispatchRT = (pipelineHandle, pushPtr, pushBytes,
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const setUser = (pass) => { for (const u of userBgs) pass.setBindGroup(u.group, u.bindGroup); };
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// GPU timing: write begin/end timestamps around each pass (2 query
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// slots per pass), then resolve + read back after submit.
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const ts = wfEnsureTimestamps();
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const capture = !!(ts && !ts.inFlight);
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const tsLabels = [];
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const beginPass = (label, tsName) => {
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const desc = { label };
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if (capture && tsLabels.length < WF_TS_MAX_PASSES) {
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desc.timestampWrites = {
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querySet: ts.querySet,
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beginningOfPassWriteIndex: 2 * tsLabels.length,
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endOfPassWriteIndex: 2 * tsLabels.length + 1,
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};
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tsLabels.push(tsName);
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}
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return enc.beginComputePass(desc);
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};
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// GENERATE
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{
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const p = enc.beginComputePass({ label: "wf-generate" });
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const p = beginPass("wf-generate", "GENERATE");
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p.setPipeline(pipe.genPipe);
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p.setBindGroup(0, paramsBg, [slotOff(0)]);
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p.setBindGroup(1, dataBg);
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@ -3203,7 +3286,7 @@ env.wgpuDispatchRT = (pipelineHandle, pushPtr, pushBytes,
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const shadeSlot = 1 + 3 * d + 2;
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// PREP — publish indirect args, zero next counter.
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{
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const p = enc.beginComputePass({ label: "wf-prep" });
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const p = beginPass("wf-prep", "PREP");
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p.setPipeline(pipe.prepPipe);
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p.setBindGroup(0, paramsBg, [slotOff(prepSlot)]);
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p.setBindGroup(1, dataBg);
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@ -3213,7 +3296,7 @@ env.wgpuDispatchRT = (pipelineHandle, pushPtr, pushBytes,
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}
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// TRACE — indirect over the live ray list.
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{
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const p = enc.beginComputePass({ label: "wf-trace" });
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const p = beginPass("wf-trace", "TRACE");
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p.setPipeline(pipe.tracePipe);
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p.setBindGroup(0, paramsBg, [slotOff(traceSlot)]);
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p.setBindGroup(1, dataBg);
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@ -3222,7 +3305,7 @@ env.wgpuDispatchRT = (pipelineHandle, pushPtr, pushBytes,
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}
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// SHADE — indirect; runs user closesthit/miss, may emit + accumulate.
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{
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const p = enc.beginComputePass({ label: "wf-shade" });
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const p = beginPass("wf-shade", "SHADE");
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p.setPipeline(pipe.shadePipe);
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p.setBindGroup(0, paramsBg, [slotOff(shadeSlot)]);
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p.setBindGroup(1, dataBg);
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@ -3233,7 +3316,7 @@ env.wgpuDispatchRT = (pipelineHandle, pushPtr, pushBytes,
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}
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// RESOLVE — tonemap accum → output image.
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{
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const p = enc.beginComputePass({ label: "wf-resolve" });
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const p = beginPass("wf-resolve", "RESOLVE");
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p.setPipeline(pipe.resolvePipe);
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p.setBindGroup(0, paramsBg, [slotOff(1 + 3 * depth)]);
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p.setBindGroup(1, dataBg);
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@ -3242,6 +3325,14 @@ env.wgpuDispatchRT = (pipelineHandle, pushPtr, pushBytes,
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p.end();
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}
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if (capture && tsLabels.length > 0) {
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enc.resolveQuerySet(ts.querySet, 0, 2 * tsLabels.length, ts.resolveBuf, 0);
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enc.copyBufferToBuffer(ts.resolveBuf, 0, ts.readBuf, 0, 2 * tsLabels.length * 8);
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ts.inFlight = true;
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ts.pendingLabels = tsLabels;
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state.tsReadPending = ts;
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}
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// Reopen the frame's shared pass so wgpuFrameEnd / later UI work as
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// before, and flip ping-pong so the blit picks the texture RESOLVE wrote.
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state.pass = enc.beginComputePass();
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