Optimize BufferLine.copyFrom sparse map copying
Skip O(cols) _copyCellMapsFrom loop when the source line has no sparse combined/extended map entries (scroll recycle from cached blank line). Copy sparse entries by map keys only when needed. Add CDP profiling script and BufferLine.copyFrom micro-benchmark. Co-authored-by: Daniel Imms <Tyriar@users.noreply.github.com>
This commit is contained in:
Cursor Agent
co-authored by
Daniel Imms
Daniel Imms
parent
f3f4dcaf9f
commit
9872be0c29
@@ -0,0 +1,140 @@
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/**
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* Copyright (c) 2026 The xterm.js authors. All rights reserved.
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* @license MIT
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*
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* CPU profile `timeout 1s yes` on the demo terminal via CDP (Chromium).
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*
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* Usage:
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* node bin/profile_yes_cdp.mjs [--out path.cpuprofile] [--label baseline]
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*
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* Requires demo server on port 3000 (npm start).
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*/
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import { chromium } from 'playwright';
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import { writeFileSync, mkdirSync, readFileSync } from 'fs';
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import { dirname, join } from 'path';
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import { fileURLToPath } from 'url';
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const __dirname = dirname(fileURLToPath(import.meta.url));
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const root = join(__dirname, '..');
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function parseArgs() {
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const args = process.argv.slice(2);
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let out = join(root, 'out-test', 'yes.cpuprofile');
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let label = 'profile';
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for (let i = 0; i < args.length; i++) {
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if (args[i] === '--out' && args[i + 1]) {
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out = args[++i];
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label = out.replace(/\.cpuprofile$/, '').split('/').pop() ?? label;
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} else if (args[i] === '--label' && args[i + 1]) {
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label = args[++i];
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}
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}
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return { out, label };
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}
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const INTEREST = [
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'copyFrom',
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'_copySparseMapsFrom',
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'_copyCellMapsFrom',
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'BufferService.scroll'
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];
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export function summarizeCpuProfileFromObject(profile, label = 'profile') {
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const nodes = profile.nodes ?? [];
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const samples = profile.samples ?? [];
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const timeDeltas = profile.timeDeltas ?? [];
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const idToNode = new Map(nodes.map(n => [n.id, n]));
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const stats = new Map(INTEREST.map(n => [n, { hitCount: 0, selfTimeUs: 0, totalTimeUs: 0 }]));
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let totalSampleUs = 0;
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for (let i = 0; i < samples.length; i++) {
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const deltaUs = timeDeltas[i] ?? 0;
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totalSampleUs += deltaUs;
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const stack = [];
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let nodeId = samples[i];
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while (nodeId !== undefined) {
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const node = idToNode.get(nodeId);
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if (!node) break;
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stack.push(node);
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nodeId = node.parent;
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}
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for (const s of INTEREST) {
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if (stack.some(n => (n.callFrame?.functionName ?? '').includes(s))) {
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const st = stats.get(s);
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st.hitCount++;
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st.totalTimeUs += deltaUs;
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}
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}
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const leaf = stack[0];
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const fn = leaf?.callFrame?.functionName ?? '';
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for (const s of INTEREST) {
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if (fn.includes(s)) {
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stats.get(s).selfTimeUs += deltaUs;
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break;
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}
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}
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}
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const rows = [...stats.entries()]
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.filter(([, v]) => v.hitCount > 0)
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.map(([name, v]) => ({
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name,
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hitCount: v.hitCount,
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selfMs: +(v.selfTimeUs / 1000).toFixed(2),
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totalMs: +(v.totalTimeUs / 1000).toFixed(2),
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pctTotal: totalSampleUs ? +((100 * v.totalTimeUs) / totalSampleUs).toFixed(2) : 0
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}));
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return { label, totalSampleMs: +(totalSampleUs / 1000).toFixed(2), rows };
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}
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export function summarizeCpuProfile(profilePath) {
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const profile = JSON.parse(readFileSync(profilePath, 'utf8'));
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return summarizeCpuProfileFromObject(profile, profilePath);
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}
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async function main() {
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const { out, label } = parseArgs();
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mkdirSync(dirname(out), { recursive: true });
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const browser = await chromium.launch({ headless: true });
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const page = await browser.newPage();
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await page.goto('http://localhost:3000/', { waitUntil: 'networkidle' });
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await page.waitForFunction(() => window.term && window.term.element, undefined, { timeout: 60000 });
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const termInfo = await page.evaluate(() => ({
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cols: window.term.cols,
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rows: window.term.rows,
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scrollback: window.term.options.scrollback
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}));
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console.log('Terminal:', JSON.stringify(termInfo));
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const cdp = await page.context().newCDPSession(page);
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await cdp.send('Profiler.enable');
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await cdp.send('Profiler.setSamplingInterval', { interval: 100 });
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await cdp.send('Profiler.start');
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const textarea = page.locator('.xterm-helper-textarea');
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await textarea.click();
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await page.keyboard.type('timeout 1s yes', { delay: 5 });
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await page.keyboard.press('Enter');
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await page.waitForTimeout(2500);
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const { profile } = await cdp.send('Profiler.stop');
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writeFileSync(out, JSON.stringify(profile));
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const summary = summarizeCpuProfileFromObject(profile, label);
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const summaryPath = out.replace(/\.cpuprofile$/, '.summary.json');
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writeFileSync(summaryPath, JSON.stringify({ ...summary, termInfo }, null, 2));
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console.log('Wrote', out);
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console.log('Summary:', JSON.stringify(summary, null, 2));
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await browser.close();
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}
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main().catch(err => {
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console.error(err);
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process.exit(1);
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});
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@@ -23,6 +23,15 @@ const enum Constants {
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CLEANUP_THRESHOLD = 2
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}
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function hasSparseMapEntries(map: object): boolean {
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for (const key in map) {
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if (Object.prototype.hasOwnProperty.call(map, key)) {
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return true;
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}
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}
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return false;
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}
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/**
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* Cell member indices.
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*
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@@ -617,10 +626,24 @@ export class BufferLine implements IBufferLine {
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/** Rebuild sparse maps from another line, keyed only by `_data` flags. */
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private _copySparseMapsFrom(line: BufferLine): void {
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this._combined = {};
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this._extendedAttrs = {};
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for (let i = 0; i < line.length; i++) {
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this._copyCellMapsFrom(line, i, i);
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const srcCombined = line._combined;
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const srcExtended = line._extendedAttrs;
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if (!hasSparseMapEntries(srcCombined) && !hasSparseMapEntries(srcExtended)) {
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this._combined = {};
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this._extendedAttrs = {};
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return;
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}
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const combined: {[index: number]: string} = {};
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for (const key in srcCombined) {
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combined[+key] = srcCombined[+key];
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}
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const extendedAttrs: {[index: number]: IExtendedAttrs | undefined} = {};
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for (const key in srcExtended) {
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extendedAttrs[+key] = srcExtended[+key];
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}
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this._combined = combined;
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this._extendedAttrs = extendedAttrs;
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}
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}
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@@ -0,0 +1,55 @@
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/**
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* Copyright (c) 2026 The xterm.js authors. All rights reserved.
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* @license MIT
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*/
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import { perfContext, before, RuntimeCase } from 'xterm-benchmark';
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import { BufferLine } from 'common/buffer/BufferLine';
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import { BufferLineStringCache } from 'common/buffer/BufferLineStringCache';
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import { DEFAULT_ATTR_DATA } from 'common/buffer/BufferLine';
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import { CellData } from 'common/buffer/CellData';
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import { NULL_CELL_CHAR, NULL_CELL_WIDTH, NULL_CELL_CODE } from 'common/buffer/Constants';
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const ITERATIONS = 500_000;
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const stringCache = new BufferLineStringCache();
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const nullCell = CellData.fromCharData([0, NULL_CELL_CHAR, NULL_CELL_WIDTH, NULL_CELL_CODE]);
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const yCell = CellData.fromCharData([0, 'y', 1, 'y'.charCodeAt(0)]);
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function setupScrollRecyclePair(cols: number): { recycled: BufferLine; blank: BufferLine } {
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const blank = new BufferLine(stringCache, cols, nullCell, false);
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const recycled = new BufferLine(stringCache, cols, yCell, false);
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for (let i = 0; i < cols; i++) {
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recycled.setCellFromCodepoint(i, 'y'.charCodeAt(0), 1, DEFAULT_ATTR_DATA);
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}
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return { recycled, blank };
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}
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perfContext('BufferLine.copyFrom (scroll recycle)', () => {
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perfContext('cols=80', () => {
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let recycled: BufferLine;
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let blank: BufferLine;
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before(() => {
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({ recycled, blank } = setupScrollRecyclePair(80));
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});
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new RuntimeCase('', () => {
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for (let i = 0; i < ITERATIONS; i++) {
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recycled.copyFrom(blank);
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}
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return { payloadSize: ITERATIONS };
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}, { fork: false }).showAverageRuntime();
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});
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perfContext('cols=279', () => {
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let recycled: BufferLine;
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let blank: BufferLine;
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before(() => {
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({ recycled, blank } = setupScrollRecyclePair(279));
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});
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new RuntimeCase('', () => {
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for (let i = 0; i < ITERATIONS; i++) {
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recycled.copyFrom(blank);
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}
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return { payloadSize: ITERATIONS };
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}, { fork: false }).showAverageRuntime();
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});
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});
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