From 590a19baeeeb0fc08a3e75c67829e28afc2d5c83 Mon Sep 17 00:00:00 2001
From: Jack Lukic <jacklukic@gmail.com>
Date: Fri, 5 Jun 2026 12:28:39 -0400
Subject: [PATCH] Bench: Add clean-heap and forced-GC krausest update probes

---
 .../bench/tachometer/bench-krausest.js        | 55 +++++++++++++++++++
 .../tachometer/tachometer-ci-krausest.json    |  8 ++-
 2 files changed, 61 insertions(+), 2 deletions(-)

diff --git a/packages/component/bench/tachometer/bench-krausest.js b/packages/component/bench/tachometer/bench-krausest.js
index 042366dc2..b25f35312 100644
--- a/packages/component/bench/tachometer/bench-krausest.js
+++ b/packages/component/bench/tachometer/bench-krausest.js
@@ -206,6 +206,36 @@ function getRows(el) {
   return el.component.getRows();
 }
 
+/*******************************
+      Update (clean heap)
+      Same workload as update-10th-50 but run first, before the
+      create-heavy ops, so the measured region starts on a clean heap.
+      The delta against update-10th-50 isolates suite-ordering GC cost.
+*******************************/
+
+// Warm render / reconcile / update so the first-op cold JIT doesn't
+// skew the isolated measure.
+const elWarm = await mount();
+elWarm.component.run(1000);
+await flush();
+for (let i = 0; i < 10; i++) {
+  elWarm.component.update();
+  flushWork();
+}
+destroy();
+
+const elIso = await mount();
+elIso.component.run(1000);
+await flush();
+// purpose: Same update workload as update-10th-50 but on a clean heap with no create-heavy ops before it. Pairs with update-10th-50 to isolate suite-ordering GC pressure.
+performance.mark(startMark('update-isolated-50'));
+for (let i = 0; i < 50; i++) {
+  elIso.component.update();
+  flushWork();
+}
+performance.measure('update-isolated-50', startMark('update-isolated-50'));
+destroy();
+
 /*******************************
       Create
       (krausest 01_run, 02b_runlots)
@@ -279,6 +309,31 @@ for (let i = 0; i < 50; i++) {
 performance.measure('update-10th-50', startMark('update-10th-50'));
 destroy();
 
+/*******************************
+      Update (forced GC)
+      update-10th workload with a full GC before the measured region.
+      If the update-10th-50 delta vanishes here, the carried-in cost is
+      reclaimable GC pressure from the create-heavy ops above.
+*******************************/
+
+const el5b = await mount();
+el5b.component.run(1000);
+await flush();
+// gc() exists only under --js-flags=--expose-gc (set in tachometer-ci-krausest.json).
+// Settle after collecting so the measured region starts on a post-GC heap.
+if (globalThis.gc) {
+  globalThis.gc();
+  await flush();
+}
+// purpose: update-10th workload with a forced GC before the measured region. If the update-10th-50 regression vanishes here it is reclaimable GC pressure.
+performance.mark(startMark('update-gc-50'));
+for (let i = 0; i < 50; i++) {
+  el5b.component.update();
+  flushWork();
+}
+performance.measure('update-gc-50', startMark('update-gc-50'));
+destroy();
+
 /*******************************
       Select
       (krausest 05_select)
diff --git a/packages/component/bench/tachometer/tachometer-ci-krausest.json b/packages/component/bench/tachometer/tachometer-ci-krausest.json
index 1831aa38e..98cef950d 100644
--- a/packages/component/bench/tachometer/tachometer-ci-krausest.json
+++ b/packages/component/bench/tachometer/tachometer-ci-krausest.json
@@ -8,13 +8,15 @@
     {
       "name": "this-change",
       "url": "ci-current-krausest.html",
-      "browser": { "name": "chrome", "headless": true },
+      "browser": { "name": "chrome", "headless": true, "addArguments": ["--js-flags=--expose-gc"] },
       "measurement": [
         { "mode": "performance", "entryName": "create-1k" },
         { "mode": "performance", "entryName": "create-10k" },
         { "mode": "performance", "entryName": "replace-1k" },
         { "mode": "performance", "entryName": "append-1k" },
         { "mode": "performance", "entryName": "update-10th-50" },
+        { "mode": "performance", "entryName": "update-isolated-50" },
+        { "mode": "performance", "entryName": "update-gc-50" },
         { "mode": "performance", "entryName": "select-40" },
         { "mode": "performance", "entryName": "swap-rows-20" },
         { "mode": "performance", "entryName": "remove-row-front-20" },
@@ -26,13 +28,15 @@
     {
       "name": "tip-of-tree",
       "url": "ci-baseline-krausest.html",
-      "browser": { "name": "chrome", "headless": true },
+      "browser": { "name": "chrome", "headless": true, "addArguments": ["--js-flags=--expose-gc"] },
       "measurement": [
         { "mode": "performance", "entryName": "create-1k" },
         { "mode": "performance", "entryName": "create-10k" },
         { "mode": "performance", "entryName": "replace-1k" },
         { "mode": "performance", "entryName": "append-1k" },
         { "mode": "performance", "entryName": "update-10th-50" },
+        { "mode": "performance", "entryName": "update-isolated-50" },
+        { "mode": "performance", "entryName": "update-gc-50" },
         { "mode": "performance", "entryName": "select-40" },
         { "mode": "performance", "entryName": "swap-rows-20" },
         { "mode": "performance", "entryName": "remove-row-front-20" },