perf: load the Git Log scenario's pages with git's latency and scroll across several

perf/budgets.json

@@ -46,7 +46,7 @@
     "consoleOutput.keyMissedFramePct": 10,
     "consoleOutput.tbtMs": 50,
 
-    "gitLog.showMs": 150,
+    "gitLog.showMs": 300,
     "gitLog.droppedFramesPct": 2,
     "gitLog.tbtMs": 50,
     "gitLog.arrowKeyP95Ms": 20,

perf/scenarios.ts

@@ -269,15 +269,18 @@ const scroll: Scenario = {
 
 /**
  * Git Log with 20,000 commits on branching lanes, loaded page by page as the
- * backend does: showing it, walking the selection with the arrow keys (the
- * details pane follows) and wheel-scrolling through it.
+ * backend does (150 ms a page, like `git log`): showing it, walking the
+ * selection with the arrow keys (the details pane follows) and wheel-scrolling
+ * through several pages.
  */
 const gitLog: Scenario = {
   id: "gitLog",
   title: "Show, navigate and scroll a 20k-commit Git Log",
   async run(h) {
     await h.page.evaluate(() =>
-      (window as never as { __openideaPerf: { fakeGitLog(n: number): void } }).__openideaPerf.fakeGitLog(20_000),
+      (
+        window as never as { __openideaPerf: { fakeGitLog(n: number, latencyMs?: number): void } }
+      ).__openideaPerf.fakeGitLog(20_000, 150),
     );
     const showMs = await h.measure(
       () =>
@@ -297,8 +300,9 @@ const gitLog: Scenario = {
     await h.page.mouse.move(box.x + box.width / 2, box.y + box.height / 2);
     const t0 = await h.now();
     await h.inPage((p) => p.startFrames());
-    for (let i = 0; i < 120; i++) {
-      await h.page.mouse.wheel(0, i < 80 ? 400 : -400);
+    // Far enough to load several more pages on the way.
+    for (let i = 0; i < 160; i++) {
+      await h.page.mouse.wheel(0, i < 120 ? 600 : -600);
       await h.page.waitForTimeout(16);
     }
     await h.page.waitForTimeout(200);

src/workbench/perfProbe.ts

@@ -32,9 +32,10 @@ export interface PerfProbe {
   fakeCompletion(items: number): void;
   /**
    * Answers the Git Log with `commits` generated commits (a main line with
-   * feature branches merging into it), paged like the backend. `0` removes it.
+   * feature branches merging into it), paged like the backend, each page after
+   * `latencyMs` (a `git log` call). `0` commits removes it.
    */
-  fakeGitLog(commits: number): void;
+  fakeGitLog(commits: number, latencyMs?: number): void;
 }
 
 const KINDS: CompletionKind[] = [
@@ -159,7 +160,7 @@ export function installPerfProbe(): () => void {
           : null,
       );
     },
-    fakeGitLog(count) {
+    fakeGitLog(count, latencyMs = 0) {
       const commits = Array.from({ length: count }, (_, i) => commit(i, count));
       setRoute(
         "gitLog",
@@ -169,7 +170,8 @@ export function installPerfProbe(): () => void {
               const { skip, limit, range } = (args as { query: LogQuery }).query;
               // Outgoing commits (`@{u}..HEAD`) and the like: none.
               if (range) return Promise.resolve([]);
-              return Promise.resolve(commits.slice(skip, limit ? skip + limit : undefined));
+              const page = commits.slice(skip, limit ? skip + limit : undefined);
+              return new Promise((resolve) => setTimeout(() => resolve(page), latencyMs));
             }
           : null,
       );