Bug 1550034 - avoid most failures of the browser_startup_mainthreadio…

….js and browser_startup_content_mainthreadio.js tests. r=mconley a=test-only CLOSED TREE

This patch contains the following changes:
- upload a startup profile when there are unused mainthread I/O whitelist entries,
- avoid 'unused whitelist entry' failures in devedition beta builds (where the IOInterposer is ifdef'ed out) while keeping coverage that ensures we are able to produce valid startup profiles,
- completely disable on Windows Arm64 where the IO interposer is broken,
- mark as ignoreIfUnused the whitelist entry that caused most intermittent failures.

Differential Revision: https://phabricator.services.mozilla.com/D31268

--HG--
extra : source : 742a8ae0110dc3d862a637e4348b587fe431938f

browser/base/content/test/performance/browser_startup_content_mainthreadio.js

@@ -86,6 +86,7 @@ const processes = {
     { // bug 1357205
       path: "XREAppFeat:[email protected]",
       condition: !WIN,
+      ignoreIfUnused: true,
       stat: 1,
     },
   ],
@@ -344,6 +345,20 @@ add_task(async function() {
       }
     }
 
+    if (!whitelist.length) {
+      continue;
+    }
+    // The I/O interposer is disabled if !RELEASE_OR_BETA, so we expect to have
+    // no I/O marker in that case, but it's good to keep the test running to check
+    // that we are still able to produce startup profiles.
+    is(markers.length > 0, !AppConstants.RELEASE_OR_BETA,
+       procName + " startup profiles should have IO markers in builds that are not RELEASE_OR_BETA");
+    if (!markers.length) {
+      // If a profile unexpectedly contains no I/O marker, avoid generating
+      // plenty of confusing "unused whitelist entry" failures.
+      continue;
+    }
+
     for (let entry of whitelist) {
       for (let op in entry) {
         if (["path", "condition", "ignoreIfUnused", "_used"].includes(op)) {
@@ -361,6 +376,7 @@ add_task(async function() {
       }
       if (!("_used" in entry) && !entry.ignoreIfUnused) {
         ok(false, `unused whitelist entry ${procName}: ${entry.path}`);
+        shouldPass = false;
       }
     }
   }
@@ -377,7 +393,7 @@ add_task(async function() {
     await OS.File.writeAtomic(profilePath,
                               encoder.encode(JSON.stringify(startupRecorder.data.profile)));
     ok(false,
-       "Found some unexpected main thread I/O during child process startup; " +
+       "Unexpected main thread I/O behavior during child process startup; " +
        "profile uploaded in " + filename);
   }
 });

browser/base/content/test/performance/browser_startup_mainthreadio.js

@@ -784,6 +784,7 @@ add_task(async function() {
     const dataCol = profile.markers.schema.data;
 
     let markersForCurrentPhase = [];
+    let foundIOMarkers = false;
 
     for (let m of profile.markers.data) {
       let markerName = profile.stringTable[m[nameCol]];
@@ -807,6 +808,18 @@ add_task(async function() {
                                    filename: markerData.filename,
                                    source: markerData.source,
                                    stackId: stack});
+      foundIOMarkers = true;
+    }
+
+    // The I/O interposer is disabled if !RELEASE_OR_BETA, so we expect to have
+    // no I/O marker in that case, but it's good to keep the test running to check
+    // that we are still able to produce startup profiles.
+    is(foundIOMarkers, !AppConstants.RELEASE_OR_BETA,
+       "The IO interposer should be enabled in builds that are not RELEASE_OR_BETA");
+    if (!foundIOMarkers) {
+      // If a profile unexpectedly contains no I/O marker, it's better to return
+      // early to avoid having plenty of confusing "unused whitelist entry" failures.
+      return;
     }
   }
 
@@ -899,6 +912,7 @@ add_task(async function() {
       }
       if (!("_used" in entry) && !entry.ignoreIfUnused) {
         ok(false, `unused whitelist entry ${phase}: ${entry.path}`);
+        shouldPass = false;
       }
     }
   }
@@ -915,7 +929,7 @@ add_task(async function() {
     await OS.File.writeAtomic(profilePath,
                               encoder.encode(JSON.stringify(startupRecorder.data.profile)));
     ok(false,
-       "Found some unexpected main thread I/O during startup; profile uploaded in " +
+       "Unexpected main thread I/O behavior during startup; profile uploaded in " +
        filename);
   }
 });

browser/base/content/test/performance/io/browser.ini

@@ -1,6 +1,8 @@
 [DEFAULT]
 # Currently disabled on debug due to debug-only failures, see bug 1549723.
-skip-if = debug || (os == "linux" && asan) # bug 1549729
+# Disabled on Linux asan due to bug 1549729.
+# Disabled on Windows Arm64 due to bug 1551493.
+skip-if = debug || (os == "linux" && asan) || (os == "win" && processor == "aarch64")
 # to avoid overhead when running the browser normally, startupRecorder.js will
 # do almost nothing unless browser.startup.record is true.
 # gfx.canvas.willReadFrequently.enable is just an optimization, but needs to be