Use only the steady gesture in frame rate tests.

chrome/test/data/perf/frame_rate/head.js

Index: chrome/test/data/perf/frame_rate/head.js
diff --git a/chrome/test/data/perf/frame_rate/head.js b/chrome/test/data/perf/frame_rate/head.js
index 18f8485e27c6e9c3c2df24391d6d507b16b68a54..d92ee93db0b159135a82e64601241b12dd892dc5 100644
--- a/chrome/test/data/perf/frame_rate/head.js
+++ b/chrome/test/data/perf/frame_rate/head.js
@@ -41,12 +41,10 @@ var __old_title = "";
 var __raf_is_live = false;
 var __raf;
 
+var __t_start;
 var __t_last;
 var __t_est;
-var __t_est_total;
-var __t_est_squared_total;
-var __t_count;
-var __t_start;
+var __t_deltas;
 
 var __queued_gesture_functions;
 var __results;
@@ -67,6 +65,10 @@ var __gesture_library = {
     {"time_ms":1, "y":0},
     {"time_ms":5000, "y":0}
   ],
+  steady: [
+    {"time_ms":1, "y":0},
+    {"time_ms":500, "y":400}
+  ],
   reading: [
     {"time_ms":1, "y":0},
     {"time_ms":842, "y":40},
@@ -180,22 +182,31 @@ function __gesture_stretch(gesture, stretch_factor) {
 // Gesture set to use for testing, initialized with default gesture set.
 // Redefine in test file to use a different set of gestures.
 var __gestures = {
-  none: __gesture_library["stationary"],
-  steady: __gesture_library["init"],
-  reading: __gesture_library["reading"],
-  mouse_wheel: __gesture_library["mouse_wheel"],
-  mac_fling: __gesture_library["mac_fling"],
+  steady: __gesture_library["steady"],
 };
 
 function __init_stats() {
   __t_last = undefined;
   __t_est = undefined;
-  __t_est_total = 0;
-  __t_est_squared_total = 0;
-  __t_count = 0;
+  __t_deltas = [];
 }
 __init_stats();
 
+var __cur_chrome_interval;
+function __init_time() {
+  if (chrome.Interval) {
+    __cur_chrome_interval = new chrome.Interval();
+    __cur_chrome_interval.start();
+  }
+}
+__init_time();
+
+function __get_time() {
+  if (__cur_chrome_interval)
+    return __cur_chrome_interval.microseconds() / 1000;
+  return new Date().getTime();
+}
+
 function __init_raf() {
   if ("requestAnimationFrame" in window)
     __raf = requestAnimationFrame;
@@ -211,30 +222,44 @@ function __init_raf() {
     // No raf implementation available, fake it with 16ms timeouts
     __raf = function(callback, element) {
       setTimeout(callback, 16);
-    }
+    };
 }
 __init_raf();
 
 function __calc_results() {
-  var M = __t_est_total / __t_count;
-  var X = __t_est_squared_total / __t_count;
-  var V = X - M * M;
-  var S = Math.sqrt(V);
+  var M = 0.0;
+  var N = __t_deltas.length;
+
+  for (var i = 0; i < N; i++)
+    M += __t_deltas[i];
+  M = M / N;
+
+  var V = 0.0;
+  for (var i = 0; i < N; i++) {
+    var v = __t_deltas[i] - M;
+    V += v * v;
+  }
+
+  var S = Math.sqrt(V / (N - 1));

[jbates, 2011/11/11 23:43:46]

(N - 1) should be N?

[Justin Novosad, 2011/11/14 16:08:42]

Actually N-1 is correct for calculating unbiased sample variance. The unbiased
estimator is always preferable when N is variable.

 
+  // Report frame rate in terms of frames-per-second. However,
+  // report error as an interval. Reporting it as 1/sigma amplifies
+  // the noise and makes it seem higher than it actually is.
+  // TODO(nduca): switch to a smarter measure of noise, possibly something
+  // based on histogram-spikes or percentiles.

[Justin Novosad, 2011/11/14 16:08:42]

I think the right way to do it would be to compute the variance in terms of fps.
To get sigma in fps, you would need to change line 239 to:
var v = 1000.0/__t_deltas[i] - 1000.0/M;
This the result of this is _not_ equivalent to 1/interval_sigma

   var R = new Object();
   R.mean = 1000.0 / M;
-  R.sigma = R.mean - 1000.0 / (M + S);
+  R.sigma = S;
   return R;
 }
 
 function __calc_results_total() {
   if (!__results) {
-    return;
+    return {};
   }
   var size = __results.gestures.length;
   var mean = 0;
   var variance = 0;
-  var sigma;
 
   // Remove any intial caching test(s).
   while (__results.means.length != size) {
@@ -247,7 +272,7 @@ function __calc_results_total() {
   }
   mean /= size;
   variance /= size;
-  sigma = Math.sqrt(variance);
+  var sigma = Math.sqrt(variance);
 
   var results = new Object();
   // GTest expects a comma-separated string for lists.
@@ -260,7 +285,7 @@ function __calc_results_total() {
 }
 
 function __update_fps() {
-  var t_now = new Date().getTime();
+  var t_now = __get_time();
   if (window.__t_last) {
     var t_delta = t_now - __t_last;
     if (window.__t_est) {
@@ -268,12 +293,11 @@ function __update_fps() {
     } else {
       __t_est = t_delta;
     }
+
+    __t_deltas.push(t_delta);
+
     var fps = 1000.0 / __t_est;
     document.title = "FPS: " + (fps | 0);
-
-    __t_est_total += t_delta;
-    __t_est_squared_total += t_delta * t_delta;
-    __t_count++;
   }
   __t_last = t_now;
 }
@@ -283,7 +307,7 @@ function __advance_gesture_recording() {
   var y = document.body.scrollTop;
   // Only add a gesture if the scroll position changes.
   if (__recording.length == 0 || y != __recording[__recording.length - 1].y) {
-    var time_ms = new Date().getTime() - __t_start;
+    var time_ms = __get_time() - __t_start;
     __recording.push({ time_ms: time_ms, y: y });
     return true;
   }
@@ -319,7 +343,7 @@ function __create_gesture_function(gestures) {
       __stop();
       return false;
     }
-    var time_cur = new Date().getTime() - __t_start;
+    var time_cur = __get_time() - __t_start;
     if (time_cur <= gestures[i0].time_ms)
       return false;
 
@@ -385,7 +409,7 @@ function __sched_update() {
       if (__advance_gesture())
         __update_fps();
       else
-        __t_last = new Date().getTime();
+        __t_last = __get_time();
     }
   }, document.body);
 }
@@ -419,7 +443,7 @@ function __start(gesture_function) {
 
   __old_title = document.title;
   __advance_gesture = gesture_function;
-  __t_start = new Date().getTime();
+  __t_start = __get_time();
   __running = true;
   if (!__raf_is_live && !__animation) {
     __sched_update();