tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index f0c5161e109af3a2c12fd04d7c62fa465c97b961..ca7dee3f7a482ec2b0f47df140d1f9527b37811b 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -3885,12 +3885,66 @@ other types of suffix sets.
   </summary>
 </histogram>
 
-<histogram name="FileBrowser.Load" units="milliseconds">

[Mark P, 2013/08/13 18:28:07]

Please do not delete histograms.  Mark them as obsolete (see example elsewhere
in this file).

[mtomasz, 2013/08/15 03:56:55]

This histogram has never been used. Do we really want to keep it as obsolete? If
so, then why?

[Mark P, 2013/08/15 15:22:51]

Oh, in that case (because it was never emitted to), go ahead and delete it.

+<histogram name="FileBrowser.Load.AdditionalUI" units="milliseconds">
   <summary>
-    Chrome OS File Browser is an built-in extension without a background page.
-    Its main.html file is loaded every time the user opens a File Browser tab or
-    a file chooser dialog. The file is fairly large and the initialization is
-    pretty expensive.
+    Time to load additional UI elements during initialization of Files app. This
+    step loads all other UI elements, which do not require access to the file
+    system.
+  </summary>
+</histogram>
+
+<histogram name="FileBrowser.Load.Display" units="milliseconds">
+  <summary>
+    Time to display the most basic UI of Files.app (without the file list
+    loaded). This includes Load.General, Load.Preference, Load.Strings and
+    Load.EssentialUI. Does not include Load.AdditionalUI nor Load.FileSystem,

[Mark P, 2013/08/13 18:28:07]

Is this exactly (or nearly exactly) the sum of those four histograms, or does
something else take up non-trivial time?

[mtomasz, 2013/08/15 03:56:55]

We shouldn't sum here, since these tasks are called in parallel, and the sum
will be not reliable. For a user it is just time from launching to displaying.

[Mark P, 2013/08/15 15:22:51]

Can you please put some of this explanation in the description?  Instead of
"This includes Load.General, Load.Preference, Load.Strings and
Load.EssentialUI."
it might be better to say for instance something like
"During this time, the tasks measured by the Load.General, Load.Preference,
Load.Strings and Load.EssentialUI histograms are performed.  Some of these
happen in parallel; this histogram is not the sum of those times."

I don't like the passive voice in the first sentence of my suggestion (if you
can rewrite it that would be good), but I think it captures the message.

+    nor Load.FileSystemUI.
+  </summary>
+</histogram>
+
+<histogram name="FileBrowser.Load.EssentialUI" units="milliseconds">
+  <summary>
+    Time to load essential UI elements during initialization of Files app. This
+    step loads only these UI elements required to display the most basic UI.
+    File system is not yet available, nor any other heavy elements.
+  </summary>
+</histogram>
+
+<histogram name="FileBrowser.Load.FileSystem" units="milliseconds">
+  <summary>
+    Time to load the file system during initialization of Files app.
+  </summary>
+</histogram>
+
+<histogram name="FileBrowser.Load.FileSystemUI" units="milliseconds">
+  <summary>
+    Time to load file system related UI elements during initialization of Files
+    app. Only in this UI initialization step, it can be assumed that file system
+    is already available.

[Mark P, 2013/08/13 18:28:07]

Please rephrase last sentence.  Do you mean:
This only measures the UI initialization step, the file system is already
available.
?

[mtomasz, 2013/08/15 03:56:55]

Done.

+  </summary>
+</histogram>
+
+<histogram name="FileBrowser.Load.General" units="milliseconds">

[Mark P, 2013/08/13 18:28:07]

Please come up with a better name.  General makes me think something like total,
but this is not like total at all.  Perhaps CommonData?

[mtomasz, 2013/08/15 03:56:55]

This corresponds the name used in the code. Note, these histograms are for our
internal use, for our performance automated tool.

[Mark P, 2013/08/15 15:22:51]

Okay, that's a plausible reason to keep the name.

+  <summary>
+    Time to load essential data used by other steps of the initialization of
+    Files app.

[Mark P, 2013/08/13 18:28:07]

Please be clear about whether this essential data includes preferences.

Also, does it include strings?

[mtomasz, 2013/08/15 03:56:55]

I am confused. This does not use strings. These are only histograms for our
internal use. Do we need to be so detailed here?

Note, that these histogram names correspond initialization steps in Files app.
See:
https://sites.google.com/a/google.com/chromeos-team-tok/files-app/initialization.
It is complex. I am not sure if we want to explain everything in histogram
descriptions.

[Mark P, 2013/08/15 15:22:51]

Histograms often live long past the date that the original coder moves onto
another project.  Later people, whether newbies to the project or people from
another area of Chrome trying to investigate the scope of a performance problem,
need to have descriptions they can understand.  It's basically the same reason
we comment code well.
 
Thanks for the reference.  I can understand wanting to keep histogram names in
parallel with the names of the functions in the code.

But please rewrite the description to be clear that it doesn't include loading
strings, loading preferences, or any filesystem or ui elements.

+  </summary>
+</histogram>
+
+<histogram name="FileBrowser.Load.Preference" units="milliseconds">
+  <summary>
+    Time to load preferences during initialization of Files app.
+  </summary>
+</histogram>
+
+<histogram name="FileBrowser.Load.Strings" units="milliseconds">
+  <summary>Time to load strings during initialization of Files app.</summary>

[Mark P, 2013/08/13 18:28:07]

Is it useful to separate general data from strings?  I'm having a really hard
time drawing a line that distinguishes one from the other.  If these measure
very different things in the code, perhaps you can give them better names that
make the meaning of the histograms more obvious.

[mtomasz, 2013/08/15 03:56:55]

As before. We want to load strings in parallel to other steps, that's why this
step is separated from other steps. The histogram names correspond the
initialization steps in Files app. Refer to
https://sites.google.com/a/google.com/chromeos-team-tok/files-app/initialization.

[Mark P, 2013/08/15 15:22:51]

Okay.  I think this histogram name and description is fine then if you make the
correction I suggested above regarding the "General" histogram.

+</histogram>
+
+<histogram name="FileBrowser.Load.Total" units="milliseconds">
+  <summary>
+    Total initialization initialization time of Files app. Includes all
+    initialization steps.

[Mark P, 2013/08/13 18:28:07]

Is this basically General + AdditionalUI + FileSystem + FilesystemUI or are
there other things going on too?

[mtomasz, 2013/08/15 03:56:55]

As in the comment. It is said that it includes all initialization steps. But
some of the steps are done in parallel, so the total time is not equal to sum of
them.

To sum up, the initialization process in Files.app is asynchronous, running
steps in dependency order. Therefore the histograms can't be obvious without
understanding the logic, or explaining the entire logic in comments. But, these
histograms are necessary to track performance regressions in each of the
initialization steps, that's why we have them here.

[Mark P, 2013/08/15 15:22:51]

Can you please add something like
"Note that many initialization steps run in parallel."

   </summary>
 </histogram>
 
@@ -3985,6 +4039,13 @@ other types of suffix sets.
   </summary>
 </histogram>
 
+<histogram name="FileBrowser.RootsUpdateTime" units="milliseconds">
+  <summary>
+    Time to enumerate file system roots on initialziation or when a volume is
+    mounted or unmounted.
+  </summary>
+</histogram>
+
 <histogram name="FileBrowser.ViewingFileType" enum="ViewFileType">
   <summary>
     File types that were tried to be viewed through browser. This is recorded
@@ -23036,20 +23097,6 @@ other types of suffix sets.
   <affected-histogram name="Extensions.ExternalExtensionEvent"/>
 </fieldtrial>
 
-<fieldtrial name="FileBrowserLoad" separator=".">
-  <group name="Construct"
-      label="Time spent constructing the main Javascript object."/>
-  <group name="DOM" label="Time to initialize DOM."/>
-  <group name="FileSystem"
-      label="Time to get access to the local file system."/>
-  <group name="Parse" label="Time to parse Javascript and CSS."/>
-  <group name="Roots" label="Time to enumerate file system roots."/>
-  <group name="Total"
-      label="Total load time from the moment the Javascript started parsing
-             till the moment the empty file list is displayed."/>
-  <affected-histogram name="FileBrowser.Load"/>
-</fieldtrial>
-
 <fieldtrial name="HttpPipeliningCompatibility">
   <group name="disable_test" label="Do nothing"/>
   <group name="enable_test" label="Test connection for HTTP pipelining"/>