Performance profiling improvements #3

Panos Astithas past at mozilla.com
Mon Oct 22 21:20:32 UTC 2018


Hello folks!

It has been another 3 months since our last update on the Firefox Profiler.
During this time the Performance Tools team and our brilliant contributors
have made many improvements that should make using the tool a more
delightful experience.

Here are the highlights:

# New Categorized Activity Timeline
Perhaps the most prominent change is that the default graph format has
changed. Instead of displaying a bar graph of the sampled stack length, the
tool now shows the type of activity that occurred at a specific point in
time (blue: DOM, purple: layout, green: graphics, yellow: JS, orange:
GC/CC, gray: other, empty: idle). You can switch between the activity graph
and the stack graph using the radio buttons above the thread & process list.

# Navigate faster with the Loupe View
For those used to timelines in movie editing software, there is an
additional timeline view at the top of the call tree panel that combines
the category view with an inverted stack chart view. You can use it to
quickly navigate the selected thread’s timeline: shift+scroll to zoom,
scroll to pan, click to focus the call tree on the selected area.

# Dimmed idle stacks
When selecting the traditional stack graph view, idle stacks are now
dimmed, making it easier to focus on the profile areas that matter.

# Grouped thread & track list
The thread list has also been updated to group the main thread of each
process with the other threads in the same process. Furthermore, there will
be additional tracks for network traffic per process that focus the network
panel on selection, where one can inspect the requests made in that
process. The grouping and the extra tracks are also selectable in the
context menu when right-clicking on the thread list, where you can also
select to display any idle threads that are automatically hidden by
default. Unhiding threads can be useful when one is interested in the 1% of
non-idle activity that occurs in a predominantly idle thread.

# Screenshot capturing (OSX only, more coming!)
On macOS systems with Web Render disabled, the profiler add-on has an
additional setting to capture screenshots of the open windows. This should
help understand to what visual state of the browser the various events
correspond. Support for more platforms will come in the future.

# Filter across all panels
All six bottom panels can now be filtered by specific strings that will
limit the display to the stacks or markers containing said string.

# Import native `perf` traces
Two of the current limitations of the profiler are that it can’t profile
the very early phase of browser startup (before the profiler code has been
initialized) and that it imposes some small overhead when recording. The
overhead increases when one increases the number of sampled threads. One
nice workaround for both problems that still lets you use the profiler UI
to investigate is recording a profile on Linux with the ‘perf’ tool and
then importing the output from https://perf-html.io/. The profiler can
parse the recorded profile and display the aggregated stacks (but of course
without markers). To record a profile with the ‘perf’ command run the
following commands and then load the firefox.symbol.data output file from
https://perf-html.io:
> sudo perf record -g -F 999 -p <firefox-bin-pid>
> sudo perf script -F +pid > firefox.symbol.data

# Remote profiling for Gecko on Android
Finally, profiling Fennec or GeckoView nightlies has been improved, by
removing the overhead imposed by devtools and adding symbols for native
Android libraries. Documentation on remote profiling Android is available
at https://perf-html.io/docs/#/./guide-remote-profiling

We would like to encourage everyone to try these new features out and let
us know of anything that we could improve. If you come across a performance
bug while you are at it, please remember to file a bug and tag it with [qf]
in the whiteboard. Our performance team will be happy to investigate.

Happy profiling!

Panos, on behalf of the perf tools team
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