Profiling
First, ensure that you are building Servo in release (optimized) mode:
./mach build --release
Three ways to get profiling information about Servo's runs:
##Interval Profiling
Using the -p option followed by a number (time period in seconds), you can spit out profiling information to the terminal periodically. To do so, run Servo on the desired site (URLs and local file paths are both supported) with profiling enabled:
./mach run --release -p 5 https://www.cnn.com/
In the example above, while Servo is still running (AND is processing new passes), the profiling information is printed to the terminal every 5 seconds.
Once the page has loaded, hit ESC (or close the app) to exit. Profiling output will be provided, broken down by area of the browser and URL. For example, if you would like to profile loading Hacker News, you might get output of the form below:
[larsberg@lbergstrom servo]$ ./mach run --release -p 5 http://news.ycombinator.com/
_category_ _incremental?_ _iframe?_ _url_ _mean (ms)_ _median (ms)_ _min (ms)_ _max (ms)_ _events_
Compositing N/A N/A N/A 0.0440 0.0440 0.0440 0.0440 1
Layout no no https://news.ycombinator.com/ 29.8497 29.8497 29.8497 29.8497 1
Layout yes no https://news.ycombinator.com/ 11.0412 10.9748 10.8149 11.3338 3
+ Style Recalc no no https://news.ycombinator.com/ 22.8149 22.8149 22.8149 22.8149 1
+ Style Recalc yes no https://news.ycombinator.com/ 5.3933 5.2915 5.2727 5.6157 3
+ Restyle Damage Propagation no no https://news.ycombinator.com/ 0.0135 0.0135 0.0135 0.0135 1
+ Restyle Damage Propagation yes no https://news.ycombinator.com/ 0.0146 0.0149 0.0115 0.0175 3
+ Primary Layout Pass no no https://news.ycombinator.com/ 3.3569 3.3569 3.3569 3.3569 1
+ Primary Layout Pass yes no https://news.ycombinator.com/ 2.8727 2.8472 2.8279 2.9428 3
| + Parallel Warmup no no https://news.ycombinator.com/ 0.0002 0.0002 0.0002 0.0002 2
| + Parallel Warmup yes no https://news.ycombinator.com/ 0.0002 0.0002 0.0001 0.0002 6
+ Display List Construction no no https://news.ycombinator.com/ 3.4058 3.4058 3.4058 3.4058 1
+ Display List Construction yes no https://news.ycombinator.com/ 2.6722 2.6523 2.6374 2.7268 3
In this example, when loading the page we performed one full layout and three incremental layout passes, for a total of (29.8497 + 11.0412 * 3) = 62.9733ms.
Using the -p option followed by a file name, you can spit out profiling information of Servo's execution to a TSV (tab-separated because certain url contained commas) file. The information is written to the file only upon Servo's termination. This works well with the -x OR -o option so that performance information can be collected during automated runs. Example usage:
./mach run -r -o out.png -p out.tsv https://www.google.com/
The formats of the profiling information in the Interval and TSV Profiling options are the essentially the same; the url names are not truncated in the TSV Profiling option.
Add the --profiler-trace-path=/timeline/output/path.html flag to output the profiling data as a self contained HTML timeline. Because it is a self contained file (all CSS and JS is inline), it is easy to share, upload, or link to from bug reports.
$ ./mach run --release -p 5 --profiler-trace-path=trace.html https://reddit.com/
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Use the mouse wheel or trackpad scrolling, with the mouse focused along the top of the timeline, to zoom the viewport in or out.
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Grab the selected area along the top and drag left or right to side scroll.
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Hover over a trace to show more information.
The JS, CSS, and HTML for the timeline comes from fitzgen/servo-trace-dump and there is a script in that repo for updating servo's copy.
All other code is in the components/profile/ directory.
This option is using the Instruments app on Mac OSX. First, before compiling the release mode, turn on the debug symbols in the Cargo.toml file under the components/servo/ directory by uncommenting the commented lines under [profile.release].
Here are some videos for help with Instruments (they will stream only on Safari):
- Using Time Profiler in Instruments
- Profiling in Depth
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System Trace in Depth
- Threads, virtual memory, and locking
- Core Data Performance Optimization and Debugging
- Learning Instruments
There are no direct performance counters for the layout code in Gecko. Instead, use a sampling profiler (e.g., Instruments.app on OSX or perf on Linux) and sum the time spent in the Reflow* methods.
There are no direct performance counters for the layout code in Chrome. Instead, use a sampling profiler (e.g., Instruments.app on OSX or perf on Linux) and sum the time spent in the layout* methods.
Use the following command to get some profile data from WebRender:
$ ./mach run -w -Z wr-stats --release http://www.nytimes.com
When you run Servo with this command, you'll be looking at three things:
CPU (backend): The amount of time WebRender is packing and batching data. CPU (Compositor): Amount of time WebRender is issuing GL calls and interacting with the driver. GPU: Amount of time the GPU is taking to execute the shaders.