Profiling
When profiling Servo or troubleshooting performance issues, make sure your build is optimised while still allowing for accurate profiling data.
$ ./mach build --profile profiling --with-frame-pointer
- --profile profiling builds Servo with our profiling configuration
- --with-frame-pointer builds Servo with stack frame pointers on all platforms
Several 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.
TSV Profiling
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.
Generating Timelines
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/
Usage:
-
Use the mouse wheel or trackpad scrolling, with the mouse focused along the top of the timeline, to zoom the viewport in or out.
-
Grab the selected area along the top and drag left or right to side scroll.
-
Hover over a trace to show more information.
Hacking
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.
Sampling profiler
Servo includes a sampling profiler which generates profiles that can be opened in the Gecko profiling tools. To use them:
- Run Servo, loading the page you wish to profile
- Press Ctrl+P (or Cmd+P on macOS) to start the profiler (the console should show "Enabling profiler")
- Press Ctrl+P (or Cmd+P on macOS) to stop the profiler (the console should show "Stopping profiler")
- Keep Servo running until the symbol resolution is complete (the console should show a final "Resolving N/N")
- Run
python etc/profilicate.py samples.json >gecko_samples.jsonto transform the profile into a format that the Gecko profiler understands - Load
gecko_samples.jsoninto https://perf-html.io/
To control the output filename, set the PROFILE_OUTPUT environment variable.
To control the sampling rate (default 10ms), set the SAMPLING_RATE environment variable.
Memory Profiling
Using the -m 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 -m 5 http://example.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.
./mach run --release -m 5 http://example.com/
Begin memory reports 5
|
| 115.15 MiB -- explicit
| 101.15 MiB -- jemalloc-heap-unclassified
| 14.00 MiB -- url(http://example.com/)
| 10.01 MiB -- layout-thread
| 10.00 MiB -- font-context
| 0.00 MiB -- stylist
| 0.00 MiB -- display-list
| 4.00 MiB -- js
| 2.75 MiB -- malloc-heap
| 1.00 MiB -- gc-heap
| 0.56 MiB -- decommitted
| 0.35 MiB -- used
| 0.06 MiB -- unused
| 0.02 MiB -- admin
| 0.25 MiB -- non-heap
| 0.00 MiB -- memory-cache
| 0.00 MiB -- private
| 0.00 MiB -- public
|
| 121.89 MiB -- jemalloc-heap-active
| 111.16 MiB -- jemalloc-heap-allocated
| 203.02 MiB -- jemalloc-heap-mapped
| 272.61 MiB -- resident
|404688.75 MiB -- vsize
|
End memory reports
Using macOS Instruments
Xcode has a instruments tool to profile easily.
First, you need to install Xcode instruments:
$ xcode-select --install
Second, install cargo-instruments via Homebrew:
$ brew install cargo-instruments
Then, you can simply run it via CLI:
$cargo instruments -t Allocations
Here are some links and resources for help with Instruments (Some will stream only on Safari):
- cargo-instruments on crates.io
- Using Time Profiler in Instruments
- Profiling in Depth
- System Trace in Depth
- Threads, virtual memory, and locking
- Core Data Performance Optimization and Debugging
- Learning Instruments
Profiling Webrender
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.