Quick how to explaining how to profile Blink tests on Linux and analyze the results using flame graphs.

Interactive Example

Prerequisites

• perf - available in the package linux-tools on Ubuntu.
• FlameGraph - FlameGraph.zip or see github page.

Instructions

To get profiling data one needs to build chromium and/or content_shell with GYP_DEFINE+="profiling=1"

The basic strategy is to do the following:

1. Build with GYP_DEFINE+="profiling=1"
2. Record using perf record.
3. Collapse stacks using stackcollapse-perf.pl.
4. Generate flame graph using flamegraph.pl.

Profiling a Performance Test

For example, to profile and generate a visualization for the Blink Layout/line-layout.html performance tests the following command sequence could be used. This assumes that the FlameGraph software from above is in the PATH.

  GYP_DEFINES+="profiling=1" gclient runhooks
  ninja -C out/Release blink_tests
  perf record -F 500 -g -q -- ./out/Release/content_shell \
  --dump-render-tree `pwd`/third_party/WebKit/PerformanceTests/Layout/line-layout.html
  perf script | stackcollapse-perf.pl | flamegraph.pl > /tmp/flamegraph.svg

Analyzing the Results

The generated SVG file is an interactive document that can be opened in Chrome (or any other browser). Clicking a stack frame will "zoom in" to that frame. See the Flame Graphs home page for further information and other use cases.

Further Reading

• Chromium profiling on linux.