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Profiling Blink using Flame Graphs

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

Example flame graph.
Interactive Example

Prerequisites

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

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