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Profiling LibSass

Linux perf and pprof

On Linux, you can record the profile with perf and inspect it with pprof.

Install required tools

Pre-requisites:

  1. Linux perf, commonly found in the linux-tools-generic package.
  2. go, for installing pprof.
  3. bazel, for installing perf_to_profile.

First, install pprof with:

go get -u github.com/google/pprof

Then, build and install perf_to_profile:

git clone https://github.com/google/perf_data_converter
cd perf_data_converter
bazel build -c opt src:perf_to_profile
sudo cp bazel-bin/src/perf_to_profile /usr/local/bin/

Finally, in your libsass repository, clone and build sassc:

git clone https://github.com/sass/sassc.git
make sassc

Record perf data

sudo perf record sassc/bin/sassc input.scss > /dev/null && sudo chown $USER:$USER perf.data

This will create a perf.data file that you can vizualize with pprof.

Inspect perf data

A web server with various visualization options:

pprof -http=localhost:3232 sassc/bin/sassc perf.data

Simple text output:

pprof -text sassc/bin/sassc perf.data

Example output:

      flat  flat%   sum%        cum   cum%
  24651348  6.97%  6.97%   24651348  6.97%  [[kernel.kallsyms]]
  20746241  5.87% 12.84%   20746241  5.87%  Sass::SharedPtr::decRefCount
  18401663  5.20% 18.04%   20420896  5.78%  __libc_malloc
  15205959  4.30% 22.34%   15205959  4.30%  [libc-2.27.so]
  12974307  3.67% 26.01%   14070189  3.98%  _int_malloc
  10958857  3.10% 29.11%   10958857  3.10%  Sass::SharedPtr::incRefCount
   9837672  2.78% 31.89%   18433250  5.21%  cfree