dart-sass/perf.md

These benchmarks are informal and only intended to give us a general sense of the benefit Dart Sass could provide relative to other implementations.

This was tested against:

• libsass 0f3d6ad1 and sassc 4674821 compiled with g++ (Debian 7.3.0-18) 7.3.0.
• Dart Sass 50a45a7 on Dart 2.4.0 and Node v12.0.0.
• Ruby Sass 8d1edc76 on ruby 2.5.3p105 (2018-10-18 revision 65156) [x86_64-linux].

on Debian x64 with Intel Xeon E5-1650 v3 @ 3.50GHz. The Dart Sass application snapshot was trained on the tool/app-snapshot-input.scss file.

Measurements

I ran five instances of each configuration and recorded the fastest time.

Small Plain CSS

Running on a file containing 4 instances of .foo {a: b}:

• sassc: 0.005s
• Dart Sass from a script snapshot: 0.216s
• Dart Sass native executable: 0.018s
• Dart Sass on Node.js: 0.209s
• Ruby Sass with a hot cache: 0.148s

Based on these numbers, Dart Sass from a native executable is approximately:

• 3.6x slower than libsass
• 11.6x faster than Dart Sass on Node
• 8.2x faster than Ruby Sass

Large Plain CSS

Running on a file containing 2^17 instances of .foo {a: b}:

• sassc: 1.705s
• Dart Sass from a script snapshot: 1.550s
• Dart Sass native executable: 1.518s
• Dart Sass on Node.js: 2.765s
• Ruby Sass with a hot cache: 10.965s

Based on these numbers, Dart Sass from a native executable is approximately:

• 1.1x faster than libsass
• 1.8x faster than Dart Sass on Node
• 7.2x faster than Ruby Sass

Preceding Sparse @extend

Running on a file containing .x {@extend .y}, 2^17 instances of .foo {a: b}, and then .y {a: b}:

• sassc: 1.712s
• Dart Sass from a script snapshot: 1.613s
• Dart Sass native executable: 1.582s
• Dart Sass on Node.js: 2.739s
• Ruby Sass with a hot cache: 16.472s

Based on these numbers, Dart Sass from a native executable is approximately:

• 1.1x faster than libsass
• 1.7x faster than Dart Sass on Node
• 10.4x faster than Ruby Sass

Following Sparse @extend

Running on a file containing .y {a: b}, 2^17 instances of .foo {a: b}, and then .x {@extend .y}:

• sassc: 1.701s
• Dart Sass from a script snapshot: 1.568s
• Dart Sass native executable: 1.543s
• Dart Sass on Node.js: 2.821s
• Ruby Sass with a hot cache: 16.469s

Based on these numbers, Dart Sass from a native executable is approximately:

• 1.1x faster than libsass
• 1.8x faster than Dart Sass on Node
• 10.7x faster than Ruby Sass

Preceding Dense @extend

Running on a file containing .bar {@extend .foo} followed by 2^17 instances of .foo {a: b}:

• sassc: 2.260s
• Dart Sass from a script snapshot: 2.405s
• Dart Sass native executable: 2.526s
• Dart Sass on Node.js: 5.612s
• Ruby Sass with a hot cache: 28.690s

Based on these numbers, Dart Sass from a native executable is approximately:

• 1.1x slower than libsass
• 2.2x faster than Dart Sass on Node
• 11.4x faster than Ruby Sass

Following Dense @extend

Running on a file containing 2^17 instances of .foo {a: b} followed by .bar {@extend .foo}:

• sassc: 2.289s
• Dart Sass from a script snapshot: 2.396s
• Dart Sass native executable: 2.457s
• Dart Sass on Node.js: 6.319s
• Ruby Sass with a hot cache: 28.708s

Based on these numbers, Dart Sass from a native executable is approximately:

• 1.1x slower than libsass
• 2.6x faster than Dart Sass on Node
• 11.7x faster than Ruby Sass

Bootstrap

Running on a file containing 16 instances of importing the Bootstrap framework:

• sassc: 0.767s
• Dart Sass from a script snapshot: 1.534s
• Dart Sass native executable: 0.955s
• Dart Sass on Node.js: 3.156s
• Ruby Sass with a hot cache: 12.521s

Based on these numbers, Dart Sass from a native executable is approximately:

• 1.2x slower than libsass
• 3.3x faster than Dart Sass on Node
• 13.1x faster than Ruby Sass

a11ycolor

Running on a file containing test cases for a computation-intensive color-processing library:

• sassc: 0.248s
• Dart Sass from a script snapshot: 0.736s
• Dart Sass native executable: 0.565s
• Dart Sass on Node.js: 1.043s
• Ruby Sass with a hot cache: 5.091s

Based on these numbers, Dart Sass from a native executable is approximately:

• 2.3x slower than libsass
• 1.8x faster than Dart Sass on Node
• 9.0x faster than Ruby Sass

Susy

Running on a file containing test cases for the computation-intensive Susy grid framework:

• sassc: 0.248s
• Dart Sass from a script snapshot: 0.673s
• Dart Sass native executable: 0.237s
• Dart Sass on Node.js: 0.990s
• Ruby Sass with a hot cache: 1.527s

Based on these numbers, Dart Sass from a native executable is approximately:

• identical to libsass
• 4.2x faster than Dart Sass on Node
• 6.4x faster than Ruby Sass

Prior Measurements

• 1.22.4.
• 1.20.2.
• 1.13.4.
• 1.6.0.
• 1.0.0-alpha.8.
• Pre-alpha, 30 September 2016.
• Pre-alpha, 19 August 2016.
• Pre-alpha, 15 July 2016.

Conclusions

This is the first measurement with Dart Sass running as ahead-of-time-compiled native code, and the results are encouraging. It's well below the 100ms threshold for tiny files, and it's on par with SassC for most test cases. SassC still leads for tests with many extends, although only slightly, and for one of our real-world test cases (although Dart Sass leads in others). The two implementations can be fairly described as having about the same performance overall.

Dart Sass on Node is still substantially slower than on the Dart VM, and that relative slowdown becomes more pronounced as the raw Dart code becomes faster. Solutions for this such as [the embedded protocol][] or [WebAssembly support][] are becoming more and more important.