11th December 2020, 2 min read

ARM MacBook vs Intel MacBook

Up to yesterday, my laptop was a large 15-inch MacBook Pro. It contains an Intel Kaby Lake processor (3.8 GHz). I just got a brand-new 13-inch 2020 MacBook Pro with Apple’s M1 ARM chip (3.2 GHz).

How do they compare? I like precise data points.

Recently, I have been busy benchmarking number parsing routines where you convert a string into a floating-point number. That seems like an interesting comparison. In my basic tests, I generate random floating-point numbers in the unit interval (0,1) and I parse them back exactly. The decimal significand spans 17 digits.

I run the same benchmarking program on both machines. I am compiling both benchmarks identically, using Apple builtin’s Xcode system with the LLVM C++ compiler. Evidently, the binaries will differ since one is an ARM binary and the other is a x64 binary. Both machines have been updated to the most recent compiler and operating system.

My results are as follows:

My benchmarking software is available on GitHub. To reproduce, install Apple’s Xcode (with command line tools), CMake (install for command-line use) and type cmake -B build && cmake --build build && ./build/benchmarks/benchmark. It uses the the default Release mode in CMake (flags -O3 -DNDEBUG).

I do not yet understand why the fast_float library is so much faster on the Apple M1. It contains no ARM-specific optimization.

Note: I dislike benchmarking on laptops. In this case, the tests are short and I do not expect the processors to be thermally constrained.

Update. The original post had the following statement:

In some respect, the Apple M1 chip is far inferior to my older Intel processor. The Intel processor has nifty 256-bit SIMD instructions. The Apple chip has nothing of the sort as part of its main CPU. So I could easily come up with examples that make the M1 look bad.

This turns out to be false. See my post ARM MacBook vs Intel MacBook: a SIMD benchmark