Why does adding concurrency slow down this golang code?

Question

I\'ve got a bit of Go code that I\'ve been tinkering with to answer a little curiosity of mine related to a video game my brother-in-law plays.

Essentially, the cod

Answer 1

Testing your code on my Linux quad core i7 laptop I get this

Here is a Google Spreadsheet

This shows that under Linux at least the scaling is very nearly linear per core.

I think there may be two reasons why you aren't seeing this.

The first is that your macbook air only has 2 real cores. It has 4 hyperthreads though which is why it reports 4 as max cpus. A hyperthread typically only gives an extra 15% performance over a single core rather than the 100% you might expect. So stick to benchmarking 1 or 2 CPUs only on the macbook air!

The other reason might be OS X thread performance compared to Linux. They use different threading models which may be affecting performance.