It would be neat to get a step-by-step list of what he did to compile this version of Ruby, what GC variables he used, etc.
ruby-install ruby 2.1.5 -- CC=clang
ruby-install ruby 2.1.5 -p https://raw.githubusercontent.com/skaes/rvm-patchsets/master/patches/ruby/2.1.5/railsexpress/01-zero-broken-tests.patch -p https://raw.githubusercontent.com/skaes/rvm-patchsets/master/patches/ruby/2.1.5/railsexpress/02-improve-gc-stats.patch -p https://raw.githubusercontent.com/skaes/rvm-patchsets/master/patches/ruby/2.1.5/railsexpress/03-display-more-detailed-stack-trace.patch -p https://raw.githubusercontent.com/skaes/rvm-patchsets/master/patches/ruby/2.1.5/railsexpress/04-show-full-backtrace-on-stack-overflow.patch -p https://raw.githubusercontent.com/skaes/rvm-patchsets/master/patches/ruby/2.1.5/railsexpress/05-funny-falcon-stc-density.patch -p https://raw.githubusercontent.com/skaes/rvm-patchsets/master/patches/ruby/2.1.5/railsexpress/06-funny-falcon-stc-pool-allocation.patch -p https://raw.githubusercontent.com/skaes/rvm-patchsets/master/patches/ruby/2.1.5/railsexpress/07-aman-opt-aset-aref-str.patch -p https://raw.githubusercontent.com/skaes/rvm-patchsets/master/patches/ruby/2.1.5/railsexpress/08-funny-falcon-method-cache.patch -- CC=clang
As for GC, I am not sure it makes much of a difference as it used to back in the days. Probably even less when 2.2 ships with incremental garbage collection. It always depends on the type of work your app does also.