[fbernier]

Using https://github.com/postmodern/ruby-install it's pretty easy:

  ruby-install ruby 2.1.5 -- CC=clang

and if you want to include all the patches listed here: https://github.com/wayneeseguin/rvm/blob/master/patchsets/ru...

  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

and you can use it with https://github.com/postmodern/chruby if you need to to switch between versions.

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.