Easy steps for CPU profiling a Rails app
- add ruby-prof to your gemfile (https://github.com/ruby-prof/ruby-prof)
- grab kcachegrind or qcachegrind (brew install qcachegrind graphviz on os x)
- plop development_profiler.rb in lib in your app
- wrap your questionable code in a prof block
- open the file in qcachegrind (It'll live in tmp/performance in your app)
I'd give opening the files it generates that way a shot in qcachegrind - I haven't written much Ruby in the past ~4 years, so I wouldn't be shocked if RubyProf's API changed in the intervening time