ruby-prof

ruby-prof is a fast code profiler for Ruby. Its features include:

• Speed - it is a C extension and therefore many times faster than the standard Ruby profiler.
  
• Modes - Ruby prof can measure a number of different parameters, including call times, memory usage and object allocations.
  
• Reports - can generate text and cross-referenced html reports
  
  • Flat Profiles - similar to the reports generated by the standard Ruby profiler
    
  • Graph profiles - similar to GProf, these show how long a method runs, which methods call it and which methods it calls.
    
  • Call tree profiles - outputs results in the calltree format suitable for the KCacheGrind profiling tool.
    
• Threads - supports profiling multiple threads simultaneously
  

https://github.com/wycats/ruby-prof
http://rubylearning.com/blog/2011/08/14/performance-testing-rails-applications-how-to/
http://ruby-prof.rubyforge.org/