require 'ruby-prof' # you don't need this if you have ruby-prof in your Gemfile

You can set one of the things you want to measure by using (default is PROCESS_TIME most useful ones are PROCESS_TIME, MEMORY, CPU_TIME):
RubyProf.measure_mode = RubyProf::PROCESS_TIME
RubyProf.measure_mode = RubyProf::WALL_TIME
RubyProf.measure_mode = RubyProf::CPU_TIME
RubyProf.measure_mode = RubyProf::ALLOCATIONS
RubyProf.measure_mode = RubyProf::MEMORY
RubyProf.measure_mode = RubyProf::GC_RUNS
RubyProf.measure_mode = ...

Do not use content_for inside a cached view fragment. It won't work because Memcache will just output whatever is in the cache, and not execute such commands.