Rails - Jul 2014 - Huge assets compilation perfomance lag then upgrade to 4.1.4 54720ms vs 879ms

Hello, I try to upgrade existing application from rails 3.2 to rails 4.1

Then I change any 1 line in coffee script server hang for about 1 minute 
and load CPU for 100%

For exemple I make same change for same page for old code

http://pastebin.com/bpMd0KyS - profile log 54720ms vs 879ms

http://pastebin.com/jicn4awq - Gemfile

I comment `gem 'therubyracer', platforms: :ruby` so it use nodejs, when 
rendering takes 9647ms. It's still a lot compare to 879ms in rails 3 and 
therubyracer.

Where can be a problem?

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