If you’re a Flymake user, Mickey over at Mastering Emacs has some advice for you: switch to Flycheck. It’s a drop in replacement for Flymake that has better out-of-the-box language support and is faster. Mickey says that for him the replacement was seamless. “One moment I was using my own duct taped Flymake handlers, and the next I was simply using Flychecks’.”
See Mickey’s post for more details and keybindings. If you like to have your code’s syntax checked on the fly, this is definitely worth a look. And, of course, while you’re there, check out some of Mickey’s other offerings. They’re an extraordinarily good resource.