It has worked fine before I upgrade wp 3.9.2. Since I upgraded, P3 works once and then it is stuck that status. Although I activate or deactivate plugins, it shows exactly same result.
Second problem is the result is not accurate. When I checked the time with timer, my website loading time was around 6 sec. But P3 said 12 sec. Therefore, I am not sure whether it works properly or not recently. But it was helpful when it worked.