New this build: a 'Profile' tab in the debugger, and more debugger improvements!
Profiling means inspecting the performance of some software to identify which parts are the slowest. It displays the CPU time spent running events, broken down to each event sheet and further down in to each event group; the CPU time spent in the physics engine; the CPU time spent on issuing draw calls (i.e. how much time the CPU spent telling the GPU what to do - the GPU still does the actual rendering, but just issuing draw calls can often use a lot of CPU); and the remaining time spent in the Construct 2 engine. Here's what it looks like reporting on Space Blaster:
This helps us quickly see that although the overall CPU usage is low (so there's not a real problem here - remember don't waste your time), at that moment the most CPU consuming events were in the bladeenemy sub-group of the enemies group. So if performance was a problem, that would be a good place to start looking at optimising.
Remember the profiler only shows you what the CPU is doing. Unfortunately it's not possible to retrieve the time spent by the GPU rendering anything, so it's possible the framerate is limited by GPU rendering, which would not show up anywhere in the profiler. The best way to spot that case is if both the framerate and overall CPU are low, you're probably bottlenecked by rendering. On top of that, the 'draw calls' measurement can be misleading in some cases: some browsers will try to complete rendering in that time, making it higher; others will simply forward all the calls to another thread then continue with the rest of the code, meaning it's doing the same amount of work, but the value will measure as a lot less (since it didn't spend much time in the current thread). So remember the measurements may not be exactly accurate.
The profiler is only available with a license. Another reason to upgrade from the free edition!