Engine Profiling
Development < Engine Profiling
Engine Profiling
Linux
Intro
There are several ways to profile an application.
gprof
The compiler injects special code in the binary that self profiles it when it runs. this is what cmake -DCMAKE_BUILD_TYPE=PROFILING is here for. We are not going to use this. It does not interfere with normal program's work-flow. With spring, it gets so slow that it is unusable for profiling anything in late game (which is where it is needed the most). It requires special compiling options.
oprof
OProfile uses statistical sampling. It is a kernel module, which every n clock ticks, registers which function is currently being processed. It is lightweight; it may run with almost 0 performance impact. This method always profiles your profiles your whole system; relevant info has to be filtered out after the profiling run has finished. The downside of statistical profiling, is that it requires at least a certain sample size to achieve good accuracy. Also remember, that oprof still requires the debug symbols, to resolve addresses into function names. It can be turned on/off at any time, so for instance, you may skip spring loading so you would only profile in-game runtime. You can also merge multiple profiling sessions.
Setting up oprof
Required stuff:
- oprof kernel module
- oprof package
Using oprof
You will have to load the kernel module:
sudo insmod oprofile
The profiling daemon is controlled using opcontrol as root. As regular user, you can do post-processing using opreport.
i recommend: call-graph depth of 16 --callgraph=16 separate each thread in it's own profile, you can always merge them using opreport afterwards also, per application profiles too ofc --separate=thread,library
disable kernel profiling, enable userspace profiling --event=CPU_CLK_UNHALTED:100000:0x0f:0:1
there's special statistical sampling timing functions in modern cpu
my laptop's core 2 duo has them
which somehow sets the lower bar generally for recent stuff :p
opcontrol --event=CPU_CLK_UNHALTED:100000:0x0f:0:1 --callgraph=16 --separate-type=thread,library that has to be sent only once & it will ve saved then, to start the profiler: opcontrol --start to stop: opcontrol --stop in order to make the profile data available to userspace, you'll need to dump the data opcontrol --dump
Post processing oprof data
gprof2dot takes oprof data and outputs a nice dot-graph.
Then you can use either graphviz to render to an image, or display the graph directly, for example with xdot.
The will look about like this:
you might need help to output the oprof data in a way that gprof2dot can digest, tell me when you reach there
Windows
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