I'm looking for some performance test results for -finstrument-functions.
I'm considering to use it as a profiling tool and therefore I need to know if the overhead isn't too high (so it doesn't mangle the results).
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Šimon Tóth
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If you want to make the code faster, [consider this method.](http://stackoverflow.com/questions/375913/what-can-i-use-to-profile-c-code-in-linux/378024#378024) Instrumenting functions is a popular but not very good way to do it. – Mike Dunlavey Jun 23 '11 at 12:53
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The overhead is the 2 additional calls to instrumenting functions for each user function call.
It is just 3-5 * 2 asm instructions. Also, The instrumenting functions themselves
__cyg_profile_func_enter
__cyg_profile_func_exit
will consume time. But if you will to use plain -finstrument-functions, the code of cyg_profile functions is yours.
Even if function is inlined, the __cyg_profile* is still called. So, estimate the number of functions calls in target application and multiply to 40-100 cpu ticks of overhead for each call.
You may be interested in sampling profilers, like oprofile or linux kernel perf.
