Extended performance test.
With 10 s runtime I get on my laptop:
Type	Events/s  seconds/event cycles/event
Plain  210000000  0.000000005 	14
FW        135330  0.000007389   20700
NoFW       19126  0.000052285   146398

Event means a loop iteration with one empty fwrite().
Where FW indicates with FW and Plain without any instrumentation.