When weird performance things like this happens, it can be helpful to test in other environments. If the performance change does not happen in other operating s

When weird performance things like this happens, it can be helpful to test in other environments. If the performance change does not happen in other operating systems or hardware then it suggests that the weird performance you are observing could be due to an unusual coincidence in your particular system. That said, if you do want to figure out why deleting that global variable made a difference then using Linux's perf tool might give you more informationto work with. One time I had a weird program where inserting a NOP instruction in a certain location made it run twice as fast. After investigation we found out that the difference was with branch prediction. The presence or absence of that NOP instruction affected the addresses of the jump targets the inner loop's switch statement. For some reason, the version without the NOP instruction those addresses resulted in lots of branch mispredictions. Perhaps because of a collision in the branch predictor's hash tables.