Let me preface this question by saying that I know it takes programs longer to run in valgrind as there is a lot of overhead. This question is not about that.
To ensure that our implementations of data structures have the appropriate runtime, all test cases time out after a certain amount of time (usually around 10 times the amount of time the teacher produced solutions take to run in Valgrind). I ran the test cases on my laptop early in the day and everything was fine. I made two very minor changes later at night (adding one to something and adding a counter for something else, both of which are constant time operations). I reran the tests and I timed out on even the most basic of test cases, like inserting one node. I was freaking out, so I went to the 24/7 computer lab on campus and ran my code on a virtual machine and it worked fine. I ran the binaries on my laptop and they're speedy. I tried turning my computer off and then back on and that didn't fix anything, so I tried updating valgrind but it is up to date. I removed valgrind and then re-installed and that didn't fix the problem either. To verify it is a problem with valgrind and not my code I made a hello_world.cpp then and ran the binary in valgrind with no extra flags. It takes about 15-20 seconds to run. I have absolutely no idea why this is happening. I've not made any changes to my computer. I've skimmed the valgrind documentation, but I cannot pin down what is wrong. I run Fedora 27.