Comment by vlovich123

Filesystem stuff tends to be slower than average syscalls because of all the locks and complicated traversals needed. If this is using stat instead of fstat then it’s also going through the VFS layer - repeated calls likely go through the cache fast path for path resolution but accessing the stat structure. There’s also hidden costs in that number like atomic accesses that need to acquire cache line locks that are going to cause hidden contention for other processes on the CPU + the cache dirtying from running kernel code and then subsequently having to repopulate it when leaving all of which adds contended L3/RAM pressure.

In other words, there’s a lot of unmeasured performance degradation that’s a side effect of doing many syscalls above and beyond the CPU time to enter/leave the kernel which itself has shrunk to be negligible. But there’s a reason high performance code is switching to io_uring to avoid that.