More system calls mean more overall OS overhead eg. more context switches, or as you say more contention on internal locks etc.
Also, more fs-related system calls mean less available kernel threads to process these system calls. eg. XFS can paralellize mutations only up to its number of allocation groups (agcount)
Also, more fs-related system calls mean less available kernel threads to process these system calls. eg. XFS can paralellize mutations only up to its number of allocation groups (agcount)