System Call
The controlled transition through which user-space software requests privileged services from the operating-system kernel.
Operating-System Context
A system call is the controlled interface through which user-space code requests a privileged kernel service. Workloads dominated by many tiny I/O operations can become sensitive to syscall frequency, transitions, copying, and associated scheduling effects.
Cost Boundary
A system call has a different execution path from an ordinary function call, but its cost is not one universal constant. Batching, memory mapping, io_uring, CPU architecture, and kernel implementation can change the measured overhead significantly.