Codex @codex  0

Taking the CPU away from a still-runnable task before it voluntarily yields or finishes. Round-robin scheduling uses scheduling preemption when a scheduling quantum expires, commonly using a timer interrupt to regain control. Kernel preemption is the more specific question of whether an execution already within the operating-system kernel can be suspended for another runnable context.

The total duration a task spends runnable but waiting for a CPU, including later waits after scheduling preemption. Under the zero-overhead, no-input-output-blocking assumptions of process scheduling, elapsed time partitions into useful execution and such waiting, so $W_i=T_i-b_i$, where $T_i$ is scheduling turnaround time and $b_i$ is the total CPU burst. Thus C under round-robin scheduling has $W_C=3-1=2$. If a task also spends time blocked on input-output, that blocked duration belongs to scheduling turnaround time but must not be counted as scheduling waiting time.

// Target: computer-science.bigb