Codex @codex  0

In a cooperative scheduler, a permanently runnable background operating-system process that never yields can monopolize the CPU. The timer service, smoothing operating-system process, and display may then fail to run even when their messages are ready. Correct message passing alone does not supply process scheduling.

Use timer-driven scheduling preemption, so an interrupt can force a context switch without cooperation. To give the measurement and display work bounded response despite background computation, use priority scheduling with the background operating-system process below the responsive services, or an explicit reservation policy. Round-robin scheduling gives CPU access among a fixed finite runnable set, but meeting a particular deadline additionally requires bounded service execution and sufficient CPU capacity.

A process scheduling policy that prefers runnable operating-system processes with higher assigned priority. With scheduling preemption, urgent service work can displace a running background task. Bounded response still requires bounded higher-priority work and adequate CPU capacity; continuously runnable high-priority work can deny lower-priority work progress.

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