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'''Two-level scheduling''' is a [[computer science]] term to describe a method to more efficiently perform process [[Scheduling (computing)|scheduling]] that involves [[swapped out]] [[process (computing)|processes]].
Consider this problem: A system contains 50 running processes all with equal priority. However, the system's [[computer storage|memory]] can only hold 10 processes in memory simultaneously. Therefore, there will always be 40 processes swapped out written on [[virtual memory]] on the
With straightforward [[Round-robin scheduling]], every time a [[context switch]] occurs, a process would need to be swapped in (because only the 10 least recently used processes are swapped in). Choosing randomly among the processes would diminish the probability to 80% (40/50). If that occurs, then obviously a process also need to be swapped out. Swapping in and out of is costly, and the scheduler would waste much of its time doing unneeded swaps.
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* [[Andrew S. Tanenbaum|Tanenbaum]], [[Albert Woodhull]], ''Operating Systems: Design and Implementation'', p.92
{{Processor scheduling}}
[[Category:Scheduling algorithms]]▼
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