Two-level scheduling: Difference between revisions

Revision as of 19:19, 8 February 2005

Revision as of 15:47, 8 March 2005

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'''Two-level scheduling''' is a [[Computer science]] term to describe a method to more efficiently perform process [[scheduling]] that involves [[swapped out]] [[process (computing)|processes]].

Consider this problem; A system containcontains 50 running processes all with equal priority. However, the system's [[memory]] can only hold 10 processes in memory simultaneously. Therefore, there will always be 40 processes swapped out written on [[virtual memory]] on the [[hard disk]]. The time taken to swap out and swap in a process is 50 ms respectively.

With straightforward [[Round-robin scheduling]], at every time a [[context switch]] occurs, there would be an 80% probability (40/50, if it chooses randomly among the processes) that a process would need to be swapped in. If that occurs, then obviously a process also need to be swapped out. Swapping in and out of memory is costly, and the scheduler would waste much of its time doing unneeded swaps.