Lim Jong Seul

The Transactions of the Korea Information Processing Society (1994 ~ 2000), Vol. 1, No. 3, pp. 367-379, Sep. 1994
10.3745/KIPSTE.1994.1.3.367,   PDF Download:

Abstract

This paper describes scheduling algorithms of the UNIX operating system and shows an analytical approach to approximate the average conditional response time for a process in the UNIX operating system. The average conditional response time is the average time between the submittal of a process requiring a certain amount of the CPU time and the completion of the process. The process scheduling algorithms in the UNIX system are based on the priority service disciplines. That is, the behavior of a process is governed by the UNIX process scheduling algorithms that (i) the time-shared computer usage is obtained by allotting each request a quantum until it completes its required CPU time, (ii) the nonpreemptive switching in system mode and the preemptive switching in user mode are applied to determine the quantum, (iii) the first-come-first-serve discipline is applied within the same priority level, and (iv) after completing an allotted quantum the process is placed at the end of either the runnable queue corresponding to its priority of the disk queue where it sleeps. These process scheduling algorithms create the round-robin effect in user mode. Using the round-robin effect and the preemptive switching, we approximate a process delay in user mode. Using the nonpreemptive switching, we approximate a process delay in systems mode. We also consider a process delay due to the disk input and output operations. The average conditional response time is then obtained by approximating the total process delay. The results show an excellent response time for the processes requiring system time at the expense of the processes requiring user time.

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