An Operating Systems Vade Mecum

44 Time Management Chapter 23C81B1012E200A49D180 5 10 15 20A B A C B C B D D E E DE0 0 1 0 1 1 2 0 1 0 1 2 2 queueFigure 2.11 Exponential FB scheduleThe statistics for our process set are as follows.Process Arrival Service Finish T M Pname time required time A 0 3 4 4 1 1.3 B 1 5 10 9 4 1.8 C 3 2 8 5 3 2.5 D 9 5 18 9 4 1.8 E 12 5 20 8 3 1.6Mean 7.0 3.0 1.8(2) Let a process in queue n be scheduled by RR for 2 n (or perhaps just n ) quantabefore being demoted to the next queue.(3) Promote a process to a higher-priority queue after it spends a certain amount oftime waiting for service in its current queue.(4) Instead of granting absolute priority to low-numbered queues, grant slices of timeto each queue, with lower-numbered queues receiving larger slices.These variants can be used by themselves or in any combination.2.7 Selfish round robin (SRR)The selfish round robin method adds a new dimension to round robin by giving betterservice to processes that have been executing for a while than to newcomers. Processesin the ready list are partitioned into two lists: new and accepted. New processes wait.Accepted processes are serviced by RR. The priority of a new process increases at ratea . The priority of an accepted process increases at rate b . Both a and b are