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The staircase schedulerThe staircase schedulerPosted Jun 3, 2004 5:08 UTC (Thu) by error27 (subscriber, #8346)In reply to: The staircase scheduler by gallir Parent article: The staircase scheduler To be honest, the definition of "multilevel feedback queues" is too vague to be worthwhile. The old scheduler fits the definition, and the new scheduler doesn't change that at all. What the new scheduler changes is how the processes move from one queue to the other. The stair case scheduler is pretty inovative actually. If you want to learn more about the difficult issues for schedulers read Con's write up here. It's pretty weird to not have an expired array. It seems like a reasonable scheduler design because it obviously gives priority to interactive processes and it doesn't starve any processes. I can see how this would be simpler to code. It's a nice design. I guess the real proof is in testing. :)
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The staircase scheduler Posted Jun 3, 2004 15:30 UTC (Thu) by gallir (guest, #5735) [Link] If you read any OS book, it's comprehensively explained. I suppose youdon't expect to give a full description in a "title" :-). For example, taking an old Peterson/Silberschatz book: "... Multilevel feedback queues, however, allow a process to move between queues. The idea is to separate out processes with a different cpu-burts characteristics. If a process uses too much cpu time, it will be moved to a lower priority queue. This scheme leaves I/O-bound and interactive processes in the higher priority queues. Similarly, a process which waits too long in a lower-priority queue may be moved to a higher priority queue. This is a form of aging that would pevent starvation. ..." Or from a Stalling's book: "... This approach is known as multilevel feedback, meaning that the operating system allocates the processor to a process, and when the process blocks or is preempted, feeds it back into one of several queues. There are a numbre of variations on this scheme. A simple version is to perform preemption inthe same fashions for round-robin: at periodic intervals..." What I mean, a lot of "new methods", for example those applied to CPU and I/O schedulers are already described, discussed, and compared in the literature since the '70 or '80s.
The staircase scheduler Posted Jun 4, 2004 2:40 UTC (Fri) by error27 (subscriber, #8346) [Link] > Multilevel feedback queues, however, allow a process to move betweenqueues. Right. With both the regular scheduler and the stair case scheduler you have 140 queues that represent 140 different priorities. You execute the top priorities first in a round robin format. The trick with the stair case scheduler is the logic behind how the processes move from one queue to the other. > There are a number of variations on this scheme. Exactly. In some ways, you could say that this was "just" a new variation. But in other ways, it's a pretty inovative variation. ;)
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