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Friday, March 27, 2009

Disk Scheduling In Linux

In a disk, an access time is too big, since it has a mechanical part - disk head which is moving on the disk. It makes overwhole performance of a disk too poor.

Formal problem statement:

Input: A set of requests
Input: The current disk head location
Input: Algorithm state (direction)

Output: the next disk block to get

The goals:

1. Maximize throughput
2. Maximize fairness
3. Avoid starvation
4. Real time concerns

Some scheduling algorithms:

1. A pessimal algorithm
2. An optimal algorithm - shortest service time first
3. First come first serve
4. Elevator
5. Cyclic elevator
6. Deadline scheduler
7. Anticipatory scheduling
8. Completely fair queuing


Andrew Morton said, "the anticipatory shceduler is wiping the others off the map!"

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