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SubjectRe: Elevator vs first-come-first-served
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>However, with an intelligent caching disk controller (either on the 
>HBA, or a SCSI-SCSI RAID controller), the sorting of disk blocks can actually
>decrease performance.

Given the general range of opinions on this subject, and especially
the possibility that the "usual" sorting might reduce performance, it seems
to me that the best option is to modularize.

1) The kernel will contain an initial sorting algorithm, which is
likely to be the current one-way elevator.

2) A loadable module (per system? SCSI controller? disk drive?
filesystem? depends upon the hardware) could be used to provide
a more advanced sorting algorithm.


If you want, after the system boots, a user-level program
could measure the read timing on the drives (after the rest of the
system has settled down? during the initial startup itself?
interesting options to explore) and load the sorting module(s) with
configuration-specific parameters.

It would be an interesting student research project, for
example, to make a neural net request sorter...

Craig Milo Rogers


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